diff --git a/crates/examples/src/bin/elfcopy.rs b/crates/examples/src/bin/elfcopy.rs
index c2518f81..16a4e4b8 100644
--- a/crates/examples/src/bin/elfcopy.rs
+++ b/crates/examples/src/bin/elfcopy.rs
@@ -1,14 +1,8 @@
-use std::convert::TryInto;
-use std::error::Error;
-use std::{env, fs, process};
-
-use object::elf;
-use object::read::elf::{Dyn, FileHeader, ProgramHeader, Rel, Rela, SectionHeader, Sym};
-use object::Endianness;
-
 use std::collections::HashMap;
+use std::error::Error;
 use std::fs::File;
 use std::io::{self, BufRead};
+use std::{env, fs, process};
 
 fn main() {
     let mut args = env::args();
@@ -53,57 +47,24 @@ fn main() {
     };
     let in_data = &*in_data;
 
-    let kind = match object::FileKind::parse(in_data) {
-        Ok(file) => file,
-        Err(err) => {
-            eprintln!("Failed to parse file: {}", err);
-            process::exit(1);
-        }
-    };
-    let out_data = match kind {
-        object::FileKind::Elf32 => {
-            copy_file::<elf::FileHeader32<Endianness>>(in_data, redefine_file).unwrap()
-        }
-        object::FileKind::Elf64 => {
-            copy_file::<elf::FileHeader64<Endianness>>(in_data, redefine_file).unwrap()
-        }
-        _ => {
-            eprintln!("Not an ELF file");
-            process::exit(1);
-        }
-    };
+    let mut builder = object::write::elf::Builder::read(in_data).unwrap();
+
+    let redefine_table = RedefineSymTable::new(redefine_file).unwrap();
+    for symbol in &mut builder.dynamic_symbols {
+        symbol.name = redefine_table.get_redefined_name(symbol.name);
+    }
+    for symbol in &mut builder.symbols {
+        symbol.name = redefine_table.get_redefined_name(symbol.name);
+    }
+
+    let mut out_data = Vec::new();
+    builder.write(&mut out_data).unwrap();
     if let Err(err) = fs::write(&out_file_path, out_data) {
         eprintln!("Failed to write file '{}': {}", out_file_path, err);
         process::exit(1);
     }
 }
 
