mirror of
https://github.com/RGBCube/serenity
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2af028132a
Doesn't use them in libc headers so that those don't have to pull in AK/Platform.h. AK_COMPILER_GCC is set _only_ for gcc, not for clang too. (__GNUC__ is defined in clang builds as well.) Using AK_COMPILER_GCC simplifies things some. AK_COMPILER_CLANG isn't as much of a win, other than that it's consistent with AK_COMPILER_GCC.
59 lines
1.7 KiB
C++
59 lines
1.7 KiB
C++
/*
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* Copyright (c) 2022, Daniel Bertalan <dani@danielbertalan.dev>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include <AK/Types.h>
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#include <cpuid.h>
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#include <string.h>
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extern "C" {
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extern void* memset_sse2(void*, int, size_t);
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extern void* memset_sse2_erms(void*, int, size_t);
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constexpr u32 tcg_signature_ebx = 0x54474354;
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constexpr u32 tcg_signature_ecx = 0x43544743;
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constexpr u32 tcg_signature_edx = 0x47435447;
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// Bit 9 of ebx in cpuid[eax = 7] indicates support for "Enhanced REP MOVSB/STOSB"
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constexpr u32 cpuid_7_ebx_bit_erms = 1 << 9;
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namespace {
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[[gnu::used]] decltype(&memset) resolve_memset()
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{
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u32 eax, ebx, ecx, edx;
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__cpuid(0x40000000, eax, ebx, ecx, edx);
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bool is_tcg = ebx == tcg_signature_ebx && ecx == tcg_signature_ecx && edx == tcg_signature_edx;
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// Although TCG reports ERMS support, testing shows that rep stosb performs strictly worse than
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// SSE copies on all data sizes except <= 4 bytes.
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if (is_tcg)
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return memset_sse2;
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__cpuid_count(7, 0, eax, ebx, ecx, edx);
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if (ebx & cpuid_7_ebx_bit_erms)
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return memset_sse2_erms;
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return memset_sse2;
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}
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}
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#if !defined(AK_COMPILER_CLANG) && !defined(_DYNAMIC_LOADER)
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[[gnu::ifunc("resolve_memset")]] void* memset(void*, int, size_t);
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#else
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// DynamicLoader can't self-relocate IFUNCs.
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// FIXME: There's a circular dependency between LibC and libunwind when built with Clang,
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// so the IFUNC resolver could be called before LibC has been relocated, returning bogus addresses.
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void* memset(void* dest_ptr, int c, size_t n)
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{
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static decltype(&memset) s_impl = nullptr;
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if (s_impl == nullptr)
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s_impl = resolve_memset();
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return s_impl(dest_ptr, c, n);
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}
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#endif
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}
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