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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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[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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15 changes: 15 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 +21,24 @@
#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))
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@nickdesaulniers nickdesaulniers Nov 19, 2024

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Suggested change
// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, __attribute__((weak))
// #define LLVM_LIBC_FUNCTION_ATTR_memcpy LLVM_LIBC_EMPTY, [[gnu::weak]]

Let's encourage the usage of the C++11/C23 style attribute syntax, rather than the GNU C extension syntax.

Though, don't we expect this to be used by the command line cmake invocation? Perhaps an example of that in this comment, or moving our bazel files over to use that would be welcome additions to this PR?

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@nickdesaulniers nickdesaulniers Nov 19, 2024

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Perhaps worth documenting any new command line options in docs/dev/implementation_standard.rst.

#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)
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@vonosmas vonosmas Nov 19, 2024

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I don't think you need EXPAND_ATTR and can just use LLVM_LIBC_ATTR below?

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@lntue lntue Nov 19, 2024

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I think you're right, EXPAND_ATTR is not needed.


// 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)]]; \
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