release/21.x: opencl: Ensure printf symbol is not mangled. (#150210)

[llvmbot]

Backport a22d010

Requested by: @svenvh

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@svenvh What do you think about merging this PR to the release branch?

[llvmbot]

@llvm/pr-subscribers-backend-x86

@llvm/pr-subscribers-clang

Author: None (llvmbot)

Changes

Backport a22d010

Requested by: @svenvh

---

Full diff: https://github.com/llvm/llvm-project/pull/150960.diff

1 Files Affected:

• (modified) clang/lib/Headers/opencl-c-base.h (+10-1)

diff --git a/clang/lib/Headers/opencl-c-base.h b/clang/lib/Headers/opencl-c-base.h
index 2b7f5043e09e4..6206a347852be 100644
--- a/clang/lib/Headers/opencl-c-base.h
+++ b/clang/lib/Headers/opencl-c-base.h
@@ -697,7 +697,16 @@ template <typename _Tp> struct __remove_address_space<__constant _Tp> {
 #if defined(__OPENCL_CPP_VERSION__) || (__OPENCL_C_VERSION__ >= CL_VERSION_1_2)
 // OpenCL v1.2 s6.12.13, v2.0 s6.13.13 - printf
 
-int printf(__constant const char* st, ...) __attribute__((format(printf, 1, 2)));
+#ifdef __OPENCL_CPP_VERSION__
+#define CLINKAGE extern "C"
+#else
+#define CLINKAGE
+#endif
+
+CLINKAGE int printf(__constant const char *st, ...)
+    __attribute__((format(printf, 1, 2)));
+
+#undef CLINKAGE
 #endif
 
 #ifdef cl_intel_device_side_avc_motion_estimation

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@svenvh (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.