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Support rust metadata for AIX.
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@EsmeYi
EsmeYi committed May 23, 2023
1 parent 4400d8f commit 18fdca3
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Showing 2 changed files with 139 additions and 12 deletions.
2 changes: 1 addition & 1 deletion compiler/rustc_codegen_ssa/Cargo.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@ libc = "0.2.50"
[dependencies.object]
version = "0.31.1"
default-features = false
features = ["read_core", "elf", "macho", "pe", "unaligned", "archive", "write"]
features = ["read_core", "elf", "macho", "pe", "xcoff", "unaligned", "archive", "write"]

[target.'cfg(windows)'.dependencies.windows]
version = "0.48.0"
Expand Down
149 changes: 138 additions & 11 deletions compiler/rustc_codegen_ssa/src/back/metadata.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -6,8 +6,8 @@ use std::path::Path;

use object::write::{self, StandardSegment, Symbol, SymbolSection};
use object::{
elf, pe, Architecture, BinaryFormat, Endianness, FileFlags, Object, ObjectSection,
SectionFlags, SectionKind, SymbolFlags, SymbolKind, SymbolScope,
elf, pe, xcoff, Architecture, BinaryFormat, Endianness, FileFlags, Object, ObjectSection,
ObjectSymbol, SectionFlags, SectionKind, SymbolFlags, SymbolKind, SymbolScope,
};

use snap::write::FrameEncoder;
Expand Down Expand Up @@ -35,6 +35,8 @@ use rustc_target::spec::{RelocModel, Target};
#[derive(Debug)]
pub struct DefaultMetadataLoader;

static AIX_METADATA_SYMBOL_NAME: &'static str = "__aix_rust_metadata";

fn load_metadata_with(
path: &Path,
f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>,
Expand All @@ -48,7 +50,7 @@ fn load_metadata_with(
}

impl MetadataLoader for DefaultMetadataLoader {
fn get_rlib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
fn get_rlib_metadata(&self, target: &Target, path: &Path) -> Result<OwnedSlice, String> {
load_metadata_with(path, |data| {
let archive = object::read::archive::ArchiveFile::parse(&*data)
.map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?;
Expand All @@ -60,16 +62,24 @@ impl MetadataLoader for DefaultMetadataLoader {
let data = entry
.data(data)
.map_err(|e| format!("failed to parse rlib '{}': {}", path.display(), e))?;
return search_for_section(path, data, ".rmeta");
if target.is_like_aix {
return get_metadata_xcoff(path, data);
} else {
return search_for_section(path, data, ".rmeta");
}
}
}

Err(format!("metadata not found in rlib '{}'", path.display()))
})
}

fn get_dylib_metadata(&self, _target: &Target, path: &Path) -> Result<OwnedSlice, String> {
load_metadata_with(path, |data| search_for_section(path, data, ".rustc"))
fn get_dylib_metadata(&self, target: &Target, path: &Path) -> Result<OwnedSlice, String> {
if target.is_like_aix {
load_metadata_with(path, |data| get_metadata_xcoff(path, data))
} else {
load_metadata_with(path, |data| search_for_section(path, data, ".rustc"))
}
}
}

Expand Down Expand Up @@ -141,6 +151,33 @@ fn add_gnu_property_note(
file.append_section_data(section, &data, 8);
}

pub(super) fn get_metadata_xcoff<'a>(path: &Path, data: &'a [u8]) -> Result<&'a [u8], String> {
let Ok(file) = object::File::parse(data) else {
return Ok(data);
};
let info_data = search_for_section(path, data, ".info")?;
if let Some(metadata_symbol) =
file.symbols().find(|sym| sym.name() == Ok(AIX_METADATA_SYMBOL_NAME))
{
let offset = metadata_symbol.address() as usize;
if offset < 4 {
return Err(format!("Invalid metadata symbol offset: {}", offset));
}
// The offset specifies the location of rustc metadata in the comment section.
// The metadata is preceded by a 4-byte length field.
let len = u32::from_be_bytes(info_data[(offset - 4)..offset].try_into().unwrap()) as usize;
if offset + len > (info_data.len() as usize) {
return Err(format!(
"Metadata at offset {} with size {} is beyond .info section",
offset, len
));
}
return Ok(&info_data[offset..(offset + len)]);
} else {
return Err(format!("Unable to find symbol {}", AIX_METADATA_SYMBOL_NAME));
};
}

pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
let endianness = match sess.target.options.endian {
Endian::Little => Endianness::Little,
Expand Down Expand Up @@ -183,6 +220,8 @@ pub(crate) fn create_object_file(sess: &Session) -> Option<write::Object<'static
BinaryFormat::MachO
} else if sess.target.is_like_windows {
BinaryFormat::Coff
} else if sess.target.is_like_aix {
BinaryFormat::Xcoff
} else {
BinaryFormat::Elf
};
Expand Down Expand Up @@ -319,11 +358,15 @@ pub fn create_wrapper_file(
// to add a case above.
return (data.to_vec(), MetadataPosition::Last);
};
let section = file.add_section(
file.segment_name(StandardSegment::Debug).to_vec(),
section_name,
SectionKind::Debug,
);
let section = if file.format() == BinaryFormat::Xcoff {
file.add_section(Vec::new(), b".info".to_vec(), SectionKind::Debug)
} else {
file.add_section(
file.segment_name(StandardSegment::Debug).to_vec(),
section_name,
SectionKind::Debug,
)
};
match file.format() {
BinaryFormat::Coff => {
file.section_mut(section).flags =
Expand All @@ -333,6 +376,30 @@ pub fn create_wrapper_file(
file.section_mut(section).flags =
SectionFlags::Elf { sh_flags: elf::SHF_EXCLUDE as u64 };
}
BinaryFormat::Xcoff => {
file.add_section(Vec::new(), b".text".to_vec(), SectionKind::Text);
file.section_mut(section).flags =
SectionFlags::Xcoff { s_flags: xcoff::STYP_INFO as u32 };

let len = data.len() as u32;
let offset = file.append_section_data(section, &len.to_be_bytes(), 1);
// Add a symbol referring to the data in .info section.
file.add_symbol(Symbol {
name: AIX_METADATA_SYMBOL_NAME.into(),
value: offset + 4,
size: 0,
kind: SymbolKind::Unknown,
scope: SymbolScope::Dynamic,
weak: false,
section: SymbolSection::Section(section),
flags: SymbolFlags::Xcoff {
n_sclass: xcoff::C_INFO,
x_smtyp: xcoff::C_HIDEXT,
x_smclas: xcoff::C_HIDEXT,
containing_csect: None,
},
});
}
_ => {}
};
file.append_section_data(section, data, 1);
Expand Down Expand Up @@ -369,6 +436,9 @@ pub fn create_compressed_metadata_file(
let Some(mut file) = create_object_file(sess) else {
return compressed.to_vec();
};
if file.format() == BinaryFormat::Xcoff {
return create_compressed_metadata_file_for_xcoff(file, &compressed, symbol_name);
}
let section = file.add_section(
file.segment_name(StandardSegment::Data).to_vec(),
b".rustc".to_vec(),
Expand Down Expand Up @@ -398,3 +468,60 @@ pub fn create_compressed_metadata_file(

file.write().unwrap()
}

/// * Xcoff - On AIX, custom sections are merged into predefined sections,
/// so custom .rustc section is not preserved during linking.
/// For this reason, we store metadata in predefined .info section, and
/// define a symbol to reference the metadata. To preserve metadata during
/// linking on AIX, we have to
/// 1. Create an empty .text section, a empty .data section.
/// 2. Define an empty symbol named `symbol_name` inside .data section.
/// 3. Define an symbol named `AIX_METADATA_SYMBOL_NAME` referencing
/// data inside .info section.
/// From XCOFF's view, (2) creates a csect entry in the symbol table, the
/// symbol created by (3) is a info symbol for the preceding csect. Thus
/// two symbols are preserved during linking and we can use the second symbol
/// to reference the metadata.
pub fn create_compressed_metadata_file_for_xcoff(
mut file: write::Object<'_>,
data: &[u8],
symbol_name: &str,
) -> Vec<u8> {
assert!(file.format() == BinaryFormat::Xcoff);
file.add_section(Vec::new(), b".text".to_vec(), SectionKind::Text);
let data_section = file.add_section(Vec::new(), b".data".to_vec(), SectionKind::Data);
let section = file.add_section(Vec::new(), b".info".to_vec(), SectionKind::Debug);
file.add_file_symbol("lib.rmeta".into());
file.section_mut(section).flags = SectionFlags::Xcoff { s_flags: xcoff::STYP_INFO as u32 };
// Add a global symbol to data_section.
file.add_symbol(Symbol {
name: symbol_name.as_bytes().into(),
value: 0,
size: 0,
kind: SymbolKind::Data,
scope: SymbolScope::Dynamic,
weak: true,
section: SymbolSection::Section(data_section),
flags: SymbolFlags::None,
});
let len = data.len() as u32;
let offset = file.append_section_data(section, &len.to_be_bytes(), 1);
// Add a symbol referring to the rustc metadata.
file.add_symbol(Symbol {
name: AIX_METADATA_SYMBOL_NAME.into(),
value: offset + 4, // The metadata is preceded by a 4-byte length field.
size: 0,
kind: SymbolKind::Unknown,
scope: SymbolScope::Dynamic,
weak: false,
section: SymbolSection::Section(section),
flags: SymbolFlags::Xcoff {
n_sclass: xcoff::C_INFO,
x_smtyp: xcoff::C_HIDEXT,
x_smclas: xcoff::C_HIDEXT,
containing_csect: None,
},
});
file.append_section_data(section, data, 1);
file.write().unwrap()
}

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