ARMJITInfo.cpp revision ea6e03699e9e0cbe6aaf537ac7f4dee443ee42d0
1//===-- ARMJITInfo.cpp - Implement the JIT interfaces for the ARM target --===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements the JIT interfaces for the ARM target. 11// 12//===----------------------------------------------------------------------===// 13 14#define DEBUG_TYPE "jit" 15#include "ARMJITInfo.h" 16#include "ARMRelocations.h" 17#include "ARMSubtarget.h" 18#include "llvm/Function.h" 19#include "llvm/CodeGen/MachineCodeEmitter.h" 20#include "llvm/Config/alloca.h" 21#include "llvm/Support/Streams.h" 22#include "llvm/System/Memory.h" 23#include <cstdlib> 24using namespace llvm; 25 26void ARMJITInfo::replaceMachineCodeForFunction(void *Old, void *New) { 27 abort(); 28} 29 30/// JITCompilerFunction - This contains the address of the JIT function used to 31/// compile a function lazily. 32static TargetJITInfo::JITCompilerFn JITCompilerFunction; 33 34// Get the ASMPREFIX for the current host. This is often '_'. 35#ifndef __USER_LABEL_PREFIX__ 36#define __USER_LABEL_PREFIX__ 37#endif 38#define GETASMPREFIX2(X) #X 39#define GETASMPREFIX(X) GETASMPREFIX2(X) 40#define ASMPREFIX GETASMPREFIX(__USER_LABEL_PREFIX__) 41 42// CompilationCallback stub - We can't use a C function with inline assembly in 43// it, because we the prolog/epilog inserted by GCC won't work for us (we need 44// to preserve more context and manipulate the stack directly). Instead, 45// write our own wrapper, which does things our way, so we have complete 46// control over register saving and restoring. 47extern "C" { 48#if defined(__arm__) 49 void ARMCompilationCallback(void); 50 asm( 51 ".text\n" 52 ".align 2\n" 53 ".globl " ASMPREFIX "ARMCompilationCallback\n" 54 ASMPREFIX "ARMCompilationCallback:\n" 55 // Save caller saved registers since they may contain stuff 56 // for the real target function right now. We have to act as if this 57 // whole compilation callback doesn't exist as far as the caller is 58 // concerned, so we can't just preserve the callee saved regs. 59 "stmdb sp!, {r0, r1, r2, r3, lr}\n" 60 // The LR contains the address of the stub function on entry. 61 // pass it as the argument to the C part of the callback 62 "mov r0, lr\n" 63 "sub sp, sp, #4\n" 64 // Call the C portion of the callback 65 "bl " ASMPREFIX "ARMCompilationCallbackC\n" 66 "add sp, sp, #4\n" 67 // Restoring the LR to the return address of the function that invoked 68 // the stub and de-allocating the stack space for it requires us to 69 // swap the two saved LR values on the stack, as they're backwards 70 // for what we need since the pop instruction has a pre-determined 71 // order for the registers. 72 // +--------+ 73 // 0 | LR | Original return address 74 // +--------+ 75 // 1 | LR | Stub address (start of stub) 76 // 2-5 | R3..R0 | Saved registers (we need to preserve all regs) 77 // +--------+ 78 // 79 // We need to exchange the values in slots 0 and 1 so we can 80 // return to the address in slot 1 with the address in slot 0 81 // restored to the LR. 82 "ldr r0, [sp,#20]\n" 83 "ldr r1, [sp,#16]\n" 84 "str r1, [sp,#20]\n" 85 "str r0, [sp,#16]\n" 86 // Return to the (newly modified) stub to invoke the real function. 87 // The above twiddling of the saved return addresses allows us to 88 // deallocate everything, including the LR the stub saved, all in one 89 // pop instruction. 90 "ldmia sp!, {r0, r1, r2, r3, lr, pc}\n" 91 ); 92#else // Not an ARM host 93 void ARMCompilationCallback() { 94 assert(0 && "Cannot call ARMCompilationCallback() on a non-ARM arch!\n"); 95 abort(); 96 } 97#endif 98} 99 100/// ARMCompilationCallbackC - This is the target-specific function invoked 101/// by the function stub when we did not know the real target of a call. 102/// This function must locate the start of the stub or call site and pass 103/// it into the JIT compiler function. 104extern "C" void ARMCompilationCallbackC(intptr_t StubAddr) { 105 // Get the address of the compiled code for this function. 