-struct Section {
-    name: Option<object::write::StringId>,
-    offset: usize,
-}
-
-struct Dynamic {
-    tag: u32,
-    // Ignored if `string` is set.
-    val: u64,
-    string: Option<object::write::StringId>,
-}
-
-struct Symbol {
-    in_sym: usize,
-    name: Option<object::write::StringId>,
-    section: Option<object::write::elf::SectionIndex>,
-}
-
-struct DynamicSymbol {
-    in_sym: usize,
-    name: Option<object::write::StringId>,
-    section: Option<object::write::elf::SectionIndex>,
-    hash: Option<u32>,
-    gnu_hash: Option<u32>,
-}
-
 /// Table that holds a map of the symbols we should rename while copying
 ///
 /// This will be loaded by passing a file with lines of the form:
@@ -157,847 +118,3 @@ impl RedefineSymTable {
         original
     }
 }
-
-fn copy_file<Elf: FileHeader<Endian = Endianness>>(
-    in_data: &[u8],
-    redefine_file: Option<String>,
-) -> Result<Vec<u8>, Box<dyn Error>> {
-    let in_elf = Elf::parse(in_data)?;
-    let endian = in_elf.endian()?;
-    let is_mips64el = in_elf.is_mips64el(endian);
-    let in_segments = in_elf.program_headers(endian, in_data)?;
-    let in_sections = in_elf.sections(endian, in_data)?;
-    let in_syms = in_sections.symbols(endian, in_data, elf::SHT_SYMTAB)?;
-    let in_dynsyms = in_sections.symbols(endian, in_data, elf::SHT_DYNSYM)?;
-
-    let redefine_table = RedefineSymTable::new(redefine_file)?;
-
-    let mut out_data = Vec::new();
-    let mut writer = object::write::elf::Writer::new(endian, in_elf.is_class_64(), &mut out_data);
-
-    // Find metadata sections, and assign section indices.
-    let mut in_dynamic = None;
-    let mut in_hash = None;
-    let mut in_gnu_hash = None;
-    let mut in_versym = None;
-    let mut in_verdef = None;
-    let mut in_verneed = None;
-    let mut in_attributes = None;
-    let mut out_sections = Vec::with_capacity(in_sections.len());
-    let mut out_sections_index = Vec::with_capacity(in_sections.len());
-    for (i, in_section) in in_sections.iter().enumerate() {
-        let mut name = None;
-        let index;
-        match in_section.sh_type(endian) {
-            elf::SHT_NULL => {
-                index = writer.reserve_null_section_index();
-            }
-            elf::SHT_PROGBITS
-            | elf::SHT_NOBITS
-            | elf::SHT_NOTE
-            | elf::SHT_REL
-            | elf::SHT_RELA
-            | elf::SHT_INIT_ARRAY
-            | elf::SHT_FINI_ARRAY => {
-                name = Some(writer.add_section_name(in_sections.section_name(endian, in_section)?));
-                index = writer.reserve_section_index();
-            }
-            elf::SHT_STRTAB => {
-                if i == in_syms.string_section().0 {
-                    index = writer.reserve_strtab_section_index();
-                } else if i == in_dynsyms.string_section().0 {
-                    index = writer.reserve_dynstr_section_index();
-                } else if i == in_elf.shstrndx(endian, in_data)? as usize {
-                    index = writer.reserve_shstrtab_section_index();
-                } else {
-                    panic!("Unsupported string section {}", i);
-                }
-            }
-            elf::SHT_SYMTAB => {
-                if i == in_syms.section().0 {
-                    index = writer.reserve_symtab_section_index();
-                } else {
-                    panic!("Unsupported symtab section {}", i);
-                }
-            }
-            elf::SHT_SYMTAB_SHNDX => {
-                if i == in_syms.shndx_section().0 {
-                    index = writer.reserve_symtab_shndx_section_index();
-                } else {
-                    panic!("Unsupported symtab shndx section {}", i);
-                }
-            }
-            elf::SHT_DYNSYM => {
-                if i == in_dynsyms.section().0 {
-                    index = writer.reserve_dynsym_section_index();
-                } else {
-                    panic!("Unsupported dynsym section {}", i);
-                }
-            }
-            elf::SHT_DYNAMIC => {
-                assert!(in_dynamic.is_none());
-                in_dynamic = in_section.dynamic(endian, in_data)?;
-                debug_assert!(in_dynamic.is_some());
-                index = writer.reserve_dynamic_section_index();
-            }
-            elf::SHT_HASH => {
-                assert!(in_hash.is_none());
-                in_hash = in_section.hash_header(endian, in_data)?;
-                debug_assert!(in_hash.is_some());
-                index = writer.reserve_hash_section_index();
-            }
-            elf::SHT_GNU_HASH => {
-                assert!(in_gnu_hash.is_none());
-                in_gnu_hash = in_section.gnu_hash_header(endian, in_data)?;
-                debug_assert!(in_gnu_hash.is_some());
-                index = writer.reserve_gnu_hash_section_index();
-            }
-            elf::SHT_GNU_VERSYM => {
-                in_versym = in_section.gnu_versym(endian, in_data)?;
-                debug_assert!(in_versym.is_some());
-                index = writer.reserve_gnu_versym_section_index();
-            }
-            elf::SHT_GNU_VERDEF => {
-                in_verdef = in_section.gnu_verdef(endian, in_data)?;
-                debug_assert!(in_verdef.is_some());
-                index = writer.reserve_gnu_verdef_section_index();
-            }
-            elf::SHT_GNU_VERNEED => {
-                in_verneed = in_section.gnu_verneed(endian, in_data)?;
-                debug_assert!(in_verneed.is_some());
-                index = writer.reserve_gnu_verneed_section_index();
-            }
-            elf::SHT_GNU_ATTRIBUTES => {
-                in_attributes = in_section.gnu_attributes(endian, in_data)?;
-                debug_assert!(in_attributes.is_some());
-                index = writer.reserve_gnu_attributes_section_index();
-            }
-            other => {
-                panic!("Unsupported section type {:x}", other);
-            }
-        }
-        out_sections.push(Section { name, offset: 0 });
-        out_sections_index.push(index);
-    }
-
-    // Assign dynamic strings.
-    let mut out_dynamic = Vec::new();
-    if let Some((in_dynamic, link)) = in_dynamic {
-        out_dynamic.reserve(in_dynamic.len());
-        let in_dynamic_strings = in_sections.strings(endian, in_data, link)?;
-        for d in in_dynamic {
-            let tag = d.d_tag(endian).into().try_into()?;
-            let val = d.d_val(endian).into();
-            let string = if d.is_string(endian) {
-                let s = in_dynamic_strings
-                    .get(val.try_into()?)
-                    .map_err(|_| "Invalid dynamic string")?;
-                Some(writer.add_dynamic_string(s))
-            } else {
-                None
-            };
-            out_dynamic.push(Dynamic { tag, val, string });
-            if tag == elf::DT_NULL {
-                break;
-            }
-        }
-    }
-
-    // Assign dynamic symbol indices.
-    let mut out_dynsyms = Vec::with_capacity(in_dynsyms.len());
-    for (i, in_dynsym) in in_dynsyms.iter().enumerate().skip(1) {
-        let section = match in_dynsyms.symbol_section(endian, in_dynsym, i)? {
-            Some(in_section) => {
-                // Skip symbols for sections we aren't copying.
-                if out_sections_index[in_section.0].0 == 0 {
-                    continue;
-                }
-                Some(out_sections_index[in_section.0])
-            }
-            None => None,
-        };
-        let mut name = None;
-        let mut hash = None;
-        let mut gnu_hash = None;
-        if in_dynsym.st_name(endian) != 0 {
-            let in_name = in_dynsyms.symbol_name(endian, in_dynsym)?;
-            let redefined_name = redefine_table.get_redefined_name(in_name);
-            name = Some(writer.add_dynamic_string(redefined_name));
-            if !redefined_name.is_empty() {
-                hash = Some(elf::hash(redefined_name));
-                if !in_dynsym.is_undefined(endian) {
-                    gnu_hash = Some(elf::gnu_hash(redefined_name));
-                }
-            }
-        };
-        out_dynsyms.push(DynamicSymbol {
-            in_sym: i,
-            name,
-            section,
-            hash,
-            gnu_hash,
-        });
-    }
-    // We must sort for GNU hash before allocating symbol indices.
-    if let Some(in_gnu_hash) = in_gnu_hash.as_ref() {
-        // TODO: recalculate bucket_count
-        out_dynsyms.sort_by_key(|sym| match sym.gnu_hash {
-            None => (0, 0),
-            Some(hash) => (1, hash % in_gnu_hash.bucket_count.get(endian)),
-        });
-    }
-    let mut out_dynsyms_index = vec![Default::default(); in_dynsyms.len()];
-    for out_dynsym in out_dynsyms.iter_mut() {
-        out_dynsyms_index[out_dynsym.in_sym] = writer.reserve_dynamic_symbol_index();
-    }
-
-    // Hash parameters.
-    let hash_index_base = out_dynsyms
-        .first()
-        .map(|sym| out_dynsyms_index[sym.in_sym].0)
-        .unwrap_or(0);
-    let hash_chain_count = writer.dynamic_symbol_count();
-
-    // GNU hash parameters.
-    let gnu_hash_index_base = out_dynsyms
-        .iter()
-        .position(|sym| sym.gnu_hash.is_some())
-        .unwrap_or(0);
-    let gnu_hash_symbol_base = out_dynsyms
-        .iter()
-        .find(|sym| sym.gnu_hash.is_some())
-        .map(|sym| out_dynsyms_index[sym.in_sym].0)
-        .unwrap_or_else(|| writer.dynamic_symbol_count());
-    let gnu_hash_symbol_count = writer.dynamic_symbol_count() - gnu_hash_symbol_base;
-
-    // Assign symbol indices.
-    let mut num_local = 0;
-    let mut out_syms = Vec::with_capacity(in_syms.len());
-    let mut out_syms_index = Vec::with_capacity(in_syms.len());
-    out_syms_index.push(Default::default());
-    for (i, in_sym) in in_syms.iter().enumerate().skip(1) {
-        let section = match in_syms.symbol_section(endian, in_sym, i)? {
-            Some(in_section) => {
-                // Skip symbols for sections we aren't copying.
-                if out_sections_index[in_section.0].0 == 0 {
-                    out_syms_index.push(Default::default());
-                    continue;
-                }
-                Some(out_sections_index[in_section.0])
-            }
-            None => None,
-        };
-        out_syms_index.push(writer.reserve_symbol_index(section));
-        let name = if in_sym.st_name(endian) != 0 {
-            Some(writer.add_string(
-                redefine_table.get_redefined_name(in_syms.symbol_name(endian, in_sym)?),
-            ))
-        } else {
-            None
-        };
-        out_syms.push(Symbol {
-            in_sym: i,
-            name,
-            section,
-        });
-        if in_sym.st_bind() == elf::STB_LOCAL {
-            num_local = writer.symbol_count();
-        }
-    }
-
-    // Symbol version parameters.
-    let mut verdef_count = 0;
-    let mut verdaux_count = 0;
-    if let Some((mut verdefs, link)) = in_verdef.clone() {
-        let strings = in_sections.strings(endian, in_data, link)?;
-        while let Some((verdef, mut verdauxs)) = verdefs.next()? {
-            assert!(verdef.vd_cnt.get(endian) > 0);
-            verdef_count += 1;
-            while let Some(verdaux) = verdauxs.next()? {
-                writer.add_dynamic_string(verdaux.name(endian, strings)?);
-                verdaux_count += 1;
-            }
-        }
-    }
-
-    let mut verneed_count = 0;
-    let mut vernaux_count = 0;
-    if let Some((mut verneeds, link)) = in_verneed.clone() {
-        let strings = in_sections.strings(endian, in_data, link)?;
-        while let Some((verneed, mut vernauxs)) = verneeds.next()? {
-            writer.add_dynamic_string(verneed.file(endian, strings)?);
-            verneed_count += 1;
-            while let Some(vernaux) = vernauxs.next()? {
-                writer.add_dynamic_string(vernaux.name(endian, strings)?);
-                vernaux_count += 1;
-            }
-        }
-    }
-
-    let mut gnu_attributes = Vec::new();
-    if let Some(attributes) = in_attributes {
-        let mut writer = writer.attributes_writer();
-        let mut subsections = attributes.subsections()?;
-        while let Some(subsection) = subsections.next()? {
-            writer.start_subsection(subsection.vendor());
-            let mut subsubsections = subsection.subsubsections();
-            while let Some(subsubsection) = subsubsections.next()? {
-                writer.start_subsubsection(subsubsection.tag());
-                match subsubsection.tag() {
-                    elf::Tag_File => {}
-                    elf::Tag_Section => {
-                        let mut indices = subsubsection.indices();
-                        while let Some(index) = indices.next()? {
-                            writer.write_subsubsection_index(out_sections_index[index as usize].0);
-                        }
-                        writer.write_subsubsection_index(0);
-                    }
-                    elf::Tag_Symbol => {
-                        let mut indices = subsubsection.indices();
-                        while let Some(index) = indices.next()? {
-                            writer.write_subsubsection_index(out_syms_index[index as usize].0);
-                        }
-                        writer.write_subsubsection_index(0);
-                    }
-                    _ => unimplemented!(),
-                }
-                writer.write_subsubsection_attributes(subsubsection.attributes_data());
-                writer.end_subsubsection();
-            }
-            writer.end_subsection();
-        }
-        gnu_attributes = writer.data();
-        assert_ne!(gnu_attributes.len(), 0);
-    }
-
-    // Start reserving file ranges.
-    writer.reserve_file_header();
-
-    let mut hash_addr = 0;
-    let mut gnu_hash_addr = 0;
-    let mut versym_addr = 0;
-    let mut verdef_addr = 0;
-    let mut verneed_addr = 0;
-    let mut dynamic_addr = 0;
-    let mut dynsym_addr = 0;
-    let mut dynstr_addr = 0;
-
-    let mut alloc_sections = Vec::new();
-    if in_segments.is_empty() {
-        // Reserve sections at any offset.
-        for (i, in_section) in in_sections.iter().enumerate() {
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE | elf::SHT_INIT_ARRAY | elf::SHT_FINI_ARRAY => {
-                    out_sections[i].offset = writer.reserve(
-                        in_section.sh_size(endian).into() as usize,
-                        in_section.sh_addralign(endian).into() as usize,
-                    );
-                }
-                elf::SHT_GNU_ATTRIBUTES => {
-                    writer.reserve_gnu_attributes(gnu_attributes.len());
-                }
-                _ => {}
-            }
-        }
-    } else {
-        // We don't support moving program headers.
-        assert_eq!(in_elf.e_phoff(endian).into(), writer.reserved_len() as u64);
-        writer.reserve_program_headers(in_segments.len() as u32);
-
-        // Reserve alloc sections at original offsets.
-        alloc_sections = in_sections
-            .iter()
-            .enumerate()
-            .filter(|(_, s)| s.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0)
-            .collect();
-        // The data for alloc sections may need to be written in a different order
-        // from their section headers.
-        alloc_sections.sort_by_key(|(_, x)| x.sh_offset(endian).into());
-        for (i, in_section) in alloc_sections.iter() {
-            writer.reserve_until(in_section.sh_offset(endian).into() as usize);
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE | elf::SHT_INIT_ARRAY | elf::SHT_FINI_ARRAY => {
-                    out_sections[*i].offset =
-                        writer.reserve(in_section.sh_size(endian).into() as usize, 1);
-                }
-                elf::SHT_NOBITS => {
-                    out_sections[*i].offset = writer.reserved_len();
-                }
-                elf::SHT_REL => {
-                    let (rels, _link) = in_section.rel(endian, in_data)?.unwrap();
-                    out_sections[*i].offset = writer.reserve_relocations(rels.len(), false);
-                }
-                elf::SHT_RELA => {
-                    let (rels, _link) = in_section.rela(endian, in_data)?.unwrap();
-                    out_sections[*i].offset = writer.reserve_relocations(rels.len(), true);
-                }
-                elf::SHT_DYNAMIC => {
-                    dynamic_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_dynamic(out_dynamic.len());
-                }
-                elf::SHT_DYNSYM if *i == in_dynsyms.section().0 => {
-                    dynsym_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_dynsym();
-                }
-                elf::SHT_STRTAB if *i == in_dynsyms.string_section().0 => {
-                    dynstr_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_dynstr();
-                }
-                elf::SHT_HASH => {
-                    hash_addr = in_section.sh_addr(endian).into();
-                    let hash = in_hash.as_ref().unwrap();
-                    writer.reserve_hash(hash.bucket_count.get(endian), hash_chain_count);
-                }
-                elf::SHT_GNU_HASH => {
-                    gnu_hash_addr = in_section.sh_addr(endian).into();
-                    let hash = in_gnu_hash.as_ref().unwrap();
-                    writer.reserve_gnu_hash(
-                        hash.bloom_count.get(endian),
-                        hash.bucket_count.get(endian),
-                        gnu_hash_symbol_count,
-                    );
-                }
-                elf::SHT_GNU_VERSYM => {
-                    versym_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_gnu_versym();
-                }
-                elf::SHT_GNU_VERDEF => {
-                    verdef_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_gnu_verdef(verdef_count, verdaux_count);
-                }
-                elf::SHT_GNU_VERNEED => {
-                    verneed_addr = in_section.sh_addr(endian).into();
-                    writer.reserve_gnu_verneed(verneed_count, vernaux_count);
-                }
-                other => {
-                    panic!("Unsupported alloc section index {}, type {}", *i, other);
-                }
-            }
-        }
-
-        // Reserve non-alloc sections at any offset.
-        for (i, in_section) in in_sections.iter().enumerate() {
-            if in_section.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0 {
