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[libc] Allow each function can have extra attributes by defining LLVM_LIBC_FUNCTION_ATTR_func macro. #116160

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Merged
merged 4 commits into from
Nov 20, 2024
Merged

[libc] Allow each function can have extra attributes by defining LLVM_LIBC_FUNCTION_ATTR_func macro. #116160

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44637f4
[libc] Allow each fucntion can have extra attributes by defining LLVM…
lntue Nov 14, 2024
ed162f5
Address comments.
lntue Nov 19, 2024
7a1a3c5
Fix bazel build.
lntue Nov 19, 2024
fa25a75
Address comments.
lntue Nov 20, 2024
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16 changes: 16 additions & 0 deletions libc/src/__support/common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -21,9 +21,25 @@
#define LLVM_LIBC_FUNCTION_ATTR
#endif

// 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, "
//
// 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)

// 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) \
LLVM_LIBC_ATTR(name) \
LLVM_LIBC_FUNCTION_ATTR decltype(LIBC_NAMESPACE::name) \
__##name##_impl__ __asm__(#name); \
decltype(LIBC_NAMESPACE::name) name [[gnu::alias(#name)]]; \
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16 changes: 10 additions & 6 deletions utils/bazel/llvm-project-overlay/libc/libc_build_rules.bzl
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Original file line number Diff line number Diff line change
Expand Up @@ -59,7 +59,7 @@ def libc_function(
srcs,
weak = False,
copts = None,
local_defines = None,
local_defines = [],
**kwargs):
"""Add target for a libc function.

Expand Down Expand Up @@ -108,16 +108,20 @@ def libc_function(
name = libc_internal_target(name),
srcs = srcs,
copts = copts,
local_defines = local_defines,
**kwargs
)

# 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)]
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='[[gnu::visibility(\"default\")]]'"]
+ func_attrs)
_libc_library(
name = name,
hidden = True,
Expand Down
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