Release overlay GCC build fails with "aliased to external symbol"

[liam-clink]

CMake invocation: (C/C++ compilers set to GCC/G++)

cmake -S ../llvm -B . -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$HOME/llvm-15_temp -DLLVM_TARGETS_TO_BUILD="X86" -DLLVM_ENABLE_PROJECTS="all"

[1/7688] Building CXX object projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o
FAILED: projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o 
/home/liam/gcc-12.2.0/bin/g++ -D_GNU_SOURCE -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc/src/stdlib -I/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib -I/home/liam/Documents/GitHub/llvm-project/build/include -I/home/liam/Documents/GitHub/llvm-project/llvm/include -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc/include -I/home/liam/Documents/GitHub/llvm-project/libc -I/home/liam/Documents/GitHub/llvm-project/build/projects/libc -fPIC -fno-semantic-interposition -fvisibility-inlines-hidden -Werror=date-time -Wall -Wextra -Wno-unused-parameter -Wwrite-strings -Wcast-qual -Wno-missing-field-initializers -pedantic -Wno-long-long -Wimplicit-fallthrough -Wno-maybe-uninitialized -Wno-class-memaccess -Wno-redundant-move -Wno-pessimizing-move -Wno-noexcept-type -Wdelete-non-virtual-dtor -Wsuggest-override -Wno-comment -Wmisleading-indentation -fdiagnostics-color -ffunction-sections -fdata-sections -O3 -DNDEBUG -fpie -ffreestanding -fno-builtin -fno-exceptions -fno-unwind-tables -fno-asynchronous-unwind-tables -fno-rtti -DLLVM_LIBC_PUBLIC_PACKAGING -std=c++17 -MD -MT projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o -MF projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o.d -o projects/libc/src/stdlib/CMakeFiles/libc.src.stdlib.bsearch.dir/bsearch.cpp.o -c /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp
In file included from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:10:
/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:16:28: error: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' aliased to external symbol 'bsearch'
   16 | LLVM_LIBC_FUNCTION(void *, bsearch,
      |                            ^~~~~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/__support/common.h:33:31: note: in definition of macro 'LLVM_LIBC_FUNCTION'
   33 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:16:28: warning: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' specifies less restrictive attribute than its target 'void* bsearch(const void*, const void*, size_t, size_t, __compar_fn_t)': 'nonnull' [-Wmissing-attributes]
   16 | LLVM_LIBC_FUNCTION(void *, bsearch,
      |                            ^~~~~~~
/home/liam/Documents/GitHub/llvm-project/libc/src/__support/common.h:33:31: note: in definition of macro 'LLVM_LIBC_FUNCTION'
   33 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
In file included from /usr/include/stdlib.h:833,
                 from /home/liam/gcc-12.2.0/include/c++/12.2.0/cstdlib:75,
                 from /home/liam/gcc-12.2.0/include/c++/12.2.0/stdlib.h:36,
                 from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.h:9,
                 from /home/liam/Documents/GitHub/llvm-project/libc/src/stdlib/bsearch.cpp:9:
/usr/include/x86_64-linux-gnu/bits/stdlib-bsearch.h:20:1: note: 'void* __llvm_libc::bsearch(const void*, const void*, size_t, size_t, int (*)(const void*, const void*))' target declared here
   20 | bsearch (const void *__key, const void *__base, size_t __nmemb, size_t __size,
      | ^~~~~~~

[llvmbot]

@llvm/issue-subscribers-libc

[DavidSpickett]

Just been looking at this myself, this only happens for overlay mode. It's the overlaying mechanism that leads to this error I think.

Reading the gcc docs:
https://gcc.gnu.org/onlinedocs/gcc-4.7.2/gcc/Function-Attributes.html

"It is an error if `__f' is not defined in the same translation unit."

clang does not document it so I don't know if clang allows this on purpose or not.

I also found https://stackoverflow.com/questions/7649979/gcc-alias-to-function-outside-of-translation-unit-aka-is-this-even-the-right-t asking about this with another project. No obvious solution from C, but some ideas with linker scripts and such.

I should note that the libc project only officially supports clang at this time. The gcc buildbots they have build the full mode so they won't have hit this.

[sivachandra]

Interestingly, this seems to happen only for release mode builds with -DCMAKE_BUILD_TYPE=Release. I am not able to reproduce this for debug builds.

[sivachandra]

Ah, looks like bsearch gets defined as an extern inline function in glibc's stdlib.h under release build and so the alias here is conflicting with that extern inline function.

[mikhailramalho]

I also started to get the same error for readlinkat in RelWithDebInfo mode:

In file included from /home/mgadelha/tools/llvm-project/libc/src/__support/OSUtil/linux/syscall.h:12,
                 from /home/mgadelha/tools/llvm-project/libc/src/__support/OSUtil/syscall.h:13,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:11:
/home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:20:29: error: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ aliased to external symbol ‘readlinkat’
   20 | LLVM_LIBC_FUNCTION(ssize_t, readlinkat,
      |                             ^~~~~~~~~~
/home/mgadelha/tools/llvm-project/libc/src/__support/common.h:30:31: note: in definition of macro ‘LLVM_LIBC_FUNCTION’
   30 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
/home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:20:29: warning: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ specifies less restrictive attributes than its target ‘ssize_t readlinkat(int, const char*, char*, size_t)’: ‘leaf’, ‘nonnull’, ‘nothrow’ [-Wmissing-attributes]
   20 | LLVM_LIBC_FUNCTION(ssize_t, readlinkat,
      |                             ^~~~~~~~~~
/home/mgadelha/tools/llvm-project/libc/src/__support/common.h:30:31: note: in definition of macro ‘LLVM_LIBC_FUNCTION’
   30 |   decltype(__llvm_libc::name) name [[gnu::alias(#name)]];                      \
      |                               ^~~~
In file included from /usr/include/features.h:486,
                 from /usr/include/unistd.h:25,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/readlinkat.h:12,
                 from /home/mgadelha/tools/llvm-project/libc/src/unistd/linux/readlinkat.cpp:9:
/usr/include/x86_64-linux-gnu/bits/unistd.h:144:1: note: ‘ssize_t __llvm_libc::readlinkat(int, const char*, char*, size_t)’ target declared here
  144 | __NTH (readlinkat (int __fd, const char *__restrict __path,
      | ^~~~~

It builds fine in Debug mode.

[erkinalp]

Suggested re-title: "Standard library re-aliasing issues in overlay mode builds only in the release configuration"