-                continue;
-            }
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE => {
-                    out_sections[i].offset = writer.reserve(
-                        in_section.sh_size(endian).into() as usize,
-                        in_section.sh_addralign(endian).into() as usize,
-                    );
-                }
-                elf::SHT_GNU_ATTRIBUTES => {
-                    writer.reserve_gnu_attributes(gnu_attributes.len());
-                }
-                _ => {}
-            }
-        }
-    }
-
-    writer.reserve_symtab();
-    writer.reserve_symtab_shndx();
-    writer.reserve_strtab();
-
-    for (i, in_section) in in_sections.iter().enumerate() {
-        if !in_segments.is_empty()
-            && in_section.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0
-        {
-            continue;
-        }
-        match in_section.sh_type(endian) {
-            elf::SHT_REL => {
-                let (rels, _link) = in_section.rel(endian, in_data)?.unwrap();
-                out_sections[i].offset = writer.reserve_relocations(rels.len(), false);
-            }
-            elf::SHT_RELA => {
-                let (rels, _link) = in_section.rela(endian, in_data)?.unwrap();
-                out_sections[i].offset = writer.reserve_relocations(rels.len(), true);
-            }
-            _ => {}
-        }
-    }
-
-    writer.reserve_shstrtab();
-    writer.reserve_section_headers();
-
-    writer.write_file_header(&object::write::elf::FileHeader {
-        os_abi: in_elf.e_ident().os_abi,
-        abi_version: in_elf.e_ident().abi_version,
-        e_type: in_elf.e_type(endian),
-        e_machine: in_elf.e_machine(endian),
-        e_entry: in_elf.e_entry(endian).into(),
-        e_flags: in_elf.e_flags(endian),
-    })?;
-
-    if in_segments.is_empty() {
-        for (i, in_section) in in_sections.iter().enumerate() {
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE | elf::SHT_INIT_ARRAY | elf::SHT_FINI_ARRAY => {
-                    writer.write_align(in_section.sh_addralign(endian).into() as usize);
-                    debug_assert_eq!(out_sections[i].offset, writer.len());
-                    writer.write(in_section.data(endian, in_data)?);
-                }
-                elf::SHT_GNU_ATTRIBUTES => {
-                    writer.write_gnu_attributes(&gnu_attributes);
-                }
-                _ => {}
-            }
-        }
-    } else {
-        writer.write_align_program_headers();
-        for in_segment in in_segments {
-            writer.write_program_header(&object::write::elf::ProgramHeader {
-                p_type: in_segment.p_type(endian),
-                p_flags: in_segment.p_flags(endian),
-                p_offset: in_segment.p_offset(endian).into(),
-                p_vaddr: in_segment.p_vaddr(endian).into(),
-                p_paddr: in_segment.p_paddr(endian).into(),
-                p_filesz: in_segment.p_filesz(endian).into(),
-                p_memsz: in_segment.p_memsz(endian).into(),
-                p_align: in_segment.p_align(endian).into(),
-            });
-        }
-
-        for (i, in_section) in alloc_sections.iter() {
-            writer.pad_until(in_section.sh_offset(endian).into() as usize);
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE | elf::SHT_INIT_ARRAY | elf::SHT_FINI_ARRAY => {
-                    debug_assert_eq!(out_sections[*i].offset, writer.len());
-                    writer.write(in_section.data(endian, in_data)?);
-                }
-                elf::SHT_NOBITS => {}
-                elf::SHT_REL => {
-                    let (rels, _link) = in_section.rel(endian, in_data)?.unwrap();
-                    writer.write_align_relocation();
-                    for rel in rels {
-                        let in_sym = rel.r_sym(endian);
-                        let out_sym = if in_sym != 0 {
-                            out_dynsyms_index[in_sym as usize].0
-                        } else {
-                            0
-                        };
-                        writer.write_relocation(
-                            false,
-                            &object::write::elf::Rel {
-                                r_offset: rel.r_offset(endian).into(),
-                                r_sym: out_sym,
-                                r_type: rel.r_type(endian),
-                                r_addend: 0,
-                            },
-                        );
-                    }
-                }
-                elf::SHT_RELA => {
-                    let (rels, _link) = in_section.rela(endian, in_data)?.unwrap();
-                    writer.write_align_relocation();
-                    for rel in rels {
-                        let in_sym = rel.r_sym(endian, is_mips64el);
-                        let out_sym = if in_sym != 0 {
-                            out_dynsyms_index[in_sym as usize].0
-                        } else {
-                            0
-                        };
-                        writer.write_relocation(
-                            true,
-                            &object::write::elf::Rel {
-                                r_offset: rel.r_offset(endian).into(),
-                                r_sym: out_sym,
-                                r_type: rel.r_type(endian, is_mips64el),
-                                r_addend: rel.r_addend(endian).into(),
-                            },
-                        );
-                    }
-                }
-                elf::SHT_DYNAMIC => {
-                    for d in &out_dynamic {
-                        if let Some(string) = d.string {
-                            writer.write_dynamic_string(d.tag, string);
-                        } else {
-                            // TODO: fix values
-                            let val = d.val;
-                            writer.write_dynamic(d.tag, val);
-                        }
-                    }
-                }
-                elf::SHT_DYNSYM if *i == in_dynsyms.section().0 => {
-                    writer.write_null_dynamic_symbol();
-                    for sym in &out_dynsyms {
-                        let in_dynsym = in_dynsyms.symbol(sym.in_sym)?;
-                        writer.write_dynamic_symbol(&object::write::elf::Sym {
-                            name: sym.name,
-                            section: sym.section,
-                            st_info: in_dynsym.st_info(),
-                            st_other: in_dynsym.st_other(),
-                            st_shndx: in_dynsym.st_shndx(endian),
-                            st_value: in_dynsym.st_value(endian).into(),
-                            st_size: in_dynsym.st_size(endian).into(),
-                        });
-                    }
-                }
-                elf::SHT_STRTAB if *i == in_dynsyms.string_section().0 => {
-                    writer.write_dynstr();
-                }
-                elf::SHT_HASH => {
-                    let hash = in_hash.as_ref().unwrap();
-                    writer.write_hash(hash.bucket_count.get(endian), hash_chain_count, |index| {
-                        out_dynsyms
-                            .get(index.checked_sub(hash_index_base)? as usize)?
-                            .hash
-                    });
-                }
-                elf::SHT_GNU_HASH => {
-                    let gnu_hash = in_gnu_hash.as_ref().unwrap();
-                    writer.write_gnu_hash(
-                        gnu_hash_symbol_base,
-                        gnu_hash.bloom_shift.get(endian),
-                        gnu_hash.bloom_count.get(endian),
-                        gnu_hash.bucket_count.get(endian),
-                        gnu_hash_symbol_count,
-                        |index| {
-                            out_dynsyms[gnu_hash_index_base + index as usize]
-                                .gnu_hash
-                                .unwrap()
-                        },
-                    );
-                }
-                elf::SHT_GNU_VERSYM => {
-                    let (in_versym, _) = in_versym.as_ref().unwrap();
-                    writer.write_null_gnu_versym();
-                    for out_dynsym in &out_dynsyms {
-                        writer.write_gnu_versym(
-                            in_versym.get(out_dynsym.in_sym).unwrap().0.get(endian),
-                        );
-                    }
-                }
-                elf::SHT_GNU_VERDEF => {
-                    let (mut verdefs, link) = in_verdef.clone().unwrap();
-                    let strings = in_sections.strings(endian, in_data, link)?;
-                    writer.write_align_gnu_verdef();
-                    while let Some((verdef, mut verdauxs)) = verdefs.next()? {
-                        let verdaux = verdauxs.next()?.unwrap();
-                        writer.write_gnu_verdef(&object::write::elf::Verdef {
-                            version: verdef.vd_version.get(endian),
-                            flags: verdef.vd_flags.get(endian),
-                            index: verdef.vd_ndx.get(endian),
-                            aux_count: verdef.vd_cnt.get(endian),
-                            name: writer.get_dynamic_string(verdaux.name(endian, strings)?),
-                        });
-                        while let Some(verdaux) = verdauxs.next()? {
-                            writer.write_gnu_verdaux(
-                                writer.get_dynamic_string(verdaux.name(endian, strings)?),
-                            );
-                        }
-                    }
-                }
-                elf::SHT_GNU_VERNEED => {
-                    let (mut verneeds, link) = in_verneed.clone().unwrap();
-                    let strings = in_sections.strings(endian, in_data, link)?;
-                    writer.write_align_gnu_verneed();
-                    while let Some((verneed, mut vernauxs)) = verneeds.next()? {
-                        writer.write_gnu_verneed(&object::write::elf::Verneed {
-                            version: verneed.vn_version.get(endian),
-                            aux_count: verneed.vn_cnt.get(endian),
-                            file: writer.get_dynamic_string(verneed.file(endian, strings)?),
-                        });
-                        while let Some(vernaux) = vernauxs.next()? {
-                            writer.write_gnu_vernaux(&object::write::elf::Vernaux {
-                                flags: vernaux.vna_flags.get(endian),
-                                index: vernaux.vna_other.get(endian),
-                                name: writer.get_dynamic_string(vernaux.name(endian, strings)?),
-                            });
-                        }
-                    }
-                }
-                other => {
-                    panic!("Unsupported alloc section type {:x}", other);
-                }
-            }
-        }
-
-        for (i, in_section) in in_sections.iter().enumerate() {
-            if in_section.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0 {
-                continue;
-            }
-            match in_section.sh_type(endian) {
-                elf::SHT_PROGBITS | elf::SHT_NOTE => {
-                    writer.write_align(in_section.sh_addralign(endian).into() as usize);
-                    debug_assert_eq!(out_sections[i].offset, writer.len());
-                    writer.write(in_section.data(endian, in_data)?);
-                }
-                elf::SHT_GNU_ATTRIBUTES => {
-                    writer.write_gnu_attributes(&gnu_attributes);
-                }
-                _ => {}
-            }
-        }
-    }
-
-    writer.write_null_symbol();
-    for sym in &out_syms {
-        let in_sym = in_syms.symbol(sym.in_sym)?;
-        writer.write_symbol(&object::write::elf::Sym {
-            name: sym.name,
-            section: sym.section,
-            st_info: in_sym.st_info(),
-            st_other: in_sym.st_other(),
-            st_shndx: in_sym.st_shndx(endian),
-            st_value: in_sym.st_value(endian).into(),
-            st_size: in_sym.st_size(endian).into(),
-        });
-    }
-    writer.write_symtab_shndx();
-    writer.write_strtab();
-
-    for in_section in in_sections.iter() {
-        if !in_segments.is_empty()
-            && in_section.sh_flags(endian).into() & u64::from(elf::SHF_ALLOC) != 0
-        {
-            continue;
-        }
-        let out_syms = if in_section.sh_link(endian) as usize == in_syms.section().0 {
-            &out_syms_index
-        } else {
-            &out_dynsyms_index
-        };
-        match in_section.sh_type(endian) {
-            elf::SHT_REL => {
-                let (rels, _link) = in_section.rel(endian, in_data)?.unwrap();
-                writer.write_align_relocation();
-                for rel in rels {
-                    let in_sym = rel.r_sym(endian);
-                    let out_sym = if in_sym != 0 {
-                        out_syms[in_sym as usize].0
-                    } else {
-                        0
-                    };
-                    writer.write_relocation(
-                        false,
-                        &object::write::elf::Rel {
-                            r_offset: rel.r_offset(endian).into(),
-                            r_sym: out_sym,
-                            r_type: rel.r_type(endian),
-                            r_addend: 0,
-                        },
-                    );
-                }
-            }
-            elf::SHT_RELA => {
-                let (rels, _link) = in_section.rela(endian, in_data)?.unwrap();
-                writer.write_align_relocation();
-                for rel in rels {
-                    let in_sym = rel.r_sym(endian, is_mips64el);
-                    let out_sym = if in_sym != 0 {
-                        out_syms[in_sym as usize].0
-                    } else {
-                        0
-                    };
-                    writer.write_relocation(
-                        true,
-                        &object::write::elf::Rel {
-                            r_offset: rel.r_offset(endian).into(),
-                            r_sym: out_sym,
-                            r_type: rel.r_type(endian, is_mips64el),
-                            r_addend: rel.r_addend(endian).into(),
-                        },
-                    );
-                }
-            }
-            _ => {}
-        }
-    }
-
-    writer.write_shstrtab();
-
-    writer.write_null_section_header();
-    for (i, in_section) in in_sections.iter().enumerate() {
-        match in_section.sh_type(endian) {
-            elf::SHT_NULL => {}
-            elf::SHT_PROGBITS
-            | elf::SHT_NOBITS
-            | elf::SHT_NOTE
-            | elf::SHT_REL
-            | elf::SHT_RELA
-            | elf::SHT_INIT_ARRAY
-            | elf::SHT_FINI_ARRAY => {
-                let out_section = &out_sections[i];
-                let sh_link = out_sections_index[in_section.sh_link(endian) as usize].0;
-                let mut sh_info = in_section.sh_info(endian);
-                if in_section.sh_flags(endian).into() as u32 & elf::SHF_INFO_LINK != 0 {
-                    sh_info = out_sections_index[sh_info as usize].0;
-                }
-                writer.write_section_header(&object::write::elf::SectionHeader {
-                    name: out_section.name,
-                    sh_type: in_section.sh_type(endian),
-                    sh_flags: in_section.sh_flags(endian).into(),
-                    sh_addr: in_section.sh_addr(endian).into(),
-                    sh_offset: out_section.offset as u64,
-                    sh_size: in_section.sh_size(endian).into(),
-                    sh_link,
-                    sh_info,
-                    sh_addralign: in_section.sh_addralign(endian).into(),
-                    sh_entsize: in_section.sh_entsize(endian).into(),
-                });
-            }
-            elf::SHT_STRTAB => {
-                if i == in_syms.string_section().0 {
-                    writer.write_strtab_section_header();
-                } else if i == in_dynsyms.string_section().0 {
-                    writer.write_dynstr_section_header(dynstr_addr);
-                } else if i == in_elf.shstrndx(endian, in_data)? as usize {
-                    writer.write_shstrtab_section_header();
-                } else {
-                    panic!("Unsupported string section {}", i);
-                }
-            }
-            elf::SHT_SYMTAB => {
-                if i == in_syms.section().0 {
-                    writer.write_symtab_section_header(num_local);
-                } else {
-                    panic!("Unsupported symtab section {}", i);
-                }
-            }
-            elf::SHT_SYMTAB_SHNDX => {
-                if i == in_syms.shndx_section().0 {
-                    writer.write_symtab_shndx_section_header();
-                } else {
-                    panic!("Unsupported symtab shndx section {}", i);
-                }
-            }
-            elf::SHT_DYNSYM => {
-                if i == in_dynsyms.section().0 {
-                    writer.write_dynsym_section_header(dynsym_addr, 1);
-                } else {
-                    panic!("Unsupported dynsym section {}", i);
-                }
-            }
-            elf::SHT_DYNAMIC => {
-                writer.write_dynamic_section_header(dynamic_addr);
-            }
-            elf::SHT_HASH => {
-                writer.write_hash_section_header(hash_addr);
-            }
-            elf::SHT_GNU_HASH => {
-                writer.write_gnu_hash_section_header(gnu_hash_addr);
-            }
-            elf::SHT_GNU_VERSYM => {
-                writer.write_gnu_versym_section_header(versym_addr);
-            }
-            elf::SHT_GNU_VERDEF => {
-                writer.write_gnu_verdef_section_header(verdef_addr);
-            }
-            elf::SHT_GNU_VERNEED => {
-                writer.write_gnu_verneed_section_header(verneed_addr);
-            }
-            elf::SHT_GNU_ATTRIBUTES => {
-                writer.write_gnu_attributes_section_header();
-            }
-            other => {
-                panic!("Unsupported section type {:x}", other);
-            }
-        }
-    }
-    debug_assert_eq!(writer.reserved_len(), writer.len());
-
-    Ok(out_data)
-}
diff --git a/src/read/mod.rs b/src/read/mod.rs
index c13e3091..364ec3ec 100644
--- a/src/read/mod.rs
+++ b/src/read/mod.rs
@@ -107,7 +107,7 @@ mod private {
 