106 intptr_t NewVal = (intptr_t)JITCompilerFunction((void*)StubAddr); 107 108 // Rewrite the call target... so that we don't end up here every time we 109 // execute the call. We're replacing the first two instructions of the 110 // stub with: 111 // ldr pc, [pc,#-4] 112 // <addr> 113 bool ok = sys::Memory::setRangeWritable ((void*)StubAddr, 8); 114 if (!ok) 115 { 116 cerr << "ERROR: Unable to mark stub writable\n"; 117 abort(); 118 } 119 *(intptr_t *)StubAddr = 0xe51ff004; 120 *(intptr_t *)(StubAddr+4) = NewVal; 121 ok = sys::Memory::setRangeExecutable ((void*)StubAddr, 8); 122 if (!ok) 123 { 124 cerr << "ERROR: Unable to mark stub executable\n"; 125 abort(); 126 } 127} 128 129TargetJITInfo::LazyResolverFn 130ARMJITInfo::getLazyResolverFunction(JITCompilerFn F) { 131 JITCompilerFunction = F; 132 return ARMCompilationCallback; 133} 134 135void *ARMJITInfo::emitFunctionStub(const Function* F, void *Fn, 136 MachineCodeEmitter &MCE) { 137 unsigned addr = (intptr_t)Fn; 138 // If this is just a call to an external function, emit a branch instead of a 139 // call. The code is the same except for one bit of the last instruction. 140 if (Fn != (void*)(intptr_t)ARMCompilationCallback) { 141 // branch to the corresponding function addr 142 // the stub is 8-byte size and 4-aligned 143 MCE.startFunctionStub(F, 8, 4); 144 MCE.emitWordLE(0xe51ff004); // LDR PC, [PC,#-4] 145 MCE.emitWordLE(addr); // addr of function 146 } else { 147 // The compilation callback will overwrite the first two words of this 148 // stub with indirect branch instructions targeting the compiled code. 149 // This stub sets the return address to restart the stub, so that 150 // the new branch will be invoked when we come back. 151 // 152 // branch and link to the compilation callback. 153 // the stub is 16-byte size and 4-byte aligned. 154 MCE.startFunctionStub(F, 16, 4); 155 // Save LR so the callback can determine which stub called it. 156 // The compilation callback is responsible for popping this prior 157 // to returning. 158 MCE.emitWordLE(0xe92d4000); // PUSH {lr} 159 // Set the return address to go back to the start of this stub 160 MCE.emitWordLE(0xe24fe00c); // SUB LR, PC, #12 161 // Invoke the compilation callback 162 MCE.emitWordLE(0xe51ff004); // LDR PC, [PC,#-4] 163 // The address of the compilation callback 164 MCE.emitWordLE((intptr_t)ARMCompilationCallback); 165 } 166 167 return MCE.finishFunctionStub(F); 168} 169 170/// relocate - Before the JIT can run a block of code that has been emitted, 171/// it must rewrite the code to contain the actual addresses of any 172/// referenced global symbols. 173void ARMJITInfo::relocate(void *Function, MachineRelocation *MR, 174 unsigned NumRelocs, unsigned char* GOTBase) { 175 for (unsigned i = 0; i != NumRelocs; ++i, ++MR) { 176 void *RelocPos = (char*)Function + MR->getMachineCodeOffset(); 177 intptr_t ResultPtr = (intptr_t)MR->getResultPointer(); 178 switch ((ARM::RelocationType)MR->getRelocationType()) { 179 case ARM::reloc_arm_relative: { 180 // It is necessary to calculate the correct PC relative value. We 181 // subtract the base addr from the target addr to form a byte offset. 182 ResultPtr = ResultPtr-(intptr_t)RelocPos-8; 183 // If the result is positive, set bit U(23) to 1. 184 if (ResultPtr >= 0) 185 *((unsigned*)RelocPos) |= 1 << 23; 186 else { 187 // otherwise, obtain the absolute value and set 188 // bit U(23) to 0. 189 ResultPtr *= -1; 190 *((unsigned*)RelocPos) &= 0xFF7FFFFF; 191 } 192 // set the immed value calculated 193 *((unsigned*)RelocPos) |= (unsigned)ResultPtr; 194 // set register Rn to PC 195 *((unsigned*)RelocPos) |= 0xF << 16; 196 break; 197 } 198 case ARM::reloc_arm_branch: { 199 // It is necessary to calculate the correct value of signed_immed_24 200 // field. We subtract the base addr from the target addr to form a 201 // byte offset, which must be inside the range -33554432 and +33554428. 202 // Then, we set the signed_immed_24 field of the instruction to bits 203 // [25:2] of the byte offset. More details ARM-ARM p. A4-11. 204 ResultPtr = ResultPtr-(intptr_t)RelocPos-8; 205 ResultPtr = (ResultPtr & 0x03FFFFFC) >> 2; 206 assert(ResultPtr >= -33554432 && ResultPtr <= 33554428); 207 *((unsigned*)RelocPos) |= ResultPtr; 208 break; 209 } 210 } 211 } 212} 213