1 //===-- ARMJITInfo.cpp - Implement the JIT interfaces for the ARM target --===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file implements the JIT interfaces for the ARM target.
12 //===----------------------------------------------------------------------===//
14 #define DEBUG_TYPE "jit"
15 #include "ARMJITInfo.h"
16 #include "ARMConstantPoolValue.h"
17 #include "ARMRelocations.h"
18 #include "ARMSubtarget.h"
19 #include "llvm/Function.h"
20 #include "llvm/CodeGen/MachineCodeEmitter.h"
21 #include "llvm/Config/alloca.h"
22 #include "llvm/Support/Streams.h"
23 #include "llvm/System/Memory.h"
27 void ARMJITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
31 /// JITCompilerFunction - This contains the address of the JIT function used to
32 /// compile a function lazily.
33 static TargetJITInfo::JITCompilerFn JITCompilerFunction;
35 // Get the ASMPREFIX for the current host. This is often '_'.
36 #ifndef __USER_LABEL_PREFIX__
37 #define __USER_LABEL_PREFIX__
39 #define GETASMPREFIX2(X) #X
40 #define GETASMPREFIX(X) GETASMPREFIX2(X)
41 #define ASMPREFIX GETASMPREFIX(__USER_LABEL_PREFIX__)
43 // CompilationCallback stub - We can't use a C function with inline assembly in
44 // it, because we the prolog/epilog inserted by GCC won't work for us (we need
45 // to preserve more context and manipulate the stack directly). Instead,
46 // write our own wrapper, which does things our way, so we have complete
47 // control over register saving and restoring.
50 void ARMCompilationCallback(void);
54 ".globl " ASMPREFIX "ARMCompilationCallback\n"
55 ASMPREFIX "ARMCompilationCallback:\n"
56 // Save caller saved registers since they may contain stuff
57 // for the real target function right now. We have to act as if this
58 // whole compilation callback doesn't exist as far as the caller is
59 // concerned, so we can't just preserve the callee saved regs.
60 "stmdb sp!, {r0, r1, r2, r3, lr}\n"
61 // The LR contains the address of the stub function on entry.
62 // pass it as the argument to the C part of the callback
65 // Call the C portion of the callback
66 "bl " ASMPREFIX "ARMCompilationCallbackC\n"
68 // Restoring the LR to the return address of the function that invoked
69 // the stub and de-allocating the stack space for it requires us to
70 // swap the two saved LR values on the stack, as they're backwards
71 // for what we need since the pop instruction has a pre-determined
72 // order for the registers.
74 // 0 | LR | Original return address
76 // 1 | LR | Stub address (start of stub)
77 // 2-5 | R3..R0 | Saved registers (we need to preserve all regs)
80 // We need to exchange the values in slots 0 and 1 so we can
81 // return to the address in slot 1 with the address in slot 0
82 // restored to the LR.
87 // Return to the (newly modified) stub to invoke the real function.
88 // The above twiddling of the saved return addresses allows us to
89 // deallocate everything, including the LR the stub saved, all in one
91 "ldmia sp!, {r0, r1, r2, r3, lr, pc}\n"
93 #else // Not an ARM host
94 void ARMCompilationCallback() {
95 assert(0 && "Cannot call ARMCompilationCallback() on a non-ARM arch!\n");
101 /// ARMCompilationCallbackC - This is the target-specific function invoked
102 /// by the function stub when we did not know the real target of a call.
103 /// This function must locate the start of the stub or call site and pass
104 /// it into the JIT compiler function.
105 extern "C" void ARMCompilationCallbackC(intptr_t StubAddr) {
106 // Get the address of the compiled code for this function.