 /// The error type used within the read module.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub struct Error(&'static str);
+pub struct Error(pub(crate) &'static str);
 
 impl fmt::Display for Error {
     #[inline]
diff --git a/src/write/elf/builder.rs b/src/write/elf/builder.rs
new file mode 100644
index 00000000..5e76e94f
--- /dev/null
+++ b/src/write/elf/builder.rs
@@ -0,0 +1,1703 @@
+#![allow(missing_docs)]
+
+use crate::elf;
+use crate::write::{self, Error, Result, WritableBuffer};
+use crate::Endianness;
+use alloc::vec::Vec;
+use core::marker::PhantomData;
+
+#[cfg(all(feature = "read_core", feature = "elf"))]
+use crate::read::elf::{Dyn, FileHeader, ProgramHeader, Rel, Rela, SectionHeader, Sym};
+#[cfg(all(feature = "read_core", feature = "elf"))]
+use crate::read::{self, FileKind, ReadRef};
+#[cfg(all(feature = "read_core", feature = "elf"))]
+use core::convert::TryInto;
+
+#[cfg(all(feature = "read_core", feature = "elf"))]
+impl From<read::Error> for Error {
+    fn from(error: read::Error) -> Error {
+        Error(format!("{}", error))
+    }
+}
+
+#[derive(Debug)]
+pub struct Builder<'data> {
+    pub endian: Endianness,
+    pub is_64: bool,
+    pub os_abi: u8,
+    pub abi_version: u8,
+    pub e_type: u16,
+    pub e_machine: u16,
+    pub e_entry: u64,
+    pub e_flags: u32,
+    pub e_phoff: usize,
+
+    pub section_names: Option<SectionId>,
+    // TODO: use Cow for data references
+    pub segments: Segments<'data>,
+    pub sections: Sections<'data>,
+    pub symbols: Symbols<'data>,
+    pub dynamic_symbols: Symbols<'data>,
+    pub dynamics: Vec<Dynamic<'data>>,
+    pub version_base: Option<&'data [u8]>,
+    pub versions: Versions<'data>,
+    pub version_files: VersionFiles<'data>,
+    pub hash_bucket_count: u32,
+    pub gnu_hash_bloom_shift: u32,
+    pub gnu_hash_bloom_count: u32,
+    pub gnu_hash_bucket_count: u32,
+    pub gnu_attributes: AttributesSection<'data>,
+}
+
+impl<'data> Builder<'data> {
+    #[cfg(all(feature = "read_core", feature = "elf"))]
+    pub fn read<R: ReadRef<'data>>(data: R) -> Result<Self> {
+        let kind = FileKind::parse(data)?;
+        match kind {
+            FileKind::Elf32 => Self::read_file::<elf::FileHeader32<Endianness>, R>(data),
+            FileKind::Elf64 => Self::read_file::<elf::FileHeader64<Endianness>, R>(data),
+            _ => Err(Error(format!("Not an ELF file"))),
+        }
+    }
+
+    #[cfg(all(feature = "read_core", feature = "elf"))]
+    fn read_file<Elf, R>(data: R) -> Result<Self>
+    where
+        Elf: FileHeader<Endian = Endianness>,
+        R: ReadRef<'data>,
+    {
+        let header = Elf::parse(data)?;
+        let endian = header.endian()?;
+        let is_mips64el = header.is_mips64el(endian);
+        let shstrndx = header.shstrndx(endian, data)? as usize;
+        let segments = header.program_headers(endian, data)?;
+        let sections = header.sections(endian, data)?;
+        let symbols = sections.symbols(endian, data, elf::SHT_SYMTAB)?;
+        let dynamic_symbols = sections.symbols(endian, data, elf::SHT_DYNSYM)?;
+        let gnu_versym = sections.gnu_versym(endian, data)?;
+        let gnu_verdef = sections.gnu_verdef(endian, data)?;
+        let gnu_verneed = sections.gnu_verneed(endian, data)?;
+
+        let mut builder = Builder {
+            endian,
+            is_64: header.is_type_64(),
+            os_abi: header.e_ident().os_abi,
+            abi_version: header.e_ident().abi_version,
+            e_type: header.e_type(endian),
+            e_machine: header.e_machine(endian),
+            e_entry: header.e_entry(endian).into(),
+            e_flags: header.e_flags(endian),
+            e_phoff: header.e_phoff(endian).into() as usize,
+
+            section_names: None,
+            segments: Segments::new(),
+            sections: Sections::new(),
+            symbols: Symbols::new(),
+            dynamic_symbols: Symbols::new(),
+            dynamics: Vec::new(),
+            version_base: None,
+            versions: Versions::new(),
+            version_files: VersionFiles::new(),
+            hash_bucket_count: 0,
+            gnu_hash_bloom_shift: 0,
+            gnu_hash_bloom_count: 0,
+            gnu_hash_bucket_count: 0,
+            gnu_attributes: AttributesSection::new(),
+        };
+
+        for segment in segments {
+            let id = SegmentId(builder.segments.0.len());
+            builder.segments.0.push(Segment {
+                id,
+                p_type: segment.p_type(endian),
+                p_flags: segment.p_flags(endian),
+                p_offset: segment.p_offset(endian).into(),
+                p_vaddr: segment.p_vaddr(endian).into(),
+                p_paddr: segment.p_paddr(endian).into(),
+                p_filesz: segment.p_filesz(endian).into(),
+                p_memsz: segment.p_memsz(endian).into(),
+                p_align: segment.p_align(endian).into(),
+                delete: false,
+                marker: PhantomData,
+            });
+        }
+
+        for (index, section) in sections.iter().enumerate().skip(1) {
+            let id = SectionId(builder.sections.0.len());
+            let relocations = if let Some((rels, _link)) = section.rel(endian, data)? {
+                rels.iter()
+                    .map(|rel| {
+                        let r_sym = rel.r_sym(endian);
+                        let symbol = if r_sym == 0 {
+                            None
+                        } else {
+                            Some(SymbolId(r_sym as usize - 1))
+                        };
+                        Relocation {
+                            r_offset: rel.r_offset(endian).into(),
+                            symbol,
+                            r_type: rel.r_type(endian),
+                            r_addend: 0,
+                            delete: false,
+                        }
+                    })
+                    .collect()
+            } else if let Some((rels, _link)) = section.rela(endian, data)? {
+                rels.iter()
+                    .map(|rel| {
+                        let r_sym = rel.r_sym(endian, is_mips64el);
+                        let symbol = if r_sym == 0 {
+                            None
+                        } else {
+                            Some(SymbolId(r_sym as usize - 1))
+                        };
+                        Relocation {
+                            r_offset: rel.r_offset(endian).into(),
+                            symbol,
+                            r_type: rel.r_type(endian, is_mips64el),
+                            r_addend: rel.r_addend(endian).into(),
+                            delete: false,
+                        }
+                    })
+                    .collect()
+            } else {
+                Vec::new()
+            };
+            if let Some((dyns, link)) = section.dynamic(endian, data)? {
+                builder.dynamics.reserve(dyns.len());
+                let dynamic_strings = sections.strings(endian, data, link)?;
+                for d in dyns {
+                    let tag = d.d_tag(endian).into().try_into().map_err(|_| {
+                        Error(format!(
+                            "Unsupported dynamic tag 0x{:x}",
+                            d.d_tag(endian).into()
+                        ))
+                    })?;
+                    let val = d.d_val(endian).into();
+                    builder.dynamics.push(if d.is_string(endian) {
+                        let val = dynamic_strings
+                            .get(val.try_into().map_err(|_| {
+                                Error(format!("Unsupported dynamic string 0x{:x}", val))
+                            })?)
+                            .map_err(|_| Error(format!("Invalid dynamic string 0x{:x}", val)))?;
+                        Dynamic::String { tag, val }
+                    } else {
+                        Dynamic::Integer { tag, val }
+                    });
+                    if tag == elf::DT_NULL {
+                        break;
+                    }
+                }
+            }
+            if let Some(hash) = section.hash_header(endian, data)? {
+                builder.hash_bucket_count = hash.bucket_count.get(endian);
+            }
+            if let Some(hash) = section.gnu_hash_header(endian, data)? {
+                builder.gnu_hash_bloom_shift = hash.bloom_shift.get(endian);
+                builder.gnu_hash_bloom_count = hash.bloom_count.get(endian);
+                builder.gnu_hash_bucket_count = hash.bucket_count.get(endian);
+            }
+            if let Some(attributes) = section.gnu_attributes(endian, data)? {
+                let mut subsections = attributes.subsections()?;
+                while let Some(subsection) = subsections.next()? {
+                    let mut builder_subsection = AttributesSubsection::new(subsection.vendor());
+                    let mut subsubsections = subsection.subsubsections();
+                    while let Some(subsubsection) = subsubsections.next()? {
+                        let tag = match subsubsection.tag() {
+                            elf::Tag_File => AttributeTag::File,
+                            elf::Tag_Section => {
+                                let mut sections = Vec::new();
+                                let mut indices = subsubsection.indices();
+                                while let Some(index) = indices.next()? {
+                                    sections.push(SectionId(index as usize - 1));
+                                }
+                                AttributeTag::Section(sections)
+                            }
+                            elf::Tag_Symbol => {
+                                let mut symbols = Vec::new();
+                                let mut indices = subsubsection.indices();
+                                while let Some(index) = indices.next()? {
+                                    symbols.push(SymbolId(index as usize - 1));
+                                }
+                                AttributeTag::Symbol(symbols)
+                            }
+                            // FIXME
+                            _ => unimplemented!(),
+                        };
+                        let data = subsubsection.attributes_data();
+                        builder_subsection
+                            .subsubsections
+                            .push(AttributesSubsubsection { tag, data });
+                    }
+                    builder.gnu_attributes.subsections.push(builder_subsection);
+                }
+            }
+            let data = match section.sh_type(endian) {
+                elf::SHT_NOBITS => SectionData::UninitializedData(section.sh_size(endian).into()),
+                elf::SHT_PROGBITS | elf::SHT_NOTE | elf::SHT_INIT_ARRAY | elf::SHT_FINI_ARRAY => {
+                    SectionData::Data(section.data(endian, data)?)
+                }
+                elf::SHT_REL | elf::SHT_RELA => SectionData::Relocation,
+                elf::SHT_SYMTAB => {
+                    if index == symbols.section().0 {
+                        SectionData::Symbol
+                    } else {
+                        return Err(Error(format!(
+                            "Unsupported SHT_SYMTAB section at index {}",
+                            index
+                        )));
+                    }
+                }
+                elf::SHT_SYMTAB_SHNDX => {
+                    if index == symbols.shndx_section().0 {
+                        SectionData::SymbolSectionIndex
+                    } else {
+                        return Err(Error(format!(
+                            "Unsupported SHT_SYMTAB_SHNDX section at index {}",
+                            index
+                        )));
+                    }
+                }
+                elf::SHT_DYNSYM => {
+                    if index == dynamic_symbols.section().0 {
+                        SectionData::DynamicSymbol
+                    } else {
+                        return Err(Error(format!(
+                            "Unsupported SHT_DYNSYM section at index {}",
+                            index
+                        )));
+                    }
+                }
+                elf::SHT_STRTAB => {
+                    if index == shstrndx {
+                        builder.section_names = Some(id);
+                    }
+                    if index == symbols.string_section().0 {
+                        SectionData::String
+                    } else if index == dynamic_symbols.string_section().0 {
+                        SectionData::DynamicString
+                    } else if index == shstrndx {
+                        SectionData::SectionString
+                    } else {
+                        return Err(Error(format!(
+                            "Unsupported SHT_STRTAB section at index {}",
+                            index
+                        )));
+                    }
+                }
+                elf::SHT_DYNAMIC => SectionData::Dynamic,
+                elf::SHT_HASH => SectionData::Hash,
+                elf::SHT_GNU_HASH => SectionData::GnuHash,
+                elf::SHT_GNU_VERSYM => SectionData::GnuVersym,
+                elf::SHT_GNU_VERDEF => SectionData::GnuVerdef,
+                elf::SHT_GNU_VERNEED => SectionData::GnuVerneed,
+                elf::SHT_GNU_ATTRIBUTES => SectionData::GnuAttributes,
+                other => return Err(Error(format!("Unsupported section type {:x}", other))),
+            };
+            let sh_flags = section.sh_flags(endian).into();
+            let sh_link = section.sh_link(endian);
+            let sh_link_section = if sh_link == 0 {
+                None
+            } else {
+                Some(SectionId(sh_link as usize - 1))
+            };
+            let sh_info = section.sh_info(endian);
+            let sh_info_section = if sh_info == 0 || sh_flags & u64::from(elf::SHF_INFO_LINK) == 0 {
+                None
+            } else {
+                Some(SectionId(sh_info as usize - 1))
+            };
+            builder.sections.0.push(Section {
+                id,
+                // TODO
+                segment: None,
+                name: sections.section_name(endian, section)?,
+                sh_type: section.sh_type(endian),
+                sh_flags: section.sh_flags(endian).into(),
+                sh_addr: section.sh_addr(endian).into(),
+                sh_offset: section.sh_offset(endian).into() as usize,
+                sh_link_section,
+                sh_info,
+                sh_info_section,
+                sh_addralign: section.sh_addralign(endian).into() as usize,
+                sh_entsize: section.sh_entsize(endian).into(),
+                data,
+                // TODO
+                relocations,
+                delete: false,
+            });
+        }
+
+        for (id, symbol) in symbols.iter().skip(1).enumerate() {
+            builder.symbols.0.push(Symbol {
+                id: SymbolId(id),
+                name: symbols.symbol_name(endian, symbol)?,
+                // TODO
+                section: None,
+                st_info: symbol.st_info(),
+                st_other: symbol.st_other(),
+                st_shndx: symbol.st_shndx(endian),
+                st_value: symbol.st_value(endian).into(),
+                st_size: symbol.st_size(endian).into(),
+                version: VersionId::none(),
+                version_hidden: false,
+                delete: false,
+            });
+        }
+
+        for (id, symbol) in dynamic_symbols.iter().skip(1).enumerate() {
+            builder.dynamic_symbols.0.push(Symbol {
+                id: SymbolId(id),
+                name: dynamic_symbols.symbol_name(endian, symbol)?,
+                // TODO
+                section: None,
+                st_info: symbol.st_info(),
+                st_other: symbol.st_other(),
+                st_shndx: symbol.st_shndx(endian),
+                st_value: symbol.st_value(endian).into(),
+                st_size: symbol.st_size(endian).into(),
+                version: VersionId::global(),
+                version_hidden: false,
+                delete: false,
+            });
+        }
+
+        if let Some((versyms, link)) = gnu_versym {
+            if dynamic_symbols.section() != link || versyms.len() != dynamic_symbols.len() {
+                return Err(Error(format!("Invalid SHT_GNU_VERSYM section")));
+            }
+            let strings = dynamic_symbols.strings();
+
+            // TODO: can we derive max_index from versyms instead?
+            let mut max_index = 0;
+            if let Some((mut verdefs, link)) = gnu_verdef.clone() {
+                if dynamic_symbols.string_section() != link {
+                    return Err(Error(format!("Invalid SHT_GNU_VERDEF section")));
+                }
+                while let Some((verdef, _)) = verdefs.next()? {
+                    let index = verdef.vd_ndx.get(endian) & elf::VERSYM_VERSION;
+                    if max_index < index {
+                        max_index = index;
+                    }
+                }
+            }
+            if let Some((mut verneeds, link)) = gnu_verneed.clone() {
+                if dynamic_symbols.string_section() != link {
+                    return Err(Error(format!("Invalid SHT_GNU_VERNEED section")));
+                }
+                while let Some((_, mut vernauxs)) = verneeds.next()? {
+                    while let Some(vernaux) = vernauxs.next()? {
+                        let index = vernaux.vna_other.get(endian) & elf::VERSYM_VERSION;
+                        if max_index < index {
+                            max_index = index;
+                        }
+                    }
+                }
+            }
+
+            let mut ids = vec![VersionId::none(); max_index as usize + 1];
+
+            if let Some((mut verdefs, _)) = gnu_verdef {
+                while let Some((verdef, mut verdauxs)) = verdefs.next()? {
+                    let flags = verdef.vd_flags.get(endian);
+                    if flags & elf::VER_FLG_BASE != 0 {
+                        if flags != elf::VER_FLG_BASE
+                            || verdef.vd_ndx.get(endian) != 1
+                            || verdef.vd_cnt.get(endian) != 1
+                        {
+                            return Err(Error(format!(
+                                "Unsupported VER_FLG_BASE in SHT_GNU_VERDEF"
+                            )));
+                        }
+                        if builder.version_base.is_some() {
+                            return Err(Error(format!("Duplicate VER_FLG_BASE in SHT_GNU_VERDEF")));
+                        }
+                        let verdaux = verdauxs.next()?.ok_or_else(|| {
+                            Error(format!("Missing name for VER_FLG_BASE in SHT_GNU_VERDEF"))
+                        })?;
+                        builder.version_base = Some(verdaux.name(endian, strings)?);
+                        continue;
+                    }
+
+                    let index = verdef.vd_ndx.get(endian) & elf::VERSYM_VERSION;
+                    if ids[usize::from(index)] != VersionId::none() {
+                        return Err(Error(format!("Duplicate SHT_GNU_VERDEF index {}", index)));
+                    }
+                    let id = VersionId(builder.versions.0.len() + 2);
+                    ids[usize::from(index)] = id;
+
+                    let mut names = Vec::new();
+                    while let Some(verdaux) = verdauxs.next()? {
+                        names.push(verdaux.name(endian, strings)?);
+                    }
+
+                    builder
+                        .versions
+                        .0
+                        .push(Version::Def(VersionDef { id, flags, names }));
+                }
+            }
+
+            if let Some((mut verneeds, _)) = gnu_verneed {
+                while let Some((verneed, mut vernauxs)) = verneeds.next()? {
+                    let file = VersionFileId(builder.version_files.0.len());
+                    builder.version_files.0.push(VersionFile {
+                        id: file,
+                        name: verneed.file(endian, strings)?,
+                    });
+                    while let Some(vernaux) = vernauxs.next()? {
+                        let index = vernaux.vna_other.get(endian) & elf::VERSYM_VERSION;
+                        if ids[usize::from(index)] != VersionId::none() {
+                            return Err(Error(format!(
+                                "Duplicate SHT_GNU_VERNEED index {}",
+                                index
+                            )));
+                        }
+                        let id = VersionId(builder.versions.0.len() + 2);
+                        ids[usize::from(index)] = id;
+
+                        builder.versions.0.push(Version::Need(VersionNeed {
+                            id,
+                            flags: vernaux.vna_flags.get(endian),
+                            name: vernaux.name(endian, strings)?,
+                            file,
+                        }));
+                    }
+                }
+            }
+
+            for (id, versym) in versyms.iter().skip(1).enumerate() {
+                let index = versym.0.get(endian);
+                let symbol = &mut builder.dynamic_symbols.0[id];
+                symbol.version = *ids
+                    .get((index & elf::VERSYM_VERSION) as usize)
+                    .ok_or_else(|| Error(format!("Invalid SHT_GNU_VERSYM index {:x}", index)))?;
+                symbol.version_hidden = index & elf::VERSYM_HIDDEN != 0;
+            }
+        }
+
+        Ok(builder)
+    }
+
+    pub fn write(self, buffer: &mut dyn WritableBuffer) -> Result<()> {
+        struct SectionOut {
+            id: SectionId,
+            name: Option<write::StringId>,
+            offset: usize,
+        }
+
+        struct DynamicOut {
+            string: Option<write::StringId>,
+        }
+
+        struct SymbolOut {
+            id: SymbolId,
+            name: Option<write::StringId>,
+        }
+
+        struct DynamicSymbolOut {
+            id: SymbolId,
+            name: Option<write::StringId>,
+            hash: Option<u32>,
+            gnu_hash: Option<u32>,
+        }
+
+        #[derive(Default, Clone)]
+        struct VersionFileOut {
