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[libc++][NFC] Refactor _LIBCPP_OVERRIDABLE_FUNCTION to be a normal attribute macro (#174964)

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Currently `_LIBCPP_OVERRIDABLE_FUNCTION` takes the return type, function
name and argument list, but simply constructs the function and adds
attributes without modifying the signature in any way. We can replace
this with a normal attribute macro, making the signature easier to read
and simpler to understand what's actually going on. Since it's an
internal macro we can also drop the `_LIBCPP_` prefix.
This commit is contained in:
Nikolas Klauser 2026-01-09 12:07:42 +01:00 committed by GitHub
parent b6bfb199cc
commit a5cab90071
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GPG key ID: B5690EEEBB952194
3 changed files with 16 additions and 18 deletions
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18
libcxx/src/include/overridable_function.h
View file

@ -29,12 +29,12 @@
// This is a low-level utility which does not work on all platforms, since it needs
// to make assumptions about the object file format in use. Furthermore, it requires
// the "base definition" of the function (the one we want to check whether it has been
// overridden) to be defined using the _LIBCPP_OVERRIDABLE_FUNCTION macro.
// overridden) to be defined using the OVERRIDABLE_FUNCTION macro.
//
// This currently works with Mach-O files (used on Darwin) and with ELF files (used on Linux
// and others). On platforms where we know how to implement this detection, the macro
// _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION is defined to 1, and it is defined to 0 on
// other platforms. The _LIBCPP_OVERRIDABLE_FUNCTION macro is defined to perform a normal
// other platforms. The OVERRIDABLE_FUNCTION macro is defined to perform a normal
// function definition on unsupported platforms so that it can be used to define functions
// regardless of whether detection is actually supported.
//
@ -44,7 +44,7 @@
// Let's say we want to check whether a weak function `f` has been overridden by the user.
// The general mechanism works by placing `f`'s definition (in the libc++ built library)
// inside a special section, which we do using the `__section__` attribute via the
// _LIBCPP_OVERRIDABLE_FUNCTION macro.
// OVERRIDABLE_FUNCTION macro.
//
// Then, when comes the time to check whether the function has been overridden, we take
// the address of the function and we check whether it falls inside the special function
@ -66,11 +66,10 @@
#if defined(_LIBCPP_OBJECT_FORMAT_MACHO)
# define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 1
# define _LIBCPP_OVERRIDABLE_FUNCTION(type, name, arglist) \
__attribute__((__section__("__TEXT,__lcxx_override,regular,pure_instructions"))) _LIBCPP_WEAK type name arglist
# define OVERRIDABLE_FUNCTION \
__attribute__((__section__("__TEXT,__lcxx_override,regular,pure_instructions"))) _LIBCPP_WEAK
_LIBCPP_BEGIN_NAMESPACE_STD
template <typename T, T* _Func>
_LIBCPP_BEGIN_NAMESPACE_STD template <typename T, T* _Func>
_LIBCPP_HIDE_FROM_ABI inline bool __is_function_overridden() noexcept {
// Declare two dummy bytes and give them these special `__asm` values. These values are
// defined by the linker, which means that referring to `&__lcxx_override_start` will
@ -100,8 +99,7 @@ _LIBCPP_END_NAMESPACE_STD
#elif defined(_LIBCPP_OBJECT_FORMAT_ELF) && !defined(__NVPTX__)
# define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 1
# define _LIBCPP_OVERRIDABLE_FUNCTION(type, name, arglist) \
__attribute__((__section__("__lcxx_override"))) _LIBCPP_WEAK type name arglist
# define OVERRIDABLE_FUNCTION __attribute__((__section__("__lcxx_override"))) _LIBCPP_WEAK
// This is very similar to what we do for Mach-O above. The ELF linker will implicitly define
// variables with those names corresponding to the start and the end of the section.
@ -129,7 +127,7 @@ _LIBCPP_END_NAMESPACE_STD
#else
# define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 0
# define _LIBCPP_OVERRIDABLE_FUNCTION(type, name, arglist) _LIBCPP_WEAK type name arglist
# define OVERRIDABLE_FUNCTION _LIBCPP_WEAK
#endif

8
libcxx/src/new.cpp
View file

@ -43,7 +43,7 @@ static void* operator_new_impl(std::size_t size) {
return p;
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new, (std::size_t size)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new(std::size_t size) _THROW_BAD_ALLOC {
void* p = operator_new_impl(size);
if (p == nullptr)
__throw_bad_alloc_shim();
@ -74,7 +74,7 @@ _LIBCPP_WEAK void* operator new(size_t size, const std::nothrow_t&) noexcept {
# endif
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new[], (size_t size)) _THROW_BAD_ALLOC { return ::operator new(size); }
OVERRIDABLE_FUNCTION void* operator new[](size_t size) _THROW_BAD_ALLOC { return ::operator new(size); }
_LIBCPP_WEAK void* operator new[](size_t size, const std::nothrow_t&) noexcept {
# if !_LIBCPP_HAS_EXCEPTIONS
@ -134,7 +134,7 @@ static void* operator_new_aligned_impl(std::size_t size, std::align_val_t alignm
return p;
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new, (std::size_t size, std::align_val_t alignment)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
void* p = operator_new_aligned_impl(size, alignment);
if (p == nullptr)
__throw_bad_alloc_shim();
@ -165,7 +165,7 @@ _LIBCPP_WEAK void* operator new(size_t size, std::align_val_t alignment, const s
# endif
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new[], (size_t size, std::align_val_t alignment)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new[](size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
return ::operator new(size, alignment);
}

8
libcxxabi/src/stdlib_new_delete.cpp
View file

@ -63,7 +63,7 @@ static void* operator_new_impl(std::size_t size) {
return p;
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new, (std::size_t size)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new(std::size_t size) _THROW_BAD_ALLOC {
void* p = operator_new_impl(size);
if (p == nullptr)
__throw_bad_alloc_shim();
@ -94,7 +94,7 @@ _LIBCPP_WEAK void* operator new(size_t size, const std::nothrow_t&) noexcept {
#endif
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new[], (size_t size)) _THROW_BAD_ALLOC { return ::operator new(size); }
OVERRIDABLE_FUNCTION void* operator new[](size_t size) _THROW_BAD_ALLOC { return ::operator new(size); }
_LIBCPP_WEAK void* operator new[](size_t size, const std::nothrow_t&) noexcept {
#if !_LIBCPP_HAS_EXCEPTIONS
@ -154,7 +154,7 @@ static void* operator_new_aligned_impl(std::size_t size, std::align_val_t alignm
return p;
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new, (std::size_t size, std::align_val_t alignment)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new(std::size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
void* p = operator_new_aligned_impl(size, alignment);
if (p == nullptr)
__throw_bad_alloc_shim();
@ -185,7 +185,7 @@ _LIBCPP_WEAK void* operator new(size_t size, std::align_val_t alignment, const s
# endif
}
_LIBCPP_OVERRIDABLE_FUNCTION(void*, operator new[], (size_t size, std::align_val_t alignment)) _THROW_BAD_ALLOC {
OVERRIDABLE_FUNCTION void* operator new[](size_t size, std::align_val_t alignment) _THROW_BAD_ALLOC {
return ::operator new(size, alignment);
}