[libc-commits] [libc] [libc] Allow each function can have extra attributes by defining LLVM_LIBC_FUNCTION_ATTR_func macro. (PR #116160)

[via libc-commits]

https://github.com/lntue updated https://github.com/llvm/llvm-project/pull/116160

>From 44637f4624e7c49055e5f417830cc0eb57b24e28 Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue at google.com>
Date: Wed, 13 Nov 2024 23:14:28 -0500
Subject: [PATCH] [libc] Allow each fucntion can have extra attributes by
 defining LLVM_LIBC_FUNCTION_ATTR_func macro.

---
 libc/src/__support/common.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
index 48c773fa02c176..489ca41770e998 100644
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -21,9 +21,24 @@
 #define LLVM_LIBC_FUNCTION_ATTR
 #endif
 
+// Allow each function `func` can have extra attributes specified by defining:
+// `LLVM_LIBC_FUNCTION_ATTR_func` macro, which should always start with
+// "LLVM_LIBC_EMPTY,"
+//
+// For example:
+// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, __attribute__((weak))
+#define LLVM_LIBC_EMPTY
+
+#define GET_SECOND(first, second, ...) second
+#define EXPAND_THEN_SECOND(name) GET_SECOND(name, LLVM_LIBC_EMPTY, )
+
+#define LLVM_LIBC_ATTR(name) EXPAND_THEN_SECOND(LLVM_LIBC_FUNCTION_ATTR_##name)
+#define EXPAND_ATTR(name) LLVM_LIBC_ATTR(name)
+
 // MacOS needs to be excluded because it does not support aliasing.
 #if defined(LIBC_COPT_PUBLIC_PACKAGING) && (!defined(__APPLE__))
 #define LLVM_LIBC_FUNCTION_IMPL(type, name, arglist)                           \
+  EXPAND_ATTR(name)                                                            \
   LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name)                       \
       __##name##_impl__ __asm__(#name);                                        \
   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \