+whole-archive link modifier not behaving as expected on macOS

[ArthurKValladares]

I'm trying to link a C static lib to a rust cdylib using the +whole-archive link modifier in order to expose the library symbols from the generated dylib, but they do not show up in the final library. A minimal example is as follows:

static.c

#include <stdio.h>

void linking_c_static()
{
    printf("foo");
}

compiled using:

gcc -c -fPIC static.c -o static.o
ar -rv libstatic.a static.o

lib.rs

#[no_mangle]
pub fn rust_linking() {
    println!("hello!");
}

build.rs

fn main() {
    println!("cargo:rustc-link-lib=static:+whole-archive=static");
}

Cargo..toml

[package]
name = "rust"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib"]

I expected to see this happen:

I expected to be able to see the static lib symbols in the dylib, as I can when linking the same lib to a C dylib generated by gcc:
dynamic.c

#include <stdio.h>

void linking_c_dynamic()
{
    printf("bar");
}

compiled using:

gcc -c -fPIC dynamic.c -o dynamic.o
gcc -dynamiclib -o libdynamic.dylib dynamic.o -Wl,-force_load libstatic.a

Symbols listed nm -g libdynamic.dylib:

0000000000003f70 T _linking_c_dynamic
0000000000003f90 T _linking_c_static
                 U _printf

Instead, this happened:

Instead, I cannot find the static lib symbols in the generated dylib nm -g target/debug/librust.dylib:

                 U __Unwind_Backtrace
                 U __Unwind_GetDataRelBase
                 U __Unwind_GetIP
                 U __Unwind_GetIPInfo
                 U __Unwind_GetLanguageSpecificData
                 U __Unwind_GetRegionStart
                 U __Unwind_GetTextRelBase
                 U __Unwind_RaiseException
                 U __Unwind_Resume
                 U __Unwind_SetGR
                 U __Unwind_SetIP
                 U ___bzero
                 U ___error
                 U __dyld_get_image_header
                 U __dyld_get_image_name
                 U __dyld_get_image_vmaddr_slide
                 U __dyld_image_count
                 U __tlv_atexit
                 U __tlv_bootstrap
                 U _abort
                 U _close$NOCANCEL
                 U _closedir
                 U _dispatch_release
                 U _dispatch_semaphore_create
                 U _dispatch_semaphore_signal
                 U _dispatch_semaphore_wait
                 U _free
                 U _fstat$INODE64
                 U _getcwd
                 U _getenv
                 U _malloc
                 U _memcmp
                 U _memcpy
                 U _memmove
                 U _mmap
                 U _munmap
                 U _open
                 U _opendir$INODE64
                 U _posix_memalign
                 U _pthread_mutex_destroy
                 U _pthread_mutex_init
                 U _pthread_mutex_lock
                 U _pthread_mutex_trylock
                 U _pthread_mutex_unlock
                 U _pthread_mutexattr_destroy
                 U _pthread_mutexattr_init
                 U _pthread_mutexattr_settype
                 U _pthread_rwlock_destroy
                 U _pthread_rwlock_rdlock
                 U _pthread_rwlock_unlock
                 U _readdir_r$INODE64
                 U _realloc
0000000000003c20 T _rust_linking
                 U _strerror_r
                 U _strlen
                 U _write
                 U _writev

Meta

rustc --version --verbose:

rustc 1.68.2 (9eb3afe9e 2023-03-27)
binary: rustc
commit-hash: 9eb3afe9ebe9c7d2b84b71002d44f4a0edac95e0
commit-date: 2023-03-27
host: x86_64-apple-darwin
release: 1.68.2
LLVM version: 15.0.6

Backtrace

<backtrace>

Linker info:

