build/elf: add Builder

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

Also change the elfcopy example to use 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"]
 
@@ -30,7 +33,7 @@ required-features = ["object/read"]
 
 [[bin]]
 name = "elfcopy"
-required-features = ["object/read_core", "object/write_core", "object/elf", "object/std"]
+required-features = ["build"]
 
 [[bin]]
 name = "elftoefi"