[libc-commits] [libc] [llvm] [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 1/2] [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)]];                   \

>From ed162f5748644f669da644e326920c7e7d48341d Mon Sep 17 00:00:00 2001
From: Tue Ly <lntue at google.com>
Date: Tue, 19 Nov 2024 17:18:50 -0500
Subject: [PATCH 2/2] Address comments.

---
 libc/src/__support/common.h                      | 13 +++++++------
 .../libc/libc_build_rules.bzl                    | 16 +++++++++++-----
 2 files changed, 18 insertions(+), 11 deletions(-)

diff --git a/libc/src/__support/common.h b/libc/src/__support/common.h
index 489ca41770e998..582b53f056b9f0 100644
--- a/libc/src/__support/common.h
+++ b/libc/src/__support/common.h
@@ -21,24 +21,25 @@
 #define LLVM_LIBC_FUNCTION_ATTR
 #endif
 
-// Allow each function `func` can have extra attributes specified by defining:
+// Allow each function `func` to have extra attributes specified by defining:
 // `LLVM_LIBC_FUNCTION_ATTR_func` macro, which should always start with
-// "LLVM_LIBC_EMPTY,"
+// "LLVM_LIBC_EMPTY, "
 //
-// For example:
-// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, __attribute__((weak))
+// For examples:
+// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, [[gnu::weak]]
+// #define LLVM_LIBC_FUNCTION_ATTR_memchr LLVM_LIBC_EMPTY, [[gnu::weak]]       \
+//                                        [[gnu::visibility("default")]]
 #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_ATTR(name)                                                         \
   LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name)                       \
       __##name##_impl__ __asm__(#name);                                        \
   decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]];                   \
diff --git a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
index 9dc25f95b8e3f1..e95b65397c66ef 100644
--- a/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
+++ b/utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
@@ -113,11 +113,17 @@ def libc_function(
 
     # This second target is the llvm libc C function with either a default or hidden visibility.
     # All other functions are hidden.
-    func_attrs = ["__attribute__((visibility(\"default\")))"]
-    if weak:
-        func_attrs = func_attrs + ["__attribute__((weak))"]
-    local_defines = local_defines or ["LIBC_COPT_PUBLIC_PACKAGING"]
-    local_defines = local_defines + ["LLVM_LIBC_FUNCTION_ATTR='%s'" % " ".join(func_attrs)]
+    global_func_attrs = [
+        "[[gnu::visibility("default")]]",
+    ]
+    func_attrs = [
+        "LLVM_LIBC_FUNCTION_ATTR_" + name + "='LLVM_LIBC_EMPTY, [[gnu::weak]]'",
+    ] if weak else []
+        
+    local_defines = (local_defines
+                    + ["LIBC_COPT_PUBLIC_PACKAGING"]
+                    + ["LLVM_LIBC_FUNCTION_ATTR='%s'" % " ".join(global_func_attrs)]
+                    + func_attrs)
     _libc_library(
         name = name,
         hidden = True,