+            versions: Vec<VersionId>,
+        }
+
+        let mut writer = write::elf::Writer::new(self.endian, self.is_64, buffer);
+
+        // Find metadata sections, and assign section indices.
+        let mut shstrtab_id = None;
+        let mut symtab_id = None;
+        let mut symtab_shndx_id = None;
+        let mut strtab_id = None;
+        let mut dynsym_id = None;
+        let mut dynstr_id = None;
+        let mut dynamic_id = None;
+        let mut hash_id = None;
+        let mut gnu_hash_id = None;
+        let mut gnu_versym_id = None;
+        let mut gnu_verdef_id = None;
+        let mut gnu_verneed_id = None;
+        let mut gnu_attributes_id = None;
+        let mut out_sections = Vec::with_capacity(self.sections.0.len());
+        let mut out_sections_index = Vec::with_capacity(self.sections.0.len());
+        if !self.sections.0.is_empty() {
+            writer.reserve_null_section_index();
+        }
+        for section in &self.sections.0 {
+            if section.delete {
+                out_sections_index.push(None);
+                continue;
+            }
+
+            let index = match &section.data {
+                SectionData::Data(_)
+                | SectionData::UninitializedData(_)
+                | SectionData::Relocation => writer.reserve_section_index(),
+                SectionData::SectionString => {
+                    if shstrtab_id.is_some() {
+                        return Err(Error(format!("Multiple .shstrtab sections")));
+                    }
+                    shstrtab_id = Some(section.id);
+                    writer.reserve_shstrtab_section_index()
+                }
+                SectionData::Symbol => {
+                    if symtab_id.is_some() {
+                        return Err(Error(format!("Multiple .symtab sections")));
+                    }
+                    symtab_id = Some(section.id);
+                    writer.reserve_symtab_section_index()
+                }
+                SectionData::SymbolSectionIndex => {
+                    if symtab_shndx_id.is_some() {
+                        return Err(Error(format!("Multiple .symtab_shndx sections")));
+                    }
+                    symtab_shndx_id = Some(section.id);
+                    writer.reserve_symtab_shndx_section_index()
+                }
+                SectionData::String => {
+                    if strtab_id.is_some() {
+                        return Err(Error(format!("Multiple .strtab sections")));
+                    }
+                    strtab_id = Some(section.id);
+                    writer.reserve_strtab_section_index()
+                }
+                SectionData::Dynamic => {
+                    if dynamic_id.is_some() {
+                        return Err(Error(format!("Multiple .dynamic sections")));
+                    }
+                    dynamic_id = Some(section.id);
+                    writer.reserve_dynamic_section_index()
+                }
+                SectionData::DynamicSymbol => {
+                    if dynsym_id.is_some() {
+                        return Err(Error(format!("Multiple .dynsym sections")));
+                    }
+                    dynsym_id = Some(section.id);
+                    writer.reserve_dynsym_section_index()
+                }
+                SectionData::DynamicString => {
+                    if dynstr_id.is_some() {
+                        return Err(Error(format!("Multiple .dynstr sections")));
+                    }
+                    dynstr_id = Some(section.id);
+                    writer.reserve_dynstr_section_index()
+                }
+                SectionData::Hash => {
+                    if hash_id.is_some() {
+                        return Err(Error(format!("Multiple .hash sections")));
+                    }
+                    hash_id = Some(section.id);
+                    writer.reserve_hash_section_index()
+                }
+                SectionData::GnuHash => {
+                    if gnu_hash_id.is_some() {
+                        return Err(Error(format!("Multiple .gnu.hash sections")));
+                    }
+                    gnu_hash_id = Some(section.id);
+                    writer.reserve_gnu_hash_section_index()
+                }
+                SectionData::GnuVersym => {
+                    if gnu_versym_id.is_some() {
+                        return Err(Error(format!("Multiple .gnu.version sections")));
+                    }
+                    gnu_versym_id = Some(section.id);
+                    writer.reserve_gnu_versym_section_index()
+                }
+                SectionData::GnuVerdef => {
+                    if gnu_verdef_id.is_some() {
+                        return Err(Error(format!("Multiple .gnu.version_d sections")));
+                    }
+                    gnu_verdef_id = Some(section.id);
+                    writer.reserve_gnu_verdef_section_index()
+                }
+                SectionData::GnuVerneed => {
+                    if gnu_verneed_id.is_some() {
+                        return Err(Error(format!("Multiple .gnu.version_r sections")));
+                    }
+                    gnu_verneed_id = Some(section.id);
+                    writer.reserve_gnu_verneed_section_index()
+                }
+                SectionData::GnuAttributes => {
+                    if gnu_attributes_id.is_some() {
+                        return Err(Error(format!("Multiple .gnu.attributes sections")));
+                    }
+                    gnu_attributes_id = Some(section.id);
+                    writer.reserve_gnu_attributes_section_index()
+                }
+            };
+            out_sections_index.push(Some(index));
+
+            let name = if section.name.is_empty() {
+                None
+            } else {
+                // TODO: this is ignored for special sections
+                Some(writer.add_section_name(section.name))
+            };
+            out_sections.push(SectionOut {
+                id: section.id,
+                name,
+                offset: 0,
+            });
+        }
+
+        // Assign dynamic strings.
+        let mut out_dynamics = Vec::new();
+        if dynamic_id.is_some() {
+            out_dynamics.reserve(self.dynamics.len());
+            for dynamic in &self.dynamics {
+                let string = match dynamic {
+                    Dynamic::Integer { .. } => None,
+                    Dynamic::String { val, .. } => Some(writer.add_dynamic_string(val)),
+                };
+                out_dynamics.push(DynamicOut { string });
+            }
+        }
+
+        // Assign dynamic symbol indices.
+        let mut out_dynsyms = Vec::new();
+        if dynsym_id.is_some() {
+            out_dynsyms.reserve(self.dynamic_symbols.0.len());
+            for symbol in &self.dynamic_symbols {
+                if symbol.delete {
+                    continue;
+                }
+                // Skip symbols for deleted sections.
+                if let Some(section) = symbol.section {
+                    if out_sections_index[section.0].is_none() {
+                        continue;
+                    }
+                }
+
+                let mut name = None;
+                let mut hash = None;
+                let mut gnu_hash = None;
+                if !symbol.name.is_empty() {
+                    name = Some(writer.add_dynamic_string(symbol.name));
+                    if hash_id.is_some() {
+                        hash = Some(elf::hash(symbol.name));
+                    }
+                    if gnu_hash_id.is_some() && symbol.st_shndx != elf::SHN_UNDEF {
+                        gnu_hash = Some(elf::gnu_hash(symbol.name));
+                    }
+                }
+                out_dynsyms.push(DynamicSymbolOut {
+                    id: symbol.id,
+                    name,
+                    hash,
+                    gnu_hash,
+                });
+            }
+        }
+        // We must sort for GNU hash before allocating symbol indices.
+        if gnu_hash_id.is_some() {
+            if self.gnu_hash_bucket_count == 0 {
+                return Err(Error(format!(".gnu.hash bucket count is zero")));
+            }
+            // TODO: recalculate bucket_count?
+            out_dynsyms.sort_by_key(|sym| match sym.gnu_hash {
+                None => (0, 0),
+                Some(hash) => (1, hash % self.gnu_hash_bucket_count),
+            });
+        }
+        let mut out_dynsyms_index = vec![None; self.dynamic_symbols.0.len()];
+        for out_dynsym in out_dynsyms.iter_mut() {
+            out_dynsyms_index[out_dynsym.id.0] = Some(writer.reserve_dynamic_symbol_index());
+        }
+
+        // Hash parameters.
+        let hash_index_base = out_dynsyms
+            .first()
+            .map(|sym| out_dynsyms_index[sym.id.0].unwrap().0)
+            .unwrap_or(0);
+        let hash_chain_count = writer.dynamic_symbol_count();
+
+        // GNU hash parameters.
+        let gnu_hash_index_base = out_dynsyms
+            .iter()
+            .position(|sym| sym.gnu_hash.is_some())
+            .unwrap_or(0);
+        let gnu_hash_symbol_base = out_dynsyms
+            .iter()
+            .find(|sym| sym.gnu_hash.is_some())
+            .map(|sym| out_dynsyms_index[sym.id.0].unwrap().0)
+            .unwrap_or_else(|| writer.dynamic_symbol_count());
+        let gnu_hash_symbol_count = writer.dynamic_symbol_count() - gnu_hash_symbol_base;
+
+        // Assign symbol indices.
+        let mut out_syms = Vec::with_capacity(self.symbols.0.len());
+        if symtab_id.is_some() {
+            // Local symbols must come before global.
+            let local_symbols = self
+                .symbols
+                .into_iter()
+                .filter(|symbol| symbol.st_bind() == elf::STB_LOCAL);
+            let global_symbols = self
+                .symbols
+                .into_iter()
+                .filter(|symbol| symbol.st_bind() != elf::STB_LOCAL);
+            for symbol in local_symbols.chain(global_symbols) {
+                if symbol.delete {
+                    continue;
+                }
+                // Skip symbols for deleted sections.
+                if let Some(section) = symbol.section {
+                    if out_sections_index[section.0].is_none() {
+                        continue;
+                    }
+                }
+
+                let name = if symbol.name.is_empty() {
+                    None
+                } else {
+                    Some(writer.add_string(symbol.name))
+                };
+
+                out_syms.push(SymbolOut {
+                    id: symbol.id,
+                    name,
+                });
+            }
+        }
+        let num_local = 1 + out_syms
+            .iter()
+            .take_while(|sym| self.symbols.0[sym.id.0].st_bind() == elf::STB_LOCAL)
+            .count() as u32;
+        let mut out_syms_index = vec![Default::default(); self.symbols.0.len()];
+        for out_sym in out_syms.iter_mut() {
+            // FIXME: symtab_shndx handling
+            out_syms_index[out_sym.id.0] = Some(writer.reserve_symbol_index(None));
+        }
+
+        // Count the versions and add version strings.
+        // TODO: omit unused versions
+        let mut verdef_count = 0;
+        let mut verdaux_count = 0;
+        let mut verneed_count = 0;
+        let mut vernaux_count = 0;
+        let mut out_version_files = vec![VersionFileOut::default(); self.version_files.0.len()];
+        if let Some(version_base) = self.version_base {
+            verdef_count += 1;
+            verdaux_count += 1;
+            writer.add_dynamic_string(version_base);
+        }
+        for version in &self.versions.0 {
+            match version {
+                Version::Def(def) => {
+                    verdef_count += 1;
+                    verdaux_count += def.names.len();
+                    for name in &def.names {
+                        writer.add_dynamic_string(name);
+                    }
+                }
+                Version::Need(need) => {
+                    vernaux_count += 1;
+                    writer.add_dynamic_string(need.name);
+                    out_version_files[need.file.0].versions.push(need.id);
+                }
+            }
+        }
+        for file in &self.version_files.0 {
+            if out_version_files[file.id.0].versions.is_empty() {
+                continue;
+            }
+            verneed_count += 1;
+            writer.add_dynamic_string(file.name);
+        }
+
+        // Build the GNU attributes section.
+        let mut gnu_attributes = Vec::new();
+        if !self.gnu_attributes.subsections.is_empty() {
+            let mut writer = writer.attributes_writer();
+            for subsection in &self.gnu_attributes.subsections {
+                writer.start_subsection(subsection.vendor);
+                for subsubsection in &subsection.subsubsections {
+                    writer.start_subsubsection(subsubsection.tag.tag());
+                    match &subsubsection.tag {
+                        AttributeTag::File => {}
+                        AttributeTag::Section(sections) => {
+                            for id in sections {
+                                if let Some(index) = out_sections_index[id.0] {
+                                    writer.write_subsubsection_index(index.0);
+                                }
+                            }
+                            writer.write_subsubsection_index(0);
+                        }
+                        AttributeTag::Symbol(symbols) => {
+                            for id in symbols {
+                                if let Some(index) = out_syms_index[id.0] {
+                                    writer.write_subsubsection_index(index.0);
+                                }
+                            }
+                            writer.write_subsubsection_index(0);
+                        }
+                    }
+                    writer.write_subsubsection_attributes(subsubsection.data);
+                    writer.end_subsubsection();
+                }
+                writer.end_subsection();
+            }
+            gnu_attributes = writer.data();
+            assert_ne!(gnu_attributes.len(), 0);
+        }
+
+        // Start reserving file ranges.
+        writer.reserve_file_header();
+
+        let mut hash_addr = 0;
+        let mut gnu_hash_addr = 0;
+        let mut versym_addr = 0;
+        let mut verdef_addr = 0;
+        let mut verneed_addr = 0;
+        let mut dynamic_addr = 0;
+        let mut dynsym_addr = 0;
+        let mut dynstr_addr = 0;
+
+        if !self.segments.0.is_empty() {
+            // TODO: support program headers in other locations.
+            if self.e_phoff != writer.reserved_len() {
+                return Err(Error(format!(
+                    "Unsupported e_phoff value 0x{:x}",
+                    self.e_phoff
+                )));
+            }
+            let num_segments = self
+                .segments
+                .0
+                .iter()
+                .filter(|segment| !segment.delete)
+                .count();
+            writer.reserve_program_headers(num_segments as u32);
+        }
+
+        let mut alloc_sections = Vec::new();
+        if !self.segments.0.is_empty() {
+            // Reserve alloc sections at original offsets.
+            alloc_sections = self
+                .sections
+                .0
+                .iter()
+                .filter(|section| section.sh_flags & u64::from(elf::SHF_ALLOC) != 0)
+                .collect();
+            // The data for alloc sections may need to be written in a different order
+            // from their section headers.
+            alloc_sections.sort_by_key(|section| section.sh_offset);
+            for section in &alloc_sections {
+                if section.sh_offset < writer.reserved_len() {
+                    return Err(Error(format!(
+                        "Unsupported sh_offset value 0x{:x}, expected at least 0x{:x}",
+                        section.sh_offset,
+                        writer.reserved_len(),
+                    )));
+                }
+                // The input sh_offset needs to be preserved so that offsets in program
+                // headers are correct.
+                writer.reserve_until(section.sh_offset);
+                let offset = match &section.data {
+                    SectionData::Data(data) => writer.reserve(data.len(), section.sh_addralign),
+                    SectionData::UninitializedData(_) => {
+                        // Note: unaligned input sh_offset was observed in practice.
+                        writer.reserve(0, 1)
+                    }
+                    SectionData::Relocation => writer.reserve_relocations(
+                        section.relocations.len(),
+                        section.sh_type == elf::SHT_RELA,
+                    ),
+                    SectionData::Dynamic => {
+                        dynamic_addr = section.sh_addr;
+                        writer.reserve_dynamic(self.dynamics.len())
+                    }
+                    SectionData::DynamicSymbol => {
+                        dynsym_addr = section.sh_addr;
+                        writer.reserve_dynsym()
+                    }
+                    SectionData::DynamicString => {
+                        dynstr_addr = section.sh_addr;
+                        writer.reserve_dynstr()
+                    }
+                    SectionData::Hash => {
+                        hash_addr = section.sh_addr;
+                        writer.reserve_hash(self.hash_bucket_count, hash_chain_count)
+                    }
+                    SectionData::GnuHash => {
+                        gnu_hash_addr = section.sh_addr;
+                        writer.reserve_gnu_hash(
+                            self.gnu_hash_bloom_count,
+                            self.gnu_hash_bucket_count,
+                            gnu_hash_symbol_count,
+                        )
+                    }
+                    SectionData::GnuVersym => {
+                        versym_addr = section.sh_addr;
+                        writer.reserve_gnu_versym()
+                    }
+                    SectionData::GnuVerdef => {
+                        verdef_addr = section.sh_addr;
+                        writer.reserve_gnu_verdef(verdef_count, verdaux_count)
+                    }
+                    SectionData::GnuVerneed => {
+                        verneed_addr = section.sh_addr;
+                        writer.reserve_gnu_verneed(verneed_count, vernaux_count)
+                    }
+                    _ => {
+                        return Err(Error(format!(
+                            "Unsupported alloc section type {:x}",
+                            section.sh_type
+                        )));
+                    }
+                };
+                if section.sh_offset != offset {
+                    return Err(Error(format!(
+                        "Unaligned sh_offset value 0x{:x}",
+                        section.sh_offset
+                    )));
+                }
+                out_sections[section.id.0].offset = offset;
+            }
+        }
+
+        // Reserve non-alloc sections at any offset.
+        for section in &self.sections.0 {
+            if !self.segments.0.is_empty() && section.sh_flags & u64::from(elf::SHF_ALLOC) != 0 {
+                continue;
+            }
+            match &section.data {
+                SectionData::Data(data) => {
+                    out_sections[section.id.0].offset =
+                        writer.reserve(data.len(), section.sh_addralign);
+                }
+                SectionData::UninitializedData(_) => {
+                    out_sections[section.id.0].offset = writer.reserve(0, section.sh_addralign);
+                }
+                SectionData::GnuAttributes => {
+                    writer.reserve_gnu_attributes(gnu_attributes.len());
+                }
+                // FIXME
+                _ => {}
+            }
+        }
+
+        writer.reserve_symtab();
+        writer.reserve_symtab_shndx();
+        writer.reserve_strtab();
+
+        // Reserve non-alloc relocations.
+        for section in &self.sections.0 {
+            if !self.segments.0.is_empty() && section.sh_flags & u64::from(elf::SHF_ALLOC) != 0 {
+                continue;
+            }
+            match section.data {
+                SectionData::Relocation => {}
+                _ => continue,
+            }
+            // FIXME: deleted symbols
+            out_sections[section.id.0].offset = writer
+                .reserve_relocations(section.relocations.len(), section.sh_type == elf::SHT_RELA);
+        }
+
+        writer.reserve_shstrtab();
+        writer.reserve_section_headers();
+
+        // Start writing.
+        writer.write_file_header(&write::elf::FileHeader {
+            os_abi: self.os_abi,
+            abi_version: self.abi_version,
+            e_type: self.e_type,
+            e_machine: self.e_machine,
+            e_entry: self.e_entry,
+            e_flags: self.e_flags,
+        })?;
+
+        if !self.segments.0.is_empty() {
+            writer.write_align_program_headers();
+            for segment in &self.segments.0 {
+                if segment.delete {
+                    continue;
+                }
+                writer.write_program_header(&write::elf::ProgramHeader {
+                    p_type: segment.p_type,
+                    p_flags: segment.p_flags,
+                    p_offset: segment.p_offset,
+                    p_vaddr: segment.p_vaddr,
+                    p_paddr: segment.p_paddr,
+                    p_filesz: segment.p_filesz,
+                    p_memsz: segment.p_memsz,
+                    p_align: segment.p_align,
+                });
+            }
+        }
+
+        // Write alloc sections.
+        if !self.segments.0.is_empty() {
+            for section in alloc_sections {
+                writer.pad_until(section.sh_offset);
+                match &section.data {
+                    SectionData::Data(data) => {
+                        debug_assert_eq!(out_sections[section.id.0].offset, writer.len());
+                        writer.write(data);
+                    }
+                    SectionData::UninitializedData(_) => {}
