build/elf: add Builder

The Builder can be created from an existing ELF file, modified,
and then written out again.

Also replace the elfcopy example with a rewrite example that
uses Builder, and add some more options.

.github/workflows/rust.yml

@@ -39,8 +39,9 @@ jobs:
           submodules: true
       - run: cargo test --no-default-features --features read
       - run: cargo test --no-default-features --features write
+      - run: cargo test --no-default-features --features build
       - run: cargo test --no-default-features --features read_core,write_core,coff
-      - run: cargo test --no-default-features --features read_core,write_core,elf
+      - run: cargo test --no-default-features --features build_core,elf
       - run: cargo test --no-default-features --features read_core,write_core,macho
       - run: cargo test --no-default-features --features read_core,write_core,pe
       - run: cargo test --no-default-features --features read_core,wasm

Cargo.toml

@@ -41,6 +41,10 @@ write_core = ["dep:crc32fast", "dep:indexmap", "dep:hashbrown"]
 write_std = ["write_core", "std", "indexmap?/std", "crc32fast?/std"]
 # Write support for all file formats, including libstd features.
 write = ["write_std", "coff", "elf", "macho", "pe", "xcoff"]
+# Core builder support. You will need to enable some file formats too.
+build_core = ["read_core", "write_core"]
+# Builder support for all file formats.
+build = ["build_core", "write_std", "elf"]
 
 #=======================================
 # Misc features.
@@ -75,7 +79,7 @@ default = ["read", "compression"]
 #=======================================
 # Umbrella feature for enabling all user-facing features of this crate. Does not
 # enable internal features like `rustc-dep-of-std`.
-all = ["read", "write", "std", "compression", "wasm"]
+all = ["read", "write", "build", "std", "compression", "wasm"]
 
 # Use of --all-features is not supported.
 # This is a dummy feature to detect when --all-features is used.
@@ -84,7 +88,7 @@ cargo-all = []
 #=======================================
 # Documentation should be generated with everything in "all" except for "unaligned".
 doc = [
-  "read_core", "write_std",
+  "read_core", "write_std", "build_core",
   "std", "compression",
   "archive", "coff", "elf", "macho", "pe", "wasm", "xcoff",
 ]

crates/examples/Cargo.toml

@@ -4,6 +4,8 @@ version = "0.0.0"
 edition = "2018"
 
 [dependencies]
+anyhow = "1.0.79"
+bumpalo = "3.14.0"
 clap = "4.3.24"
 memmap2 = "0.7.1"
 object = { path = "../..", default-features = false }
@@ -14,9 +16,10 @@ glob = "0.3"
 [features]
 read = ["object/read"]
 write = ["object/write"]
+build = ["object/build"]
 wasm = ["object/wasm"]
 xcoff = ["object/xcoff"]
-all = ["read", "write", "wasm", "xcoff"]
+all = ["read", "write", "build", "wasm", "xcoff"]
 unstable-all = ["all"]
 default = ["read"]
 
@@ -28,10 +31,6 @@ required-features = ["object/read_core", "object/archive"]
 name = "dyldcachedump"
 required-features = ["object/read"]
 
-[[bin]]
-name = "elfcopy"
-required-features = ["object/read_core", "object/write_core", "object/elf", "object/std"]
-
 [[bin]]
 name = "elftoefi"
 required-features = ["object/read_core", "object/write_core", "object/elf", "object/pe", "object/std"]
@@ -59,3 +58,7 @@ required-features = ["object/read_core", "object/write_core", "object/pe", "obje
 [[bin]]
 name = "readobj"
 required-features = ["read"]
+
+[[bin]]
+name = "rewrite"
+required-features = ["build"]