arthurvalladares@Arthurs-MacBook rust % export RUSTC_LOG=rustc_codegen_ssa::back::link=info
arthurvalladares@Arthurs-MacBook rust % cargo build -v
   Compiling rust v0.1.0 (/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust)
     Running `rustc --crate-name build_script_build --edition=2021 build.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=80 --crate-type bin --emit=dep-info,link -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C metadata=9fc2614f827c81ce -C extra-filename=-9fc2614f827c81ce --out-dir /Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce -C incremental=/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/incremental -L dependency=/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps -C link-arg=-undefined -C link-arg=dynamic_lookup`
INFO rustc_codegen_ssa::back::link preparing Executable to "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce"
INFO rustc_codegen_ssa::back::link LC_ALL="C" PATH="/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/bin:/Users/arthurvalladares/.rvm/gems/ruby-2.7.2/bin:/Users/arthurvalladares/.rvm/gems/ruby-2.7.2@global/bin:/Users/arthurvalladares/.rvm/rubies/ruby-2.7.2/bin:/usr/local/opt/openssl@1.1/bin:/Users/arthurvalladares/Library/Android/sdk/platform-tools:/Users/arthurvalladares/Library/Android/sdk/tools:/Users/arthurvalladares/Documents/spirv-tools/bin:/Users/arthurvalladares/.pyenv/shims:/Library/Frameworks/Python.framework/Versions/3.8/bin:/Library/Frameworks/Python.framework/Versions/2.7/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin:/Users/arthurvalladares/.cargo/bin:/Users/arthurvalladares/.rvm/bin" VSLANG="1033" ZERO_AR_DATE="1" "cc" "-arch" "x86_64" "-m64" "/var/folders/g4/8gyynk8n1hl9frp6w3v22z4c0000gn/T/rustcYiGEDC/symbols.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.148w6spp8bbexu3h.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.18cdj71jewiji4xx.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.1k618e00qfe1nsxt.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.1n7ouiwlqty0qm0u.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.1t0yal8w4nqc9bey.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.1tba9wer1o6narf6.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.1xo7ohzz3fon8sgo.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.2dswrc8j2ez1uwpm.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.38vzlr9legqx14jg.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.3fn06lljzrbqhvqf.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.3k3szf92za1ihy5q.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.3m6csywzzqs15f0k.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.3rragy3p0g864p55.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.4lse6n2sxzesbdtj.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.4zruildvtdm7mk72.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.91fzws68jx5u5sq.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.b8e33l75m8j507m.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.ik1wraweljwlofa.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.nehcvldcc05ibxa.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.vay3url2ofecrpo.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.xcasarpz3rj3qfb.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce.58a7w3ajspfsi75.rcgu.o" "-L" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps" "-L" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libstd-8fa007cdc882403b.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libpanic_unwind-8294ffb4a69497ab.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libobject-472e943b681632d8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libmemchr-7d8d567e92ad1dd8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libaddr2line-ed004df1bb903adb.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libgimli-af580b13d5715ba8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_demangle-20fb3dd872494ad9.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libstd_detect-50a89c754eac916d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libhashbrown-9ac74abb1b852e5d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libminiz_oxide-68f98cc52d315b53.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libadler-35546c54bc82a9ad.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_alloc-bd9ee649e3151af7.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libunwind-235725c3b2d78362.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcfg_if-c569d380514bde32.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liblibc-20fad06cc491dc7d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liballoc-d6ca0a93cb563c8b.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_core-6f5d01ccd9a8d6da.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcore-1eef3d4aa79d6846.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcompiler_builtins-81f9fecd362517eb.rlib" "-lSystem" "-lc" "-lm" "-L" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "-o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build_script_build-9fc2614f827c81ce" "-Wl,-dead_strip" "-nodefaultlibs" "-undefined" "dynamic_lookup"
INFO rustc_codegen_ssa::back::link linker stderr:

INFO rustc_codegen_ssa::back::link linker stdout:

     Running `/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/build/rust-9fc2614f827c81ce/build-script-build`
     Running `rustc --crate-name rust --edition=2021 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=80 --crate-type cdylib --emit=dep-info,link -C embed-bitcode=no -C split-debuginfo=unpacked -C debuginfo=2 -C metadata=aadcbc7450cb9cc6 --out-dir /Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps -C incremental=/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/incremental -L dependency=/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps -C link-arg=-undefined -C link-arg=dynamic_lookup -L native=/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/../c -l 'static:+whole-archive=static'`
INFO rustc_codegen_ssa::back::link preparing Cdylib to "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps/librust.dylib"
INFO rustc_codegen_ssa::back::link LC_ALL="C" PATH="/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/bin:/Users/arthurvalladares/.rvm/gems/ruby-2.7.2/bin:/Users/arthurvalladares/.rvm/gems/ruby-2.7.2@global/bin:/Users/arthurvalladares/.rvm/rubies/ruby-2.7.2/bin:/usr/local/opt/openssl@1.1/bin:/Users/arthurvalladares/Library/Android/sdk/platform-tools:/Users/arthurvalladares/Library/Android/sdk/tools:/Users/arthurvalladares/Documents/spirv-tools/bin:/Users/arthurvalladares/.pyenv/shims:/Library/Frameworks/Python.framework/Versions/3.8/bin:/Library/Frameworks/Python.framework/Versions/2.7/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Library/Apple/usr/bin:/Users/arthurvalladares/.cargo/bin:/Users/arthurvalladares/.rvm/bin" VSLANG="1033" ZERO_AR_DATE="1" "cc" "-Wl,-exported_symbols_list,/var/folders/g4/8gyynk8n1hl9frp6w3v22z4c0000gn/T/rustcDEuymC/list" "-arch" "x86_64" "-m64" "/var/folders/g4/8gyynk8n1hl9frp6w3v22z4c0000gn/T/rustcDEuymC/symbols.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps/rust.2iirdhpfrzg7c1ux.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps/rust.3t24jnsy45ne6yne.rcgu.o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps/rust.27m1axkv3p075yww.rcgu.o" "-L" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps" "-L" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/../c" "-L" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "-Wl,-force_load" "-Wl,/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/../c/libstatic.a" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libstd-8fa007cdc882403b.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libpanic_unwind-8294ffb4a69497ab.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libobject-472e943b681632d8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libmemchr-7d8d567e92ad1dd8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libaddr2line-ed004df1bb903adb.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libgimli-af580b13d5715ba8.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_demangle-20fb3dd872494ad9.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libstd_detect-50a89c754eac916d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libhashbrown-9ac74abb1b852e5d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libminiz_oxide-68f98cc52d315b53.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libadler-35546c54bc82a9ad.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_alloc-bd9ee649e3151af7.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libunwind-235725c3b2d78362.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcfg_if-c569d380514bde32.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liblibc-20fad06cc491dc7d.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/liballoc-d6ca0a93cb563c8b.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/librustc_std_workspace_core-6f5d01ccd9a8d6da.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcore-1eef3d4aa79d6846.rlib" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib/libcompiler_builtins-81f9fecd362517eb.rlib" "-lSystem" "-lc" "-lm" "-L" "/Users/arthurvalladares/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/x86_64-apple-darwin/lib" "-o" "/Users/arthurvalladares/Documents/Brainium/rust-linking-test/rust/target/debug/deps/librust.dylib" "-Wl,-dead_strip" "-dynamiclib" "-Wl,-dylib" "-nodefaultlibs" "-undefined" "dynamic_lookup"
INFO rustc_codegen_ssa::back::link linker stderr:
ld: warning: -undefined dynamic_lookup may not work with chained fixups

