[powerpc64le][XRay] XRay fails with linker errors when building C codes

[Thyre]

This initially came up after merging #140068. Build Bots for powerpc64le started failing because of an added C test, with the following error message:

AIL: XRay-powerpc64le-linux :: TestCases/Posix/patching-unpatching.c (4110 of 4158)
******************** TEST 'XRay-powerpc64le-linux :: TestCases/Posix/patching-unpatching.c' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/users/reuter1/Sources/llvm-project/_build/./bin/clang  -fxray-instrument  -m64 -fno-function-sections  -fxray-instrument -std=c23 /storage/users/reuter1/Sources/llvm-project/compiler-rt/test/xray/TestCases/Posix/patching-unpatching.c -o /storage/users/reuter1/Sources/llvm-project/_build/runtimes/runtimes-bins/compiler-rt/test/xray/POWERPC64LELinuxConfig/TestCases/Posix/Output/patching-unpatching.c.tmp # RUN: at line 4
+ /home/users/reuter1/Sources/llvm-project/_build/./bin/clang -fxray-instrument -m64 -fno-function-sections -fxray-instrument -std=c23 /storage/users/reuter1/Sources/llvm-project/compiler-rt/test/xray/TestCases/Posix/patching-unpatching.c -o /storage/users/reuter1/Sources/llvm-project/_build/runtimes/runtimes-bins/compiler-rt/test/xray/POWERPC64LELinuxConfig/TestCases/Posix/Output/patching-unpatching.c.tmp
/storage/users/reuter1/Sources/llvm-project/_build/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-basic.a(xray_basic_logging.cpp.o): In function `__xray::basicLoggingInit(unsigned long, unsigned long, void*, unsigned long)::$_0::__invoke()':
/usr/include/sys/platform/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/_build/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-basic.a(xray_basic_logging.cpp.o): In function `__xray::getLog()::$_0::__invoke()':
/usr/include/sys/platform/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/_build/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-fdr.a(xray_fdr_logging.cpp.o): In function `__xray::fdrCommonHeaderInfo()::$_0::__invoke()':
/usr/lib/gcc/ppc64le-redhat-linux/8/../../../../include/c++/8/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/_build/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-fdr.a(xray_fdr_logging.cpp.o): In function `__xray::fdrLoggingInit(unsigned long, unsigned long, void*, unsigned long)::$_0::__invoke()':
/usr/lib/gcc/ppc64le-redhat-linux/8/../../../../include/c++/8/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I was able to reproduce the message shown above on a Power10 machine. Build failures can be seen at:

• https://lab.llvm.org/buildbot/#/builders/95/builds/13758
• https://lab.llvm.org/buildbot/#/builders/72/builds/11568
• https://lab.llvm.org/buildbot/#/builders/76/builds/9949

Looking into this a bit further, the issue is not limited to the linked PR, nor the compiler-rt XRay tests.
See the following reproducer:

[reuter1@mammatus _build]$ which clang
~/Sources/llvm-project/stage1.install/bin/clang
[reuter1@mammatus _build]$ clang --version
clang version 21.0.0git (https://github.com/llvm/llvm-project.git 1d5bf04030f0345690243553a7d2ea8f60b26604)
Target: powerpc64le-unknown-linux-gnu
Thread model: posix
InstalledDir: /storage/users/reuter1/Sources/llvm-project/stage1.install/bin
Build config: +assertions
[reuter1@mammatus _build]$ cat test.c
int main( void )
{}
[reuter1@mammatus _build]$ clang -fxray-instrument -fxray-instruction-threshold=1 test.c 
/storage/users/reuter1/Sources/llvm-project/stage1.install/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-basic.a(xray_basic_logging.cpp.o): In function `__xray::basicLoggingInit(unsigned long, unsigned long, void*, unsigned long)::$_0::__invoke()':
/usr/include/sys/platform/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/stage1.install/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-basic.a(xray_basic_logging.cpp.o): In function `__xray::getLog()::$_0::__invoke()':
/usr/include/sys/platform/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/stage1.install/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-fdr.a(xray_fdr_logging.cpp.o): In function `__xray::fdrCommonHeaderInfo()::$_0::__invoke()':
/usr/lib/gcc/ppc64le-redhat-linux/8/../../../../include/c++/8/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
/storage/users/reuter1/Sources/llvm-project/stage1.install/lib/clang/21/lib/powerpc64le-unknown-linux-gnu/libclang_rt.xray-fdr.a(xray_fdr_logging.cpp.o): In function `__xray::fdrLoggingInit(unsigned long, unsigned long, void*, unsigned long)::$_0::__invoke()':
/usr/lib/gcc/ppc64le-redhat-linux/8/../../../../include/c++/8/gthr-default.h:107: undefined reference to `std::__throw_system_error(int)'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

This commit is just before the PR changes landed. Trying to build a C code with XRay enabled causes the same linker errors to appear. LLVM is built with the pretty much the same arguments used for one of the build runner builds:

$ cmake ../llvm -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=True '-DLLVM_LIT_ARGS='"'"'-v'"'"'' -DCMAKE_INSTALL_PREFIX=../stage1.install -DLLVM_ENABLE_ASSERTIONS=ON -DBUILD_SHARED_LIBS=ON -DCMAKE_C_COMPILER_LAUNCHER=gcc -DCMAKE_CXX_COMPILER_LAUNCHER=g++ '-DLLVM_ENABLE_PROJECTS=clang-tools-extra;clang;llvm' -DLLVM_ENABLE_RUNTIMES=compiler-rt

This may also affect Fortran, but I unfortunately haven't built flang in addition to clang.

CC: @sebastiankreutzer

[Thyre]

Some more pointers:

• Building without -DBUILD_SHARED_LIBS=ON doesn't change anything
• Linking with -lstdc++ works, but is probably not intended for C code
• The linked function actually shows up in objdump

  pthread_once(&OnceInit, +[] {
     eec:       90 00 21 38     addi    r1,r1,144
     ef0:       10 00 01 e8     ld      r0,16(r1)
     ef4:       f0 ff c1 eb     ld      r30,-16(r1)
     ef8:       e8 ff a1 eb     ld      r29,-24(r1)
     efc:       e0 ff 81 eb     ld      r28,-32(r1)
     f00:       d8 ff 61 eb     ld      r27,-40(r1)
     f04:       a6 03 08 7c     mtlr    r0
     f08:       20 00 80 4e     blr
     f0c:       01 00 00 48     bl      f0c <_ZZN6__xray16basicLoggingInitEmmPvmEN3$_08__invokeEv+0xfc>
                        f0c: R_PPC64_REL24      _ZSt20__throw_system_errori
     f10:       00 00 00 60     nop