build/elf: add Builder (gimli-rs#618)

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

Also add the `object-rewrite` crate which provides higher
level operations for modification. Use this to replace
the elfcopy example.

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",
 ]
@@ -100,6 +104,6 @@ unstable-all = ["all", "unstable"]
 rustc-dep-of-std = ['core', 'compiler_builtins', 'alloc', 'memchr/rustc-dep-of-std']
 
 [workspace]
-members = ["crates/examples"]
+members = ["crates/*"]
 default-members = [".", "crates/examples"]
 resolver = "2"

crates/examples/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2018"
 
 [dependencies]
 clap = "4.3.24"
-memmap2 = "0.7.1"
+memmap2 = "0.9.4"
 object = { path = "../..", default-features = false }
 
 [dev-dependencies]
@@ -28,10 +28,6 @@ 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"]