[libc] Disable hidden visibility for LIBC_NAMESPACE with GCC

[petrhosek]

GCC emits a warning when using the visibility attribute which needs to be diagnosed and addressed, but this change should unbreak the GCC build as a temporary workaround.

The issue is tracked as #98548.

[llvmbot]

@llvm/pr-subscribers-libc

Author: Petr Hosek (petrhosek)

Changes

GCC emits a warning when using the visibility attribute which needs to be diagnosed and addressed, but this change should unbreak the GCC build as a temporary workaround.

---

Full diff: https://github.com/llvm/llvm-project/pull/98549.diff

1 Files Affected:

• (modified) libc/src/__support/macros/config.h (+6)

diff --git a/libc/src/__support/macros/config.h b/libc/src/__support/macros/config.h
index 5c3ec634449f8..23436365cc544 100644
--- a/libc/src/__support/macros/config.h
+++ b/libc/src/__support/macros/config.h
@@ -28,6 +28,7 @@
 #define LIBC_HAS_FEATURE(f) 0
 #endif
 
+#ifndef __GNUC__
 // Declare a LIBC_NAMESPACE with hidden visibility. `namespace
 // LIBC_NAMESPACE_DECL {` should be used around all declarations and definitions
 // for libc internals as opposed to just `namespace LIBC_NAMESPACE {`. This
@@ -37,5 +38,10 @@
 // dynamic relocations. This does not affect the public C symbols which are
 // controlled independently via `LLVM_LIBC_FUNCTION_ATTR`.
 #define LIBC_NAMESPACE_DECL [[gnu::visibility("hidden")]] LIBC_NAMESPACE
+#else
+// TODO(#98548): GCC emits a warning when using the visibility attribute which
+// needs to be diagnosed and addressed.
+#define LIBC_NAMESPACE_DECL LIBC_NAMESPACE
+#endif
 
 #endif // LLVM_LIBC_SRC___SUPPORT_MACROS_CONFIG_H

[lntue]

I think clang also define this macro. Probably #ifdef __clang__ is safer?

[petrhosek]

Done.

[frobtech]

__GNUC__ is defined by many compilers, including Clang.
You need #ifdef __clang__ here.

[petrhosek]

Done.

[michaelrj-google]

doesn't clang define __GNUC__ for compatibility? Would it be better to instead use #ifdef __clang__ instead?

[petrhosek]

Done.

[jhuber6]

What is the warning? This should work in C++17 as far as I know https://godbolt.org/z/j94hxsTGa.

[michaelrj-google]

What is the warning? This should work in C++17 as far as I know https://godbolt.org/z/j94hxsTGa.

From the buildbot:

/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-gcc-fullbuild-dbg/llvm-project/libc/src/__support/big_int.h: In instantiation of ‘constexpr __llvm_libc_19_0_0_git::cpp::array<word, N> __llvm_libc_19_0_0_git::multiword::shift(__llvm_libc_19_0_0_git::cpp::array<word, N>, size_t) [with Direction direction = __llvm_libc_19_0_0_git::multiword::RIGHT; bool is_signed = false; word = long unsigned int; long unsigned int N = 5; size_t = long unsigned int]’:
/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-gcc-fullbuild-dbg/llvm-project/libc/src/__support/big_int.h:760:61:   required from ‘constexpr __llvm_libc_19_0_0_git::BigInt<Bits, Signed, WordType> __llvm_libc_19_0_0_git::BigInt<Bits, Signed, WordType>::operator>>(size_t) const [with long unsigned int Bits = 320; bool Signed = false; WordType = long unsigned int; size_t = long unsigned int]’
/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-gcc-fullbuild-dbg/llvm-project/libc/src/__support/float_to_string.h:390:29:   required from here
/home/llvm-libc-buildbot/buildbot-worker/libc-x86_64-debian-fullbuild/libc-x86_64-debian-gcc-fullbuild-dbg/llvm-project/libc/src/__support/big_int.h:281:28: error: ‘__llvm_libc_19_0_0_git::multiword::shift<__llvm_libc_19_0_0_git::multiword::RIGHT, false, long unsigned int, 5>(__llvm_libc_19_0_0_git::cpp::array<long unsigned int, 5>, size_t)::<lambda(size_t)>’ declared with greater visibility than the type of its field ‘__llvm_libc_19_0_0_git::multiword::shift<__llvm_libc_19_0_0_git::multiword::RIGHT, false, long unsigned int, 5>(__llvm_libc_19_0_0_git::cpp::array<long unsigned int, 5>, size_t)::<lambda(size_t)>::<array capture>’ [-Werror=attributes]
  281 |   const auto safe_get_at = [&](size_t index) -> word {
      |                            ^~~~~~~~~~~~~~~~~~~~~~~~~~~
  282 |     // return appropriate value when accessing out of bound elements.
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  283 |     const int i = at(index);
      |     ~~~~~~~~~~~~~~~~~~~~~~~~
  284 |     if (i < 0)
      |     ~~~~~~~~~~              
  285 |       return 0;
      |       ~~~~~~~~~             
  286 |     if (i >= int(N))
      |     ~~~~~~~~~~~~~~~~        
  287 |       return is_neg ? -1 : 0;
      |       ~~~~~~~~~~~~~~~~~~~~~~~
  288 |     return array[i];
      |     ~~~~~~~~~~~~~~~~        
  289 |   };
      |   ~