+                    SectionData::Relocation => {
+                        writer.write_align_relocation();
+                        for rel in &section.relocations {
+                            let r_sym = if let Some(symbol) = rel.symbol {
+                                // FIXME: deleted symbol
+                                out_dynsyms_index[symbol.0].unwrap().0
+                            } else {
+                                0
+                            };
+                            writer.write_relocation(
+                                true,
+                                &write::elf::Rel {
+                                    r_offset: rel.r_offset,
+                                    r_sym,
+                                    r_type: rel.r_type,
+                                    r_addend: rel.r_addend,
+                                },
+                            );
+                        }
+                    }
+                    SectionData::Dynamic => {
+                        for (d, out) in self.dynamics.iter().zip(out_dynamics.iter()) {
+                            match *d {
+                                Dynamic::Integer { tag, val } => {
+                                    // TODO: fix values?
+                                    writer.write_dynamic(tag, val);
+                                }
+                                Dynamic::String { tag, .. } => {
+                                    writer.write_dynamic_string(tag, out.string.unwrap());
+                                }
+                            }
+                        }
+                    }
+                    SectionData::DynamicSymbol => {
+                        writer.write_null_dynamic_symbol();
+                        for out_sym in &out_dynsyms {
+                            let symbol = &self.dynamic_symbols.0[out_sym.id.0];
+                            let section =
+                                symbol.section.map(|id| out_sections_index[id.0].unwrap());
+                            writer.write_dynamic_symbol(&write::elf::Sym {
+                                name: out_sym.name,
+                                section,
+                                st_info: symbol.st_info,
+                                st_other: symbol.st_other,
+                                st_shndx: symbol.st_shndx,
+                                st_value: symbol.st_value,
+                                st_size: symbol.st_size,
+                            });
+                        }
+                    }
+                    SectionData::DynamicString => {
+                        writer.write_dynstr();
+                    }
+                    SectionData::Hash => {
+                        if self.hash_bucket_count == 0 {
+                            return Err(Error(format!(".hash bucket count is zero")));
+                        }
+                        writer.write_hash(self.hash_bucket_count, hash_chain_count, |index| {
+                            out_dynsyms
+                                .get(index.checked_sub(hash_index_base)? as usize)?
+                                .hash
+                        });
+                    }
+                    SectionData::GnuHash => {
+                        if self.gnu_hash_bucket_count == 0 {
+                            return Err(Error(format!(".gnu.hash bucket count is zero")));
+                        }
+                        writer.write_gnu_hash(
+                            gnu_hash_symbol_base,
+                            self.gnu_hash_bloom_shift,
+                            self.gnu_hash_bloom_count,
+                            self.gnu_hash_bucket_count,
+                            gnu_hash_symbol_count,
+                            |index| {
+                                out_dynsyms[gnu_hash_index_base + index as usize]
+                                    .gnu_hash
+                                    .unwrap()
+                            },
+                        );
+                    }
+                    SectionData::GnuVersym => {
+                        writer.write_null_gnu_versym();
+                        for out_dynsym in &out_dynsyms {
+                            let symbol = &self.dynamic_symbols.0[out_dynsym.id.0];
+                            let mut index = symbol.version.0 as u16;
+                            if symbol.version_hidden {
+                                index |= elf::VERSYM_HIDDEN;
+                            }
+                            writer.write_gnu_versym(index);
+                        }
+                    }
+                    SectionData::GnuVerdef => {
+                        writer.write_align_gnu_verdef();
+                        if let Some(version_base) = self.version_base {
+                            writer.write_gnu_verdef(&write::elf::Verdef {
+                                version: elf::VER_DEF_CURRENT,
+                                flags: elf::VER_FLG_BASE,
+                                index: 1,
+                                aux_count: 1,
+                                name: writer.get_dynamic_string(version_base),
+                            });
+                        }
+                        for version in &self.versions {
+                            if let Version::Def(def) = version {
+                                let mut names = def.names.iter();
+                                let name = names.next().ok_or_else(|| {
+                                    Error(format!("Missing SHT_GNU_VERDEF name {}", def.id.0))
+                                })?;
+                                writer.write_gnu_verdef(&write::elf::Verdef {
+                                    version: elf::VER_DEF_CURRENT,
+                                    flags: def.flags,
+                                    index: def.id.0 as u16,
+                                    aux_count: def.names.len() as u16,
+                                    name: writer.get_dynamic_string(name),
+                                });
+                                for name in names {
+                                    writer.write_gnu_verdaux(writer.get_dynamic_string(name));
+                                }
+                            }
+                        }
+                    }
+                    SectionData::GnuVerneed => {
+                        writer.write_align_gnu_verneed();
+                        for file in &self.version_files.0 {
+                            let out_file = &out_version_files[file.id.0];
+                            if out_file.versions.is_empty() {
+                                continue;
+                            }
+                            writer.write_gnu_verneed(&write::elf::Verneed {
+                                version: elf::VER_NEED_CURRENT,
+                                aux_count: out_file.versions.len() as u16,
+                                file: writer.get_dynamic_string(file.name),
+                            });
+                            for id in &out_file.versions {
+                                // This will always match.
+                                if let Version::Need(need) = &self.versions.0[id.0 - 2] {
+                                    debug_assert_eq!(*id, need.id);
+                                    writer.write_gnu_vernaux(&write::elf::Vernaux {
+                                        flags: need.flags,
+                                        index: need.id.0 as u16,
+                                        name: writer.get_dynamic_string(need.name),
+                                    });
+                                }
+                            }
+                        }
+                    }
+                    _ => {
+                        return Err(Error(format!(
+                            "Unsupported alloc section type {:x}",
+                            section.sh_type
+                        )));
+                    }
+                }
+            }
+        }
+
+        // Write non-alloc sections.
+        for section in &self.sections.0 {
+            if !self.segments.0.is_empty() && section.sh_flags & u64::from(elf::SHF_ALLOC) != 0 {
+                continue;
+            }
+            match &section.data {
+                SectionData::Data(data) => {
+                    writer.write_align(section.sh_addralign);
+                    debug_assert_eq!(out_sections[section.id.0].offset, writer.len());
+                    writer.write(data);
+                }
+                SectionData::GnuAttributes => {
+                    writer.write_gnu_attributes(&gnu_attributes);
+                }
+                _ => {}
+            }
+        }
+
+        writer.write_null_symbol();
+        for out_sym in &out_syms {
+            let symbol = &self.symbols.0[out_sym.id.0];
+            let section = symbol.section.map(|id| out_sections_index[id.0].unwrap());
+            writer.write_symbol(&write::elf::Sym {
+                name: out_sym.name,
+                section,
+                st_info: symbol.st_info,
+                st_other: symbol.st_other,
+                st_shndx: symbol.st_shndx,
+                st_value: symbol.st_value,
+                st_size: symbol.st_size,
+            });
+        }
+        writer.write_symtab_shndx();
+        writer.write_strtab();
+
+        // Write non-alloc relocations.
+        for section in &self.sections.0 {
+            if !self.segments.0.is_empty() && section.sh_flags & u64::from(elf::SHF_ALLOC) != 0 {
+                continue;
+            }
+            match section.data {
+                SectionData::Relocation => {}
+                _ => continue,
+            }
+            let out_syms = if section.sh_link_section.is_none() {
+                // FIXME: error
+                continue;
+            } else if section.sh_link_section == symtab_id {
+                &out_syms_index
+            } else if section.sh_link_section == symtab_id {
+                &out_dynsyms_index
+            } else {
+                // FIXME: error
+                continue;
+            };
+            writer.write_align_relocation();
+            for rel in &section.relocations {
+                let r_sym = if let Some(symbol) = rel.symbol {
+                    // FIXME: deleted symbol
+                    out_syms[symbol.0].unwrap().0
+                } else {
+                    0
+                };
+                writer.write_relocation(
+                    true,
+                    &write::elf::Rel {
+                        r_offset: rel.r_offset,
+                        r_sym,
+                        r_type: rel.r_type,
+                        r_addend: rel.r_addend,
+                    },
+                );
+            }
+        }
+
+        writer.write_shstrtab();
+
+        writer.write_null_section_header();
+        for out_section in &out_sections {
+            let section = &self.sections.0[out_section.id.0];
+            match &section.data {
+                SectionData::Data(_)
+                | SectionData::UninitializedData(_)
+                | SectionData::Relocation => {
+                    let sh_size = match section.data {
+                        SectionData::Data(ref data) => data.len() as u64,
+                        SectionData::UninitializedData(len) => len,
+                        SectionData::Relocation => writer.relocations_size(
+                            section.relocations.len(),
+                            section.sh_type == elf::SHT_RELA,
+                        ) as u64,
+                        _ => 0,
+                    };
+                    let sh_link = if let Some(id) = section.sh_link_section {
+                        // FIXME: error handling
+                        out_sections_index[id.0].unwrap().0
+                    } else {
+                        0
+                    };
+                    let sh_info = if let Some(id) = section.sh_info_section {
+                        // FIXME: error handling
+                        out_sections_index[id.0].unwrap().0
+                    } else {
+                        section.sh_info
+                    };
+                    writer.write_section_header(&write::elf::SectionHeader {
+                        name: out_section.name,
+                        sh_type: section.sh_type,
+                        sh_flags: section.sh_flags,
+                        sh_addr: section.sh_addr,
+                        sh_offset: out_section.offset as u64,
+                        sh_size,
+                        sh_link,
+                        sh_info,
+                        sh_addralign: section.sh_addralign as u64,
+                        sh_entsize: section.sh_entsize,
+                    });
+                }
+                SectionData::SectionString => {
+                    writer.write_shstrtab_section_header();
+                }
+                SectionData::Symbol => {
+                    writer.write_symtab_section_header(num_local);
+                }
+                SectionData::SymbolSectionIndex => {
+                    writer.write_symtab_shndx_section_header();
+                }
+                SectionData::String => {
+                    writer.write_strtab_section_header();
+                }
+                SectionData::Dynamic => {
+                    writer.write_dynamic_section_header(dynamic_addr);
+                }
+                SectionData::DynamicString => {
+                    writer.write_dynstr_section_header(dynstr_addr);
+                }
+                SectionData::DynamicSymbol => {
+                    writer.write_dynsym_section_header(dynsym_addr, 1);
+                }
+                SectionData::Hash => {
+                    writer.write_hash_section_header(hash_addr);
+                }
+                SectionData::GnuHash => {
+                    writer.write_gnu_hash_section_header(gnu_hash_addr);
+                }
+                SectionData::GnuVersym => {
+                    writer.write_gnu_versym_section_header(versym_addr);
+                }
+                SectionData::GnuVerdef => {
+                    writer.write_gnu_verdef_section_header(verdef_addr);
+                }
+                SectionData::GnuVerneed => {
+                    writer.write_gnu_verneed_section_header(verneed_addr);
+                }
+                SectionData::GnuAttributes => {
+                    writer.write_gnu_attributes_section_header();
+                }
+            }
+        }
+        debug_assert_eq!(writer.reserved_len(), writer.len());
+        Ok(())
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SegmentId(usize);
+
+#[derive(Debug)]
+pub struct Segment<'data> {
+    id: SegmentId,
+    pub p_type: u32,
+    pub p_flags: u32,
+    pub p_offset: u64,
+    pub p_vaddr: u64,
+    pub p_paddr: u64,
+    pub p_filesz: u64,
+    pub p_memsz: u64,
+    pub p_align: u64,
+
+    pub delete: bool,
+
+    // Might need to reference data if no sections.
+    marker: PhantomData<&'data ()>,
+}
+
+impl<'data> Segment<'data> {
+    pub fn id(&self) -> SegmentId {
+        self.id
+    }
+}
+
+#[derive(Debug)]
+pub struct Segments<'data>(Vec<Segment<'data>>);
+
+impl<'data> Segments<'data> {
+    fn new() -> Self {
+        Segments(Vec::new())
+    }
+
+    pub fn add(&mut self) -> &mut Segment<'data> {
+        let id = SegmentId(self.0.len());
+        self.0.push(Segment {
+            id,
+            p_type: 0,
+            p_flags: 0,
+            p_offset: 0,
+            p_vaddr: 0,
+            p_paddr: 0,
+            p_filesz: 0,
+            p_memsz: 0,
+            p_align: 0,
+            delete: false,
+            marker: PhantomData,
+        });
+        self.0.last_mut().unwrap()
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SectionId(usize);
+
+#[derive(Debug)]
+pub struct Section<'data> {
+    id: SectionId,
+    pub segment: Option<SegmentId>,
+    pub name: &'data [u8],
+    pub sh_type: u32,
+    pub sh_flags: u64,
+    pub sh_addr: u64,
+    pub sh_offset: usize,
+    pub sh_link_section: Option<SectionId>,
+    pub sh_info: u32,
+    pub sh_info_section: Option<SectionId>,
+    pub sh_addralign: usize,
+    pub sh_entsize: u64,
+
+    pub data: SectionData<'data>,
+    pub relocations: Vec<Relocation>,
+    pub delete: bool,
+}
+
+impl<'data> Section<'data> {
+    pub fn id(&self) -> SectionId {
+        self.id
+    }
+}
+
+#[derive(Debug)]
+pub enum SectionData<'data> {
+    Data(&'data [u8]),
+    UninitializedData(u64),
+    Relocation,
+    SectionString,
+    Symbol,
+    SymbolSectionIndex,
+    String,
+    Dynamic,
+    DynamicSymbol,
+    DynamicString,
+    Hash,
+    GnuHash,
+    GnuVersym,
+    GnuVerdef,
+    GnuVerneed,
+    GnuAttributes,
+}
+
+#[derive(Debug)]
+pub struct Sections<'data>(Vec<Section<'data>>);
+
+impl<'data> Sections<'data> {
+    fn new() -> Self {
+        Sections(Vec::new())
+    }
+}
+
+// include dynamic:bool?
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct SymbolId(usize);
+
+#[derive(Debug)]
+pub struct Symbol<'data> {
+    id: SymbolId,
+    pub name: &'data [u8],
+    pub section: Option<SectionId>,
+    pub st_info: u8,
+    pub st_other: u8,
+    pub st_shndx: u16,
+    pub st_value: u64,
+    pub st_size: u64,
+    pub delete: bool,
+    /// Version for dynamic symbols.
+    pub version: VersionId,
+    pub version_hidden: bool,
+}
+
+impl<'data> Symbol<'data> {
+    /// Get the `st_bind` component of the `st_info` field.
+    #[inline]
+    pub fn st_bind(&self) -> u8 {
+        self.st_info >> 4
+    }
+
+    /// Get the `st_type` component of the `st_info` field.
+    #[inline]
+    pub fn st_type(&self) -> u8 {
+        self.st_info & 0xf
+    }
+
+    /// Set the `st_info` field given the `st_bind` and `st_type` components.
+    #[inline]
+    pub fn set_st_info(&mut self, st_bind: u8, st_type: u8) {
+        self.st_info = (st_bind << 4) + (st_type & 0xf);
+    }
+}
+
+#[derive(Debug)]
+pub struct Symbols<'data>(Vec<Symbol<'data>>);
+
+impl<'data> Symbols<'data> {
+    fn new() -> Self {
+        Symbols(Vec::new())
+    }
+}
+
+impl<'a, 'data> IntoIterator for &'a Symbols<'data> {
+    type Item = &'a Symbol<'data>;
+    type IntoIter = core::slice::Iter<'a, Symbol<'data>>;
+    fn into_iter(self) -> core::slice::Iter<'a, Symbol<'data>> {
+        self.0.as_slice().into_iter()
+    }
+}
+
+impl<'a, 'data> IntoIterator for &'a mut Symbols<'data> {
+    type Item = &'a mut Symbol<'data>;
+    type IntoIter = core::slice::IterMut<'a, Symbol<'data>>;
+    fn into_iter(self) -> core::slice::IterMut<'a, Symbol<'data>> {
+        self.0.as_mut_slice().into_iter()
+    }
+}
+
+#[derive(Debug)]
+pub struct Relocation {
+    pub r_offset: u64,
+    pub symbol: Option<SymbolId>,
+    pub r_type: u32,
+    pub r_addend: i64,
+    pub delete: bool,
+}
+
+#[derive(Debug)]
+pub enum Dynamic<'data> {
+    Integer { tag: u32, val: u64 },
+    String { tag: u32, val: &'data [u8] },
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct VersionFileId(usize);
+
+#[derive(Debug)]
+pub struct VersionFile<'data> {
+    id: VersionFileId,
+    pub name: &'data [u8],
+}
+
+#[derive(Debug)]
+pub struct VersionFiles<'data>(Vec<VersionFile<'data>>);
+
+impl<'data> VersionFiles<'data> {
+    fn new() -> Self {
+        VersionFiles(Vec::new())
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct VersionId(usize);
+
+impl VersionId {
+    pub fn none() -> Self {
+        VersionId(0)
+    }
+
+    pub fn global() -> Self {
+        VersionId(1)
+    }
+}
+
+#[derive(Debug)]
+pub enum Version<'data> {
+    Def(VersionDef<'data>),
+    Need(VersionNeed<'data>),
+}
+
+impl<'data> Version<'data> {
+    pub fn id(&self) -> VersionId {
+        match self {
+            Version::Def(def) => def.id(),
+            Version::Need(def) => def.id(),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct VersionDef<'data> {
+    id: VersionId,
+    pub flags: u16,
+    pub names: Vec<&'data [u8]>,
+}
+
+impl<'data> VersionDef<'data> {
+    pub fn id(&self) -> VersionId {
+        self.id
+    }
+}
+
+#[derive(Debug)]
+pub struct VersionNeed<'data> {
+    id: VersionId,
+    pub flags: u16,
+    pub name: &'data [u8],
+    pub file: VersionFileId,
+}
+
+impl<'data> VersionNeed<'data> {
+    pub fn id(&self) -> VersionId {
+        self.id
+    }
+}
+
+#[derive(Debug)]
+pub struct Versions<'data>(Vec<Version<'data>>);
+
+impl<'data> Versions<'data> {
+    fn new() -> Self {
+        Versions(Vec::new())
+    }
+}
+
+impl<'a, 'data> IntoIterator for &'a Versions<'data> {
+    type Item = &'a Version<'data>;
+    type IntoIter = core::slice::Iter<'a, Version<'data>>;
+    fn into_iter(self) -> core::slice::Iter<'a, Version<'data>> {
+        self.0.as_slice().into_iter()
+    }
+}
+
+impl<'a, 'data> IntoIterator for &'a mut Versions<'data> {
+    type Item = &'a mut Version<'data>;
+    type IntoIter = core::slice::IterMut<'a, Version<'data>>;
+    fn into_iter(self) -> core::slice::IterMut<'a, Version<'data>> {
+        self.0.as_mut_slice().into_iter()
+    }
+}
+
+#[derive(Debug)]
+pub struct AttributesSection<'data> {
+    pub subsections: Vec<AttributesSubsection<'data>>,
+}
+
+impl<'data> AttributesSection<'data> {
+    pub fn new() -> Self {
+        AttributesSection {
+            subsections: Vec::new(),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct AttributesSubsection<'data> {
+    pub vendor: &'data [u8],
+    pub subsubsections: Vec<AttributesSubsubsection<'data>>,
+}
+
+impl<'data> AttributesSubsection<'data> {
+    pub fn new(vendor: &'data [u8]) -> Self {
+        AttributesSubsection {
+            vendor,
+            subsubsections: Vec::new(),
+        }
+    }
+}
+
+#[derive(Debug)]
+pub struct AttributesSubsubsection<'data> {
+    pub tag: AttributeTag,
+    pub data: &'data [u8],
+}
+
+#[derive(Debug)]
+pub enum AttributeTag {
+    File,
+    Section(Vec<SectionId>),
+    Symbol(Vec<SymbolId>),
+}
+
+impl AttributeTag {
+    pub fn tag(&self) -> u8 {
+        match self {
+            AttributeTag::File => elf::Tag_File,
+            AttributeTag::Section(_) => elf::Tag_Section,
+            AttributeTag::Symbol(_) => elf::Tag_Symbol,
+        }
+    }
+}
diff --git a/src/write/elf/mod.rs b/src/write/elf/mod.rs
index 3a4f3716..d3341a23 100644
--- a/src/write/elf/mod.rs
+++ b/src/write/elf/mod.rs
@@ -7,3 +7,6 @@ mod object;
 
