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"
15 #include "X86JITInfo.h"
16 #include "X86Relocations.h"
17 #include "llvm/CodeGen/MachineCodeEmitter.h"
18 #include "llvm/Config/alloca.h"
23 void X86JITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
24 unsigned char *OldByte = (unsigned char *)Old;
25 *OldByte++ = 0xE9; // Emit JMP opcode.
26 unsigned *OldWord = (unsigned *)OldByte;
27 unsigned NewAddr = (intptr_t)New;
28 unsigned OldAddr = (intptr_t)OldWord;
29 *OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
33 /// JITCompilerFunction - This contains the address of the JIT function used to
34 /// compile a function lazily.
35 static TargetJITInfo::JITCompilerFn JITCompilerFunction;
37 // Provide a wrapper for X86CompilationCallback2 that saves non-traditional
38 // callee saved registers, for the fastcc calling convention.
40 #if defined(__i386__) || defined(i386) || defined(_M_IX86)
42 void X86CompilationCallback(void);
46 #if defined(__CYGWIN__) || defined(__APPLE__)
47 ".globl _X86CompilationCallback\n"
48 "_X86CompilationCallback:\n"
50 ".globl X86CompilationCallback\n"
51 "X86CompilationCallback:\n"
54 "movl %esp, %ebp\n" // Standard prologue
56 "pushl %edx\n" // save EAX/EDX
57 #if defined(__CYGWIN__) || defined(__APPLE__)
58 "call _X86CompilationCallback2\n"
60 "call X86CompilationCallback2\n"
67 extern "C" void *_AddressOfReturnAddress(void);
68 #pragma intrinsic(_AddressOfReturnAddress)
70 void X86CompilationCallback2(void);
72 _declspec(naked) void X86CompilationCallback(void) {
76 call X86CompilationCallback2
84 #else // Not an i386 host
85 void X86CompilationCallback() {
86 std::cerr << "Cannot call X86CompilationCallback() on a non-x86 arch!\n";
92 /// X86CompilationCallback - This is the target-specific function invoked by the
93 /// function stub when we did not know the real target of a call. This function
94 /// must locate the start of the stub or call site and pass it into the JIT
95 /// compiler function.
96 extern "C" void X86CompilationCallback2() {
98 assert(sizeof(size_t) == 4); // FIXME: handle Win64
99 unsigned *RetAddrLoc = (unsigned *)_AddressOfReturnAddress();
100 RetAddrLoc += 3; // skip over ret addr, edx, eax
101 unsigned RetAddr = *RetAddrLoc;
103 unsigned *StackPtr = (unsigned*)__builtin_frame_address(1);
104 unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(1);
105 unsigned *RetAddrLoc = &StackPtr[1];
107 // NOTE: __builtin_frame_address doesn't work if frame pointer elimination has
108 // been performed. Having a variable sized alloca disables frame pointer
109 // elimination currently, even if it's dead. This is a gross hack.
110 alloca(10+(RetAddr >> 31));
113 assert(*RetAddrLoc == RetAddr &&
114 "Could not find return address on the stack!");
116 // It's a stub if there is an interrupt marker after the call.
117 bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
119 // The call instruction should have pushed the return value onto the stack...
120 RetAddr -= 4; // Backtrack to the reference itself...
123 DEBUG(std::cerr << "In callback! Addr=" << (void*)RetAddr
124 << " ESP=" << (void*)StackPtr
125 << ": Resolving call to function: "
126 << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
129 // Sanity check to make sure this really is a call instruction.
130 assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
132 unsigned NewVal = (intptr_t)JITCompilerFunction((void*)(intptr_t)RetAddr);
134 // Rewrite the call target... so that we don't end up here every time we
136 *(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
139 // If this is a stub, rewrite the call into an unconditional branch
140 // instruction so that two return addresses are not pushed onto the stack
141 // when the requested function finally gets called. This also makes the
142 // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
143 ((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
146 // Change the return address to reexecute the call instruction...
150 TargetJITInfo::LazyResolverFn
151 X86JITInfo::getLazyResolverFunction(JITCompilerFn F) {
152 JITCompilerFunction = F;
153 return X86CompilationCallback;
156 void *X86JITInfo::emitFunctionStub(void *Fn, MachineCodeEmitter &MCE) {
157 if (Fn != X86CompilationCallback) {
158 MCE.startFunctionStub(5);
160 MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
161 return MCE.finishFunctionStub(0);
164 MCE.startFunctionStub(6);
165 MCE.emitByte(0xE8); // Call with 32 bit pc-rel destination...
167 MCE.emitWord((intptr_t)Fn-MCE.getCurrentPCValue()-4);
169 MCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
170 return MCE.finishFunctionStub(0);
173 /// relocate - Before the JIT can run a block of code that has been emitted,
174 /// it must rewrite the code to contain the actual addresses of any
175 /// referenced global symbols.
176 void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
177 unsigned NumRelocs, unsigned char* GOTBase) {
178 for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
179 void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
180 intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
181 switch ((X86::RelocationType)MR->getRelocationType()) {
182 case X86::reloc_pcrel_word:
183 // PC relative relocation, add the relocated value to the value already in
184 // memory, after we adjust it for where the PC is.
185 ResultPtr = ResultPtr-(intptr_t)RelocPos-4;
186 *((intptr_t*)RelocPos) += ResultPtr;
188 case X86::reloc_absolute_word:
189 // Absolute relocation, just add the relocated value to the value already
191 *((intptr_t*)RelocPos) += ResultPtr;