mirror of
https://github.com/FEX-Emu/FEX.git
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113 lines
3.4 KiB
C++
113 lines
3.4 KiB
C++
// SPDX-License-Identifier: MIT
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/*
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$info$
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tags: glue|x86-guest-code
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desc: Guest-side assembly helpers used by the backends
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$end_info$
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*/
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#include "Interface/Core/X86HelperGen.h"
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#include "FEXCore/Utils/AllocatorHooks.h"
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#include <FEXCore/Config/Config.h>
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#include <FEXCore/Utils/Allocator.h>
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#include <FEXHeaderUtils/Syscalls.h>
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#include <cstdint>
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#include <cstring>
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namespace FEXCore {
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constexpr size_t CODE_SIZE = 0x1000;
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X86GeneratedCode::X86GeneratedCode() {
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#ifdef _WIN32
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// No need to allocate anything in this config.
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#else
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// Allocate a page for our emulated guest
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CodePtr = AllocateGuestCodeSpace(CODE_SIZE);
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constexpr std::array<uint8_t, 2> SignalReturnCode = {
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0x0F, 0x37, // CALLBACKRET FEX Instruction
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};
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// Signal return handlers need to be bit-exact to what the Linux kernel provides in VDSO.
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// GDB and unwinding libraries key off of these instructions to understand if the stack frame is a signal frame or not.
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// This two code sections match exactly what libSegFault expects.
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//
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// Typically this handlers are provided by the 32-bit VDSO thunk library, but that isn't available in all cases.
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// Falling back to this generated code segment still allows a backtrace to work, just might not show
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// the symbol as VDSO since there is no ELF to parse.
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constexpr std::array<uint8_t, 9> sigreturn_32_code = {
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0x58, // pop eax
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0xb8, 0x77, 0x00, 0x00, 0x00, // mov eax, 0x77
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0xcd, 0x80, // int 0x80
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0x90, // nop
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};
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constexpr std::array<uint8_t, 7> rt_sigreturn_32_code = {
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0xb8, 0xad, 0x00, 0x00, 0x00, // mov eax, 0xad
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0xcd, 0x80, // int 0x80
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};
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CallbackReturn = reinterpret_cast<uint64_t>(CodePtr);
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sigreturn_32 = CallbackReturn + SignalReturnCode.size();
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rt_sigreturn_32 = sigreturn_32 + sigreturn_32_code.size();
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memcpy(reinterpret_cast<void*>(CallbackReturn), &SignalReturnCode.at(0), SignalReturnCode.size());
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memcpy(reinterpret_cast<void*>(sigreturn_32), &sigreturn_32_code.at(0), sigreturn_32_code.size());
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memcpy(reinterpret_cast<void*>(rt_sigreturn_32), &rt_sigreturn_32_code.at(0), rt_sigreturn_32_code.size());
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mprotect(CodePtr, CODE_SIZE, PROT_READ);
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#endif
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}
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X86GeneratedCode::~X86GeneratedCode() {
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#ifndef _WIN32
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FEXCore::Allocator::VirtualFree(CodePtr, CODE_SIZE);
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#endif
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}
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void* X86GeneratedCode::AllocateGuestCodeSpace(size_t Size) {
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#ifndef _WIN32
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FEX_CONFIG_OPT(Is64BitMode, IS64BIT_MODE);
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if (Is64BitMode()) {
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// 64bit mode can have its sigret handler anywhere
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return FEXCore::Allocator::VirtualAlloc(Size);
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}
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// First 64bit page
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constexpr uintptr_t LOCATION_MAX = 0x1'0000'0000;
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// 32bit mode
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// We need to have the sigret handler in the lower 32bits of memory space
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// Scan top down and try to allocate a location
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for (size_t Location = 0xFFFF'E000; Location != 0x0; Location -= 0x1000) {
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void *Ptr = ::mmap(reinterpret_cast<void*>(Location), Size, PROT_READ | PROT_WRITE, MAP_FIXED_NOREPLACE | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
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if (Ptr != MAP_FAILED &&
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reinterpret_cast<uintptr_t>(Ptr) >= LOCATION_MAX) {
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// Failed to map in the lower 32bits
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// Try again
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// Can happen in the case that host kernel ignores MAP_FIXED_NOREPLACE
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::munmap(Ptr, Size);
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continue;
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}
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if (Ptr != MAP_FAILED) {
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return Ptr;
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}
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}
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// Can't do anything about this
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// Here's hoping the application doesn't use signals
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return MAP_FAILED;
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#else
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return nullptr;
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#endif
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}
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}
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