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[libcxx] Support providing symbol suffix through compiler define #122570

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[libcxx] Support providing symbol suffix through compiler define #122570

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[libcxx] Support providing symbol suffix through compiler define
petrhosek Jan 11, 2025
f1e0e27
Append the suffix to the declaration
petrhosek Jan 15, 2025
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17 changes: 13 additions & 4 deletions libcxx/src/include/overridable_function.h
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,15 @@
// with this macro must be defined at global scope.
//

// When -funique-internal-linkage-names option is enabled, Clang will append a unique suffix
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@ldionne ldionne Jan 16, 2025

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It sounds like a generally missing feature that Clang doesn't provide any way to access that. I would prefer if we instead introduced either a macro that contains this suffix, or even better some kind of __builtin_symbol_name(name) that returns a string representing the symbol name for that entity while taking into account -funique-internal-linkage-names if needed.

That's something we could also use when defining operator new itself, i.e. we would not have to hardcode the mangled name in the macro. Similarly, we could refactor horrors like https://github.com/llvm/llvm-project/blob/main/libcxx/src/iostream.cpp#L22 where we hardcode mangled names, something @philnik777 was looking to do recently.

WDYT?

// `.uniq.<MD5 hash of the source file>` to all internal symbols. Since we cannot detect when
// this option is enabled or compute the source file hash from within the source file itself,
// the unique suffix needs to be supplied by the build system. The `_LIBCPP_SYMBOL_SUFFIX` can
// be used for that purpose.
#ifndef _LIBCPP_SYMBOL_SUFFIX
#define _LIBCPP_SYMBOL_SUFFIX
#endif

#if defined(_LIBCPP_OBJECT_FORMAT_MACHO)

_LIBCPP_BEGIN_NAMESPACE_STD
Expand All @@ -68,8 +77,8 @@ _LIBCPP_END_NAMESPACE_STD
# define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 1
# define _LIBCPP_OVERRIDABLE_FUNCTION(symbol, type, name, arglist) \
static __attribute__((used)) type symbol##_impl__ arglist __asm__("_" _LIBCPP_TOSTRING(symbol)); \
__asm__(".globl _" _LIBCPP_TOSTRING(symbol)); \
__asm__(".weak_definition _" _LIBCPP_TOSTRING(symbol)); \
__asm__(".globl _" _LIBCPP_TOSTRING(symbol) _LIBCPP_SYMBOL_SUFFIX); \
__asm__(".weak_definition _" _LIBCPP_TOSTRING(symbol) _LIBCPP_SYMBOL_SUFFIX); \
extern __typeof(symbol##_impl__) name __attribute__((weak_import)); \
_LIBCPP_BEGIN_NAMESPACE_STD \
template <> \
Expand All @@ -90,8 +99,8 @@ _LIBCPP_END_NAMESPACE_STD

# define _LIBCPP_CAN_DETECT_OVERRIDDEN_FUNCTION 1
# define _LIBCPP_OVERRIDABLE_FUNCTION(symbol, type, name, arglist) \
static type symbol##_impl__ arglist __asm__(_LIBCPP_TOSTRING(symbol##_impl__)); \
[[gnu::weak, gnu::alias(_LIBCPP_TOSTRING(symbol##_impl__))]] type name arglist; \
static type symbol##_impl__ arglist __asm__(_LIBCPP_TOSTRING(symbol##_impl__) _LIBCPP_SYMBOL_SUFFIX); \
[[gnu::weak, gnu::alias(_LIBCPP_TOSTRING(symbol##_impl__) _LIBCPP_SYMBOL_SUFFIX)]] type name arglist; \
_LIBCPP_BEGIN_NAMESPACE_STD \
template <> \
inline bool __is_function_overridden<static_cast<type(*) arglist>(name)>() { \
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