 mod writer;
 pub use writer::*;
+
+mod builder;
+pub use builder::*;
diff --git a/src/write/elf/writer.rs b/src/write/elf/writer.rs
index 97509249..b2b4dfb2 100644
--- a/src/write/elf/writer.rs
+++ b/src/write/elf/writer.rs
@@ -991,15 +991,16 @@ impl<'a> Writer<'a> {
     ///
     /// This function does nothing if no dynamic strings or symbols were defined.
     /// This must be called after [`Self::add_dynamic_string`].
-    pub fn reserve_dynstr(&mut self) {
+    pub fn reserve_dynstr(&mut self) -> usize {
         debug_assert_eq!(self.dynstr_offset, 0);
         if !self.need_dynstr {
-            return;
+            return 0;
         }
         // Start with null string.
         self.dynstr_data = vec![0];
         self.dynstr.write(1, &mut self.dynstr_data);
         self.dynstr_offset = self.reserve(self.dynstr_data.len(), 1);
+        self.dynstr_offset
     }
 
     /// Write the dynamic string table.
@@ -1100,15 +1101,16 @@ impl<'a> Writer<'a> {
     ///
     /// This function does nothing if no dynamic symbols were reserved.
     /// This must be called after [`Self::reserve_dynamic_symbol_index`].
-    pub fn reserve_dynsym(&mut self) {
+    pub fn reserve_dynsym(&mut self) -> usize {
         debug_assert_eq!(self.dynsym_offset, 0);
         if self.dynsym_num == 0 {
-            return;
+            return 0;
         }
         self.dynsym_offset = self.reserve(
             self.dynsym_num as usize * self.symbol_size(),
             self.elf_align,
         );
+        self.dynsym_offset
     }
 
