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[OpenMP][AIX] Add pthreads and perfstat libraries for linking static libomp.a #167706

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[OpenMP][AIX] Add pthreads and perfstat libraries for linking static libomp.a #167706

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[OpenMP][AIX] Add pthreads and perfstat libraries for linking static …
kkwli Nov 12, 2025
6f8ea42
avoid duplication of -lpthreads in flang
kkwli Nov 13, 2025
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15 changes: 11 additions & 4 deletions clang/lib/Driver/ToolChains/AIX.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -297,6 +297,7 @@ void aix::Linker::ConstructJob(Compilation &C, const JobAction &JA,
}

// Add directory to library search path.
bool hasFOpenMP = false;
Args.AddAllArgs(CmdArgs, options::OPT_L);
if (!Args.hasArg(options::OPT_r)) {
ToolChain.AddFilePathLibArgs(Args, CmdArgs);
Expand All @@ -309,8 +310,9 @@ void aix::Linker::ConstructJob(Compilation &C, const JobAction &JA,
AddRunTimeLibs(ToolChain, D, CmdArgs, Args);

// Add OpenMP runtime if -fopenmp is specified.
if (Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
options::OPT_fno_openmp, false)) {
hasFOpenMP = Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
options::OPT_fno_openmp, false);
if (hasFOpenMP) {
switch (ToolChain.getDriver().getOpenMPRuntime(Args)) {
case Driver::OMPRT_OMP:
CmdArgs.push_back("-lomp");
Expand All @@ -325,10 +327,13 @@ void aix::Linker::ConstructJob(Compilation &C, const JobAction &JA,
// Already diagnosed.
break;
}

CmdArgs.push_back("-lperfstat");
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@DanielCChen DanielCChen Nov 12, 2025

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How to tell if this is only added for static libomp.a?

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@daltenty daltenty Nov 12, 2025

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Yeah, this is going to add it for the dynamic links as well, I don't know if that's a behaviour we want.

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@kkwli kkwli Nov 12, 2025

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@DanielCChen @daltenty
The situation is that libomp.a is a static library (i.e. ar t shows only .o) and we link it by default (i.e. -by option). It fails with missing pthread_* and ptx_* symbols. Adding the two libraries resolves the issues. Before and after the patch, ldd shows:

         /usr/lib/libpthreads.a(shr_xpg5_64.o)
         /usr/lib/libperfstat.a(shr_64.o)

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@DanielCChen DanielCChen Nov 12, 2025

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If I understand correctly, there is not doubt that we need this IF the libomp.a is built as a static library. I think the question is if libomp.a is built as a shared library, we probably don't want to link to -lperfstat, and this PR doesn't seem differentiate that.

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@kkwli kkwli Nov 12, 2025

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If the shared libomp.a is built (i.e. -DLIBOMP_ENABLE_SHARED=ON), it contains only libomp.so.1 as returned by at t. The shared library also has dependency on libperfstat.a.

$ dump -H ./runtimes/runtimes-bins/openmp/runtime/src/libomp.a

./runtimes/runtimes-bins/openmp/runtime/src/libomp.a[libomp.so.1]:

                        ***Loader Section***
...  
                        ***Import File Strings***
INDEX  PATH                          BASE                MEMBER              
0      /home/kli/wrk/f/build-flang/lib/clang/22/lib/powerpc64-ibm-aix:/usr/lib:/lib:                                         
1                                    libc.a              shr_64.o            
2                                    libpthreads.a       shr_xpg5_64.o       
3                                    libperfstat.a       shr_64.o

For linking this shared library (libomp.a), adding -lperfstat will not change the behavior as far as I know.

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@kkwli kkwli Nov 13, 2025

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For dynamic linking, there is no extra dependence based on the output of ldd.

Without -lperfstat,

$ /usr/bin/ld -o a.out -b64 -bpT:0x100000000 -bpD:0x110000000 /usr/lib/crt0_64.o /usr/lib/crti_64.o -bcdtors:all:0:s parallel.o -L/home/kli/llvm-install/bin/../lib/powerpc64-ibm-aix /home/kli/llvm-install/lib/clang/22/lib/powerpc64-ibm-aix/libclang_rt.builtins.a -lunwind -lomp -lc
$ ldd a.out
a.out needs:
         /usr/lib/libc.a(shr_64.o)
         /home/kli/llvm-install/bin/../lib/powerpc64-ibm-aix/libomp.a(libomp.so.1)
         /unix
         /usr/lib/libcrypt.a(shr_64.o)
         /usr/lib/libpthreads.a(shr_xpg5_64.o)
         /usr/lib/libperfstat.a(shr_64.o)
         /usr/lib/libcfg.a(shr_64.o)
         /usr/lib/libodm.a(shr_64.o)
         /usr/lib/liblvm.a(shr_64.o)
         /usr/lib/libcorcfg.a(shr_64.o)
         /usr/lib/libsrc.a(shr_64.o)

With -lperfstat,

$ /usr/bin/ld -o a.out -b64 -bpT:0x100000000 -bpD:0x110000000 /usr/lib/crt0_64.o /usr/lib/crti_64.o -bcdtors:all:0:s parallel.o -L/home/kli/llvm-install/bin/../lib/powerpc64-ibm-aix /home/kli/llvm-install/lib/clang/22/lib/powerpc64-ibm-aix/libclang_rt.builtins.a -lunwind -lomp -lc -lperfstat
$ ldd a.out
a.out needs:
         /usr/lib/libc.a(shr_64.o)
         /home/kli/llvm-install/bin/../lib/powerpc64-ibm-aix/libomp.a(libomp.so.1)
         /unix
         /usr/lib/libcrypt.a(shr_64.o)
         /usr/lib/libpthreads.a(shr_xpg5_64.o)
         /usr/lib/libperfstat.a(shr_64.o)
         /usr/lib/libcfg.a(shr_64.o)
         /usr/lib/libodm.a(shr_64.o)
         /usr/lib/liblvm.a(shr_64.o)
         /usr/lib/libcorcfg.a(shr_64.o)
         /usr/lib/libsrc.a(shr_64.o)

}

// Support POSIX threads if "-pthreads" or "-pthread" is present.
if (Args.hasArg(options::OPT_pthreads, options::OPT_pthread))
if (hasFOpenMP ||
Args.hasArg(options::OPT_pthreads, options::OPT_pthread))
CmdArgs.push_back("-lpthreads");

if (D.CCCIsCXX())
Expand All @@ -350,7 +355,9 @@ void aix::Linker::ConstructJob(Compilation &C, const JobAction &JA,
ToolChain.addFortranRuntimeLibraryPath(Args, CmdArgs);
ToolChain.addFortranRuntimeLibs(Args, CmdArgs);
CmdArgs.push_back("-lm");
CmdArgs.push_back("-lpthread");
// If the -fopenmp option is specified, no need to add it again.
if (!hasFOpenMP)
CmdArgs.push_back("-lpthreads");
}
const char *Exec = Args.MakeArgString(ToolChain.GetLinkerPath());
C.addCommand(std::make_unique<Command>(JA, *this, ResponseFileSupport::None(),
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