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/*
* Copyright (c) 2022, Daniel Bertalan <dani@danielbertalan.dev>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include <AK/Types.h>
#include <cpuid.h>
#include <string.h>
extern "C" {
extern void* memset_sse2(void*, int, size_t);
extern void* memset_sse2_erms(void*, int, size_t);
constexpr u32 tcg_signature_ebx = 0x54474354;
constexpr u32 tcg_signature_ecx = 0x43544743;
constexpr u32 tcg_signature_edx = 0x47435447;
// Bit 9 of ebx in cpuid[eax = 7] indicates support for "Enhanced REP MOVSB/STOSB"
constexpr u32 cpuid_7_ebx_bit_erms = 1 << 9;
namespace {
[[gnu::used]] decltype(&memset) resolve_memset()
{
u32 eax, ebx, ecx, edx;
__cpuid(0x40000000, eax, ebx, ecx, edx);
bool is_tcg = ebx == tcg_signature_ebx && ecx == tcg_signature_ecx && edx == tcg_signature_edx;
// Although TCG reports ERMS support, testing shows that rep stosb performs strictly worse than
// SSE copies on all data sizes except <= 4 bytes.
if (is_tcg)
return memset_sse2;
__cpuid_count(7, 0, eax, ebx, ecx, edx);
if (ebx & cpuid_7_ebx_bit_erms)
return memset_sse2_erms;
return memset_sse2;
}
}
#if !defined(__clang__) && !defined(_DYNAMIC_LOADER)
[[gnu::ifunc("resolve_memset")]] void* memset(void*, int, size_t);
#else
// DynamicLoader can't self-relocate IFUNCs.
// FIXME: There's a circular dependency between LibC and libunwind when built with Clang,
// so the IFUNC resolver could be called before LibC has been relocated, returning bogus addresses.
void* memset(void* dest_ptr, int c, size_t n)
{
static decltype(&memset) s_impl = nullptr;
if (s_impl == nullptr)
s_impl = resolve_memset();
return s_impl(dest_ptr, c, n);
}
#endif
}
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