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"
24 extern "C" void *_AddressOfReturnAddress(void);
25 #pragma intrinsic(_AddressOfReturnAddress)
28 void X86JITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
29 unsigned char *OldByte = (unsigned char *)Old;
30 *OldByte++ = 0xE9; // Emit JMP opcode.
31 unsigned *OldWord = (unsigned *)OldByte;
32 unsigned NewAddr = (intptr_t)New;
33 unsigned OldAddr = (intptr_t)OldWord;
34 *OldWord = NewAddr - OldAddr - 4; // Emit PC-relative addr of New code.
38 /// JITCompilerFunction - This contains the address of the JIT function used to
39 /// compile a function lazily.
40 static TargetJITInfo::JITCompilerFn JITCompilerFunction;
42 // Provide a wrapper for X86CompilationCallback2 that saves non-traditional
43 // callee saved registers, for the fastcc calling convention.
45 #if defined(__i386__) || defined(i386) || defined(_M_IX86)
47 void X86CompilationCallback(void);
51 #if defined(__CYGWIN__) || defined(__APPLE__) || defined(__MINGW32__)
52 ".globl _X86CompilationCallback\n"
53 "_X86CompilationCallback:\n"
55 ".globl X86CompilationCallback\n"
56 "X86CompilationCallback:\n"
59 "movl %esp, %ebp\n" // Standard prologue
61 "pushl %edx\n" // save EAX/EDX
62 #if defined(__CYGWIN__) || defined(__MINGW32__)
63 "call _X86CompilationCallback2\n"
64 #elif defined(__APPLE__)
65 "movl 4(%ebp), %eax\n" // load the address of return address
66 "movl $24, %edx\n" // if the opcode of the instruction at the
67 "cmpb $-51, (%eax)\n" // return address is our 0xCD marker, then
68 "movl $12, %eax\n" // subtract 24 from %esp to realign it to 16
69 "cmovne %eax, %edx\n" // bytes after the push of edx, the amount to.
70 "subl %edx, %esp\n" // the push of edx to keep it aligned.
71 "pushl %edx\n" // subtract. Otherwise, subtract 12 bytes after
72 "call _X86CompilationCallback2\n"
76 "call X86CompilationCallback2\n"
83 void X86CompilationCallback2(void);
85 _declspec(naked) void X86CompilationCallback(void) {
89 call X86CompilationCallback2
97 #else // Not an i386 host
98 void X86CompilationCallback() {
99 std::cerr << "Cannot call X86CompilationCallback() on a non-x86 arch!\n";
105 /// X86CompilationCallback - This is the target-specific function invoked by the
106 /// function stub when we did not know the real target of a call. This function
107 /// must locate the start of the stub or call site and pass it into the JIT
108 /// compiler function.
109 extern "C" void X86CompilationCallback2() {
111 assert(sizeof(size_t) == 4); // FIXME: handle Win64
112 unsigned *RetAddrLoc = (unsigned *)_AddressOfReturnAddress();
113 RetAddrLoc += 3; // skip over ret addr, edx, eax
114 unsigned RetAddr = *RetAddrLoc;
116 unsigned *StackPtr = (unsigned*)__builtin_frame_address(1);
117 unsigned RetAddr = (unsigned)(intptr_t)__builtin_return_address(1);
118 unsigned *RetAddrLoc = &StackPtr[1];
120 // NOTE: __builtin_frame_address doesn't work if frame pointer elimination has
121 // been performed. Having a variable sized alloca disables frame pointer
122 // elimination currently, even if it's dead. This is a gross hack.
123 alloca(10+(RetAddr >> 31));
126 assert(*RetAddrLoc == RetAddr &&
127 "Could not find return address on the stack!");
129 // It's a stub if there is an interrupt marker after the call.
130 bool isStub = ((unsigned char*)(intptr_t)RetAddr)[0] == 0xCD;
132 // The call instruction should have pushed the return value onto the stack...
133 RetAddr -= 4; // Backtrack to the reference itself...
136 DEBUG(std::cerr << "In callback! Addr=" << (void*)RetAddr
137 << " ESP=" << (void*)StackPtr
138 << ": Resolving call to function: "
139 << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
142 // Sanity check to make sure this really is a call instruction.
143 assert(((unsigned char*)(intptr_t)RetAddr)[-1] == 0xE8 &&"Not a call instr!");
145 unsigned NewVal = (intptr_t)JITCompilerFunction((void*)(intptr_t)RetAddr);
147 // Rewrite the call target... so that we don't end up here every time we
149 *(unsigned*)(intptr_t)RetAddr = NewVal-RetAddr-4;
152 // If this is a stub, rewrite the call into an unconditional branch
153 // instruction so that two return addresses are not pushed onto the stack
154 // when the requested function finally gets called. This also makes the
155 // 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
156 ((unsigned char*)(intptr_t)RetAddr)[-1] = 0xE9;
159 // Change the return address to reexecute the call instruction...
163 TargetJITInfo::LazyResolverFn
164 X86JITInfo::getLazyResolverFunction(JITCompilerFn F) {
165 JITCompilerFunction = F;
166 return X86CompilationCallback;
169 void *X86JITInfo::emitFunctionStub(void *Fn, MachineCodeEmitter &MCE) {
170 if (Fn != (void*)X86CompilationCallback) {
171 MCE.startFunctionStub(5);
173 MCE.emitWordLE((intptr_t)Fn-MCE.getCurrentPCValue()-4);
174 return MCE.finishFunctionStub(0);
177 MCE.startFunctionStub(6);
178 MCE.emitByte(0xE8); // Call with 32 bit pc-rel destination...
180 MCE.emitWordLE((intptr_t)Fn-MCE.getCurrentPCValue()-4);
182 MCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
183 return MCE.finishFunctionStub(0);
186 /// relocate - Before the JIT can run a block of code that has been emitted,
187 /// it must rewrite the code to contain the actual addresses of any
188 /// referenced global symbols.
189 void X86JITInfo::relocate(void *Function, MachineRelocation *MR,
190 unsigned NumRelocs, unsigned char* GOTBase) {
191 for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
192 void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
193 intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
194 switch ((X86::RelocationType)MR->getRelocationType()) {
195 case X86::reloc_pcrel_word:
196 // PC relative relocation, add the relocated value to the value already in
197 // memory, after we adjust it for where the PC is.
198 ResultPtr = ResultPtr-(intptr_t)RelocPos-4;
199 *((intptr_t*)RelocPos) += ResultPtr;
201 case X86::reloc_absolute_word:
202 // Absolute relocation, just add the relocated value to the value already
204 *((intptr_t*)RelocPos) += ResultPtr;