     /// Write the null dynamic symbol.
@@ -1219,13 +1221,14 @@ impl<'a> Writer<'a> {
     /// Reserve the range for the `.dynamic` section.
     ///
     /// This function does nothing if `dynamic_num` is zero.
-    pub fn reserve_dynamic(&mut self, dynamic_num: usize) {
+    pub fn reserve_dynamic(&mut self, dynamic_num: usize) -> usize {
         debug_assert_eq!(self.dynamic_offset, 0);
         if dynamic_num == 0 {
-            return;
+            return 0;
         }
         self.dynamic_num = dynamic_num;
         self.dynamic_offset = self.reserve(dynamic_num * self.dyn_size(), self.elf_align);
+        self.dynamic_offset
     }
 
     /// Write alignment padding bytes prior to the `.dynamic` section.
@@ -1314,11 +1317,12 @@ impl<'a> Writer<'a> {
     ///
     /// `symbol_count` is the number of symbols in the hash,
     /// not the total number of symbols.
-    pub fn reserve_hash(&mut self, bucket_count: u32, chain_count: u32) {
+    pub fn reserve_hash(&mut self, bucket_count: u32, chain_count: u32) -> usize {
         self.hash_size = mem::size_of::<elf::HashHeader<Endianness>>()
             + bucket_count as usize * 4
             + chain_count as usize * 4;
         self.hash_offset = self.reserve(self.hash_size, self.elf_align);
+        self.hash_offset
     }
 
     /// Write a SysV hash section.
@@ -1381,12 +1385,18 @@ impl<'a> Writer<'a> {
     ///
     /// `symbol_count` is the number of symbols in the hash,
     /// not the total number of symbols.
-    pub fn reserve_gnu_hash(&mut self, bloom_count: u32, bucket_count: u32, symbol_count: u32) {
+    pub fn reserve_gnu_hash(
+        &mut self,
+        bloom_count: u32,
+        bucket_count: u32,
+        symbol_count: u32,
+    ) -> usize {
         self.gnu_hash_size = mem::size_of::<elf::GnuHashHeader<Endianness>>()
             + bloom_count as usize * self.elf_align
             + bucket_count as usize * 4
             + symbol_count as usize * 4;
         self.gnu_hash_offset = self.reserve(self.gnu_hash_size, self.elf_align);
+        self.gnu_hash_offset
     }
 
     /// Write a GNU hash section.
@@ -1501,12 +1511,13 @@ impl<'a> Writer<'a> {
     /// Reserve the range for the `.gnu.version` section.
     ///
     /// This function does nothing if no dynamic symbols were reserved.
-    pub fn reserve_gnu_versym(&mut self) {
+    pub fn reserve_gnu_versym(&mut self) -> usize {
         debug_assert_eq!(self.gnu_versym_offset, 0);
         if self.dynsym_num == 0 {
-            return;
+            return 0;
         }
         self.gnu_versym_offset = self.reserve(self.dynsym_num as usize * 2, 2);
+        self.gnu_versym_offset
     }
 
     /// Write the null symbol version entry.
@@ -1556,16 +1567,17 @@ impl<'a> Writer<'a> {
     }
 
     /// Reserve the range for the `.gnu.version_d` section.
-    pub fn reserve_gnu_verdef(&mut self, verdef_count: usize, verdaux_count: usize) {
+    pub fn reserve_gnu_verdef(&mut self, verdef_count: usize, verdaux_count: usize) -> usize {
         debug_assert_eq!(self.gnu_verdef_offset, 0);
         if verdef_count == 0 {
-            return;
+            return 0;
         }
         self.gnu_verdef_size = verdef_count * mem::size_of::<elf::Verdef<Endianness>>()
             + verdaux_count * mem::size_of::<elf::Verdaux<Endianness>>();
         self.gnu_verdef_offset = self.reserve(self.gnu_verdef_size, self.elf_align);
         self.gnu_verdef_count = verdef_count as u16;
         self.gnu_verdef_remaining = self.gnu_verdef_count;
+        self.gnu_verdef_offset
     }
 
     /// Write alignment padding bytes prior to a `.gnu.version_d` section.
@@ -1651,16 +1663,17 @@ impl<'a> Writer<'a> {
     }
 
     /// Reserve the range for the `.gnu.version_r` section.
-    pub fn reserve_gnu_verneed(&mut self, verneed_count: usize, vernaux_count: usize) {
+    pub fn reserve_gnu_verneed(&mut self, verneed_count: usize, vernaux_count: usize) -> usize {
         debug_assert_eq!(self.gnu_verneed_offset, 0);
         if verneed_count == 0 {
-            return;
+            return 0;
         }
         self.gnu_verneed_size = verneed_count * mem::size_of::<elf::Verneed<Endianness>>()
             + vernaux_count * mem::size_of::<elf::Vernaux<Endianness>>();
         self.gnu_verneed_offset = self.reserve(self.gnu_verneed_size, self.elf_align);
         self.gnu_verneed_count = verneed_count as u16;
         self.gnu_verneed_remaining = self.gnu_verneed_count;
+        self.gnu_verneed_offset
     }
 
     /// Write alignment padding bytes prior to a `.gnu.version_r` section.
@@ -1793,11 +1806,16 @@ impl<'a> Writer<'a> {
         self.buffer.write_bytes(data);
     }
 
+    /// Return the file size for the given number of relocations.
+    pub fn relocations_size(&self, count: usize, is_rela: bool) -> usize {
+        count * self.rel_size(is_rela)
+    }
+
     /// Reserve a file range for the given number of relocations.
     ///
     /// Returns the offset of the range.
     pub fn reserve_relocations(&mut self, count: usize, is_rela: bool) -> usize {
-        self.reserve(count * self.rel_size(is_rela), self.elf_align)
+        self.reserve(self.relocations_size(count, is_rela), self.elf_align)
     }
 
     /// Write alignment padding bytes prior to a relocation section.