[Clang] Only link C device libraries by default for OpenMP

[jhuber6]

Summary:
We link these implicitly for OpenMP because it's the canonical
implementation of those C language features. This was inhereted by HIP
and ended up with these resolving functions. There are some useful
functions in here, but this can be problematic as it could potentially
override functions intended to be provided by the ROCm device libraries.
Additionally the HIP runtime does not currently provide the handling for
the RPC server required to run the host resources so those just segfault.

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Joseph Huber (jhuber6)

Changes

Summary:
We link these implicitly for OpenMP because it's the canonical
implementation of those C language features. This was inhereted by HIP
and ended up with these resolving functions. There are some useful
functions in here, but this can be problematic as it could potentially
override functions intended to be provided by the ROCm device libraries.
Additionally the HIP runtime does not currently provide the handling for
the RPC server required to run the host resources so those just segfault.

---

Full diff: https://github.com/llvm/llvm-project/pull/151239.diff

1 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Clang.cpp (+3-2)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 9d882dbfd0c65..6e1d4aa8bc053 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -9232,8 +9232,9 @@ void LinkerWrapper::ConstructJob(Compilation &C, const JobAction &JA,
                    options::OPT_nogpulibc)) {
     forAllAssociatedToolChains(C, JA, getToolChain(), [&](const ToolChain &TC) {
       // The device C library is only available for NVPTX and AMDGPU targets
-      // currently.
-      if (!TC.getTriple().isNVPTX() && !TC.getTriple().isAMDGPU())
+      // and we only link it by default for OpenMP currently.
+      if (!TC.getTriple().isNVPTX() && !TC.getTriple().isAMDGPU() ||
+          !JA.isHostOffloading(Action::OFK_OpenMP))
         return;
       bool HasLibC = TC.getStdlibIncludePath().has_value();
       if (HasLibC) {

[arsenm]

as it could potentially override functions intended to be provided by the ROCm device libraries.

These don't provide any of the standard entry point names

[arsenm]

Missing test

[jhuber6]

Missing test

I can't think of an easy way to test this since it looks at the compiler build tree.

[jhuber6]

as it could potentially override functions intended to be provided by the ROCm device libraries.

These don't provide any of the standard entry point names

It does in practice, though I haven't bothered to investigate why.

[arsenm]

Missing test

I can't think of an easy way to test this since it looks at the compiler build tree.

Not sure how this could depend on the build tree, but we have various tests targeting fake sysroots in clang/test/Driver/Inputs