[compiler-rt] [sanitizer_common] mark __elf_aux_vector as weak on FreeBSD (PR #118110)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: Dimitry Andric (DimitryAndric)

<details>
<summary>Changes</summary>

At some point FreeBSD introduced libsys as a wrapper between syscalls and libc, and then linking sanitized programs started failing with:

```text
  # c++ -fsanitize=address main.cc
  ld: error: undefined symbol: __elf_aux_vector
  >>> referenced by sanitizer_linux_libcdep.cpp:950 (/usr/src/contrib/llvm-project/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp:950)
  >>>               sanitizer_linux_libcdep.o:(__sanitizer::ReExec()) in archive /usr/lib/clang/17/lib/freebsd/libclang_rt.asan-x86_64.a
  c++: error: linker command failed with exit code 1 (use -v to see invocation)
```

Mark `__elf_aux_vector` as weak in the internal sanitizer declaration, so the linker will accept it at link time. The dynamic linker will then take care of the symbol at run time.


---
Full diff: https://github.com/llvm/llvm-project/pull/118110.diff


1 Files Affected:

- (modified) compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp (+1-1) 


``````````diff
diff --git a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
index 525bc1038619d8..700aa1c03d05e9 100644
--- a/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
+++ b/compiler-rt/lib/sanitizer_common/sanitizer_linux_libcdep.cpp
@@ -57,7 +57,7 @@
 // that, it was never implemented. So just define it to zero.
 #    undef MAP_NORESERVE
 #    define MAP_NORESERVE 0
-extern const Elf_Auxinfo *__elf_aux_vector;
+extern const Elf_Auxinfo *__elf_aux_vector __attribute__ ((weak));
 extern "C" int __sys_sigaction(int signum, const struct sigaction *act,
                                struct sigaction *oldact);
 #  endif

``````````

</details>


https://github.com/llvm/llvm-project/pull/118110