[libc-commits] [libc] [libc] Export standard C symbols in the public packages for MacOS instead of namespaced C++ symbols. (PR #136100)

[via libc-commits]

https://github.com/lntue created https://github.com/llvm/llvm-project/pull/136100

None

>From 10ea67ded8ff06f7a4d6d452c1f50a2c229d4347 Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue at google.com>
Date: Thu, 17 Apr 2025 15:31:27 +0800
Subject: [PATCH] [libc] Export standard C symbols in the public packages for
 MacOS instead of namespaced C++ symbols.

---
 libc/src/__support/common.h | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
index 42e8a79187fac..15209b76978af 100644
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -37,17 +37,27 @@
 
 #define LLVM_LIBC_ATTR(name) EXPAND_THEN_SECOND(LLVM_LIBC_FUNCTION_ATTR_##name)
 
-// MacOS needs to be excluded because it does not support aliasing.
-#if defined(LIBC_COPT_PUBLIC_PACKAGING) && (!defined(__APPLE__))
+// At the moment, [[gnu::alias()]] is not supported on MacOS, and it is needed
+// to cleanly export and alias the C++ symbol `LIBC_NAMESPACE::func` with the C
+// symbol `func`.  So for public packaging on MacOS, we will only export the C
+// symbol.  Moreover, a C symbol `func` in macOS is mangled as `_func`.
+#if defined(LIBC_COPT_PUBLIC_PACKAGING)
+#ifndef __APPLE__
 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
   LLVM_LIBC_ATTR(name)                                                         \
   LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name)                       \
       __##name##_impl__ __asm__(#name);                                        \
   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \
   type __##name##_impl__ arglist
-#else
+#else // __APPLE__
+#define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
+  LLVM_LIBC_ATTR(name)                                                         \
+  LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) name asm("_" #name);  \
+  type name arglist
+#endif // __APPLE__
+#else  // LIBC_COPT_PUBLIC_PACKAGING
 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist) type name arglist
-#endif
+#endif // LIBC_COPT_PUBLIC_PACKAGING
 
 // This extra layer of macro allows `name` to be a macro to rename a function.
 #define LLVM_LIBC_FUNCTION(type, name, arglist)                                \