1 //===-- X86JITInfo.cpp - Implement the JIT interfaces for the X86 target --===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the JIT interfaces for the X86 target.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "jit"
16 #include "X86JITInfo.h"
17 #include "X86Relocations.h"
18 #include "llvm/CodeGen/MachineCodeEmitter.h"
19 #include "llvm/Config/alloca.h"
22 void X86JITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
23 unsigned char *OldByte = (unsigned char *)Old;
24 *OldByte++ = 0xE9; // Emit JMP opcode.
25 unsigned *OldWord = (unsigned *)OldByte;
26 unsigned NewAddr = (intptr_t)New;
27 unsigned OldAddr = (intptr_t)OldWord;
28 *OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
32 /// JITCompilerFunction - This contains the address of the JIT function used to
33 /// compile a function lazily.
34 static TargetJITInfo::JITCompilerFn JITCompilerFunction;
36 // Provide a wrapper for X86CompilationCallback2 that saves non-traditional
37 // callee saved registers, for the fastcc calling convention.
39 #if defined(__i386__) || defined(i386) || defined(_M_IX86)
41 void X86CompilationCallback(void);
45 ".globl X86CompilationCallback\n"
46 "X86CompilationCallback:\n"
48 "movl %esp, %ebp\n" // Standard prologue
50 "pushl %edx\n" // save EAX/EDX
51 "call X86CompilationCallback2\n"
57 extern "C" void *_AddressOfReturnAddress(void);
58 #pragma intrinsic(_AddressOfReturnAddress)
60 void X86CompilationCallback2(void);
62 _declspec(naked) void X86CompilationCallback(void) {
66 call X86CompilationCallback2
76 void X86CompilationCallback() {
77 assert(0 && "This is not a X86, you can't execute this!");
83 /// X86CompilationCallback - This is the target-specific function invoked by the
84 /// function stub when we did not know the real target of a call. This function
85 /// must locate the start of the stub or call site and pass it into the JIT
86 /// compiler function.
87 extern "C" void X86CompilationCallback2() {
89 assert(sizeof(size_t) == 4); // FIXME: handle Win64
90 unsigned *RetAddrLoc = (unsigned *)_AddressOfReturnAddress();
91 RetAddrLoc += 3; // skip over ret addr, edx, eax
92 unsigned RetAddr = *RetAddrLoc;
94 unsigned *StackPtr = (unsigned*)__builtin_frame_address(1);
95 unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(1);
96 unsigned *RetAddrLoc = &StackPtr[1];
98 // NOTE: __builtin_frame_address doesn't work if frame pointer elimination has
99 // been performed. Having a variable sized alloca disables frame pointer
100 // elimination currently, even if it's dead. This is a gross hack.
101 alloca(10+(RetAddr >> 31));
104 assert(*RetAddrLoc == RetAddr &&
105 "Could not find return address on the stack!");
107 // It's a stub if there is an interrupt marker after the call.
108 bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
110 // The call instruction should have pushed the return value onto the stack...
111 RetAddr -= 4; // Backtrack to the reference itself...
114 DEBUG(std::cerr << "In callback! Addr=" << (void*)RetAddr
115 << " ESP=" << (void*)StackPtr
116 << ": Resolving call to function: "
117 << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
120 // Sanity check to make sure this really is a call instruction.
121 assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
123 unsigned NewVal = (intptr_t)JITCompilerFunction((void*)(intptr_t)RetAddr);
125 // Rewrite the call target... so that we don't end up here every time we
127 *(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
130 // If this is a stub, rewrite the call into an unconditional branch
131 // instruction so that two return addresses are not pushed onto the stack
132 // when the requested function finally gets called. This also makes the
133 // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
134 ((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
137 // Change the return address to reexecute the call instruction...
141 TargetJITInfo::LazyResolverFn
142 X86JITInfo::getLazyResolverFunction(JITCompilerFn F) {
143 JITCompilerFunction = F;
144 return X86CompilationCallback;
147 void *X86JITInfo::emitFunctionStub(void *Fn, MachineCodeEmitter &MCE) {
148 if (Fn != X86CompilationCallback) {
149 MCE.startFunctionStub(5);
151 MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
152 return MCE.finishFunctionStub(0);
155 MCE.startFunctionStub(6);
156 MCE.emitByte(0xE8); // Call with 32 bit pc-rel destination...
158 MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
160 MCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
161 return MCE.finishFunctionStub(0);
164 /// relocate - Before the JIT can run a block of code that has been emitted,
165 /// it must rewrite the code to contain the actual addresses of any
166 /// referenced global symbols.
167 void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
168 unsigned NumRelocs) {
169 for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
170 void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
171 intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
172 switch ((X86::RelocationType)MR->getRelocationType()) {
173 case X86::reloc_pcrel_word:
174 // PC relative relocation, add the relocated value to the value already in
175 // memory, after we adjust it for where the PC is.
176 ResultPtr = ResultPtr-(intptr_t)RelocPos-4;
177 *((intptr_t*)RelocPos) += ResultPtr;
179 case X86::reloc_absolute_word:
180 // Absolute relocation, just add the relocated value to the value already
182 *((intptr_t*)RelocPos) += ResultPtr;