INFO rustc_codegen_ssa::back::link linker stdout:

[Jules-Bertholet]

@rustbot label +A-linkage

[m00nwtchr]

I think I'm seeing the same thing on Linux.

rustc 1.69.0 (84c898d65 2023-04-16)
binary: rustc
commit-hash: 84c898d65adf2f39a5a98507f1fe0ce10a2b8dbc
commit-date: 2023-04-16
host: x86_64-unknown-linux-gnu
release: 1.69.0
LLVM version: 15.0.7

Strangely enough, I can get the symbol to show up if I add a extern "C" definition with #[no_mangle]

#[link(name = "p", kind = "static", modifiers = "+whole-archive")]
extern "C" {
	#[no_mangle]
	pub fn add(a: u32, b: u32) -> u32;
}

[petrochenkov]

I didn't check what happens in the examples in detail, but it's possible that linker throws away individual symbols due to --gc-sections, even if their object files are not thrown away due to +whole-archive.

Some attributes like #[no_mangle] can mark the symbol as exported, so it won't be garbage collected in that case.

[ArthurKValladares]

The extern "C" + #[no-mangle] combination @m00nwtchr described above does work for me as well. We do get a warning that this will become an error in the future:

warning: `#[no_mangle]` has no effect on a foreign function
 --> src/lib.rs:3:5
  |
3 |     #[no_mangle]
  |     ^^^^^^^^^^^^ help: remove this attribute
4 |     pub fn linking_c_static();
  |     -------------------------- foreign function
  |
  = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
  = note: symbol names in extern blocks are not mangled
  = note: `#[warn(unused_attributes)]` on by default

[aidanhs]

I think I'm seeing this on linux - it appears to be because the linker version script looks like:

{
  global:
    cxxbridge1$Recorder$init;
[...]

  local:
    *;
};

If I save my linker invocation and temporaries with cargo rustc --release -p rec-cxx -- -C save-temps --print link-args >out, edit the version script to remove the local section and then run sh out then I get the symbols included.

[bjorn3]

Are you using #[link(name = "...", kind = "static")] on the extern block that imports all functions you need? This is necessary for rustc to re-export them from a dylib.

[aidanhs]

I think what's described in this issue is that we want +whole-archive to pull an entire archive into a cdylib to re-export it without explicitly listing all the symbols from said archive (e.g. because the list changes often).

i.e.

• libext.a exports foo()
• crate
  • exports bar()
  • links to libext.a with +whole-archive without listing any symbols
• libcrate.so - exports foo and bar

In the OP that's being done via a build script whereas I have the annotations on an empty extern block, but we're trying to do the same thing.

#[link(name="recorder-cxx-bridge", kind="static", modifiers = "+whole-archive")]
extern "C" {}

If rustc won't support this, I think I have two options:

1. build a rust staticlib that I combine with my external staticlib into a cdylib by invoking the linker myself. That includes tons of symbols because of Don't leak non-exported symbols from staticlibs #104707, so I get rustc to emit the list of exported symbols (by parsing a version script saved with save-temps?), then use that list to generate my own version script which includes symbols from the ext library

2. use a build script to pull symbols from the external library and list them in the extern block at compile time

[aidanhs]

Ah but of course, with option 2 I'm hitting the warning in #110624 (comment) because I have to put no_mangle on the extern symbols to export them and rust wants to prevent that at some point. I guess it'll do for now.

Demo repo https://github.com/aidanhs/rust-re-export-lib/

Semi related #73958 which talks about no_mangle visibility.

[bjorn3]

#[no_mangle] inside an extern block shouldn't have any effect AFAIK. The kind = "static" inside #[link] should be enough for exporting all symbols defined in that block.

[aidanhs]

Unfortunately the repo above seems to demonstrate otherwise? At least on Linux (which matches up with what the other people in this issue have found).

[apiraino]

The --whole-archive hack was removed in Rust 1.82 (see changelog). Makes sense to close this issue or do we prefer it open to track the progress of RFC#3556?