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140 lines
5.0 KiB
C++
140 lines
5.0 KiB
C++
//===-- X86JITInfo.cpp - Implement the JIT interfaces for the X86 target --===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file implements the JIT interfaces for the X86 target.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "jit"
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#include "X86JITInfo.h"
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#include "X86Relocations.h"
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#include "llvm/CodeGen/MachineCodeEmitter.h"
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#include "llvm/Config/alloca.h"
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using namespace llvm;
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void *X86JITInfo::emitFunctionStub(void *Fn, MachineCodeEmitter &MCE) {
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MCE.startFunctionStub(6);
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MCE.emitByte(0xE8); // Call with 32 bit pc-rel destination...
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MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
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MCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
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return MCE.finishFunctionStub(0);
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}
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void X86JITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
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unsigned char *OldByte = (unsigned char *)Old;
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*OldByte++ = 0xE9; // Emit JMP opcode.
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unsigned *OldWord = (unsigned *)OldByte;
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unsigned NewAddr = (intptr_t)New;
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unsigned OldAddr = (intptr_t)OldWord;
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*OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
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}
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#ifdef _MSC_VER
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#pragma optimize("y", off)
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#endif
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/// JITCompilerFunction - This contains the address of the JIT function used to
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/// compile a function lazily.
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static TargetJITInfo::JITCompilerFn JITCompilerFunction;
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/// CompilationCallback - This is the target-specific function invoked by the
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/// function stub when we did not know the real target of a call. This function
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/// must locate the start of the stub or call site and pass it into the JIT
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/// compiler function.
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static void CompilationCallback() {
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#ifdef _MSC_VER
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unsigned *StackPtr, RetAddr;
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__asm mov StackPtr, ebp;
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__asm mov eax, DWORD PTR [ebp + 4];
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__asm mov RetAddr, eax;
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#else
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unsigned *StackPtr = (unsigned*)__builtin_frame_address(0);
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unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(0);
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// NOTE: __builtin_frame_address doesn't work if frame pointer elimination has
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// been performed. Having a variable sized alloca disables frame pointer
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// elimination currently, even if it's dead. This is a gross hack.
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alloca(10+(RetAddr >> 31));
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#endif
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assert(StackPtr[1] == RetAddr &&
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"Could not find return address on the stack!");
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// It's a stub if there is an interrupt marker after the call.
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bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
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// The call instruction should have pushed the return value onto the stack...
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RetAddr -= 4; // Backtrack to the reference itself...
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#if 0
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DEBUG(std::cerr << "In callback! Addr=" << (void*)RetAddr
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<< " ESP=" << (void*)StackPtr
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<< ": Resolving call to function: "
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<< TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
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#endif
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// Sanity check to make sure this really is a call instruction.
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assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
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unsigned NewVal = (intptr_t)JITCompilerFunction((void*)(intptr_t)RetAddr);
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// Rewrite the call target... so that we don't end up here every time we
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// execute the call.
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*(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
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if (isStub) {
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// If this is a stub, rewrite the call into an unconditional branch
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// instruction so that two return addresses are not pushed onto the stack
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// when the requested function finally gets called. This also makes the
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// 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
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((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
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}
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// Change the return address to reexecute the call instruction...
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StackPtr[1] -= 5;
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}
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#ifdef _MSC_VER
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#pragma optimize( "", on )
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#endif
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TargetJITInfo::LazyResolverFn
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X86JITInfo::getLazyResolverFunction(JITCompilerFn F) {
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JITCompilerFunction = F;
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return CompilationCallback;
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}
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/// relocate - Before the JIT can run a block of code that has been emitted,
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/// it must rewrite the code to contain the actual addresses of any
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/// referenced global symbols.
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void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
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unsigned NumRelocs) {
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for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
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void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
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intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
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switch ((X86::RelocationType)MR->getRelocationType()) {
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case X86::reloc_pcrel_word:
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// PC relative relocation, add the relocated value to the value already in
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// memory, after we adjust it for where the PC is.
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ResultPtr = ResultPtr-(intptr_t)RelocPos-4;
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*((intptr_t*)RelocPos) += ResultPtr;
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break;
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case X86::reloc_absolute_word:
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// Absolute relocation, just add the relocated value to the value already
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// in memory.
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*((intptr_t*)RelocPos) += ResultPtr;
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break;
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}
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}
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}
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