107 intptr_t NewVal = (intptr_t)JITCompilerFunction((void*)StubAddr);
109 // Rewrite the call target... so that we don't end up here every time we
110 // execute the call. We're replacing the first two instructions of the
114 bool ok = sys::Memory::setRangeWritable((void*)StubAddr, 8);
117 cerr << "ERROR: Unable to mark stub writable\n";
120 *(intptr_t *)StubAddr = 0xe51ff004;
121 *(intptr_t *)(StubAddr+4) = NewVal;
122 ok = sys::Memory::setRangeExecutable((void*)StubAddr, 8);
125 cerr << "ERROR: Unable to mark stub executable\n";
130 TargetJITInfo::LazyResolverFn
131 ARMJITInfo::getLazyResolverFunction(JITCompilerFn F) {
132 JITCompilerFunction = F;
133 return ARMCompilationCallback;
136 void *ARMJITInfo::emitFunctionStub(const Function* F, void *Fn,
137 MachineCodeEmitter &MCE) {
138 unsigned addr = (intptr_t)Fn;
139 // If this is just a call to an external function, emit a branch instead of a
140 // call. The code is the same except for one bit of the last instruction.
141 if (Fn != (void*)(intptr_t)ARMCompilationCallback) {
142 // branch to the corresponding function addr
143 // the stub is 8-byte size and 4-aligned
144 MCE.startFunctionStub(F, 8, 4);
145 MCE.emitWordLE(0xe51ff004); // LDR PC, [PC,#-4]
146 MCE.emitWordLE(addr); // addr of function
148 // The compilation callback will overwrite the first two words of this
149 // stub with indirect branch instructions targeting the compiled code.
150 // This stub sets the return address to restart the stub, so that
151 // the new branch will be invoked when we come back.
153 // branch and link to the compilation callback.
154 // the stub is 16-byte size and 4-byte aligned.
155 MCE.startFunctionStub(F, 16, 4);
156 // Save LR so the callback can determine which stub called it.
157 // The compilation callback is responsible for popping this prior
159 MCE.emitWordLE(0xe92d4000); // PUSH {lr}
160 // Set the return address to go back to the start of this stub
161 MCE.emitWordLE(0xe24fe00c); // SUB LR, PC, #12
162 // Invoke the compilation callback
163 MCE.emitWordLE(0xe51ff004); // LDR PC, [PC,#-4]
164 // The address of the compilation callback
165 MCE.emitWordLE((intptr_t)ARMCompilationCallback);
168 return MCE.finishFunctionStub(F);
171 intptr_t ARMJITInfo::resolveRelocationAddr(MachineRelocation *MR) const {
172 ARM::RelocationType RT = (ARM::RelocationType)MR->getRelocationType();
173 if (RT == ARM::reloc_arm_cp_entry)
174 return getConstantPoolEntryAddr(MR->getConstantPoolIndex());
175 else if (RT == ARM::reloc_arm_machine_cp_entry) {
176 const MachineConstantPoolEntry &MCPE = (*MCPEs)[MR->getConstantVal()];
177 assert(MCPE.isMachineConstantPoolEntry() &&
178 "Expecting a machine constant pool entry!");
179 ARMConstantPoolValue *ACPV =
180 static_cast<ARMConstantPoolValue*>(MCPE.Val.MachineCPVal);
181 assert((!ACPV->hasModifier() && !ACPV->mustAddCurrentAddress()) &&
182 "Can't handle this machine constant pool entry yet!");
183 intptr_t Addr = (intptr_t)(MR->getResultPointer());
184 Addr -= getPCLabelAddr(ACPV->getLabelId()) + ACPV->getPCAdjustment();
187 return (intptr_t)(MR->getResultPointer());
190 /// relocate - Before the JIT can run a block of code that has been emitted,
191 /// it must rewrite the code to contain the actual addresses of any
192 /// referenced global symbols.
193 void ARMJITInfo::relocate(void *Function, MachineRelocation *MR,
194 unsigned NumRelocs, unsigned char* GOTBase) {
195 for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
196 void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
197 // If this is a constpool relocation, get the address of the
198 // constpool_entry instruction.
199 intptr_t ResultPtr = resolveRelocationAddr(MR);
200 switch ((ARM::RelocationType)MR->getRelocationType()) {
201 case ARM::reloc_arm_cp_entry:
202 case ARM::reloc_arm_relative: {
203 // It is necessary to calculate the correct PC relative value. We
204 // subtract the base addr from the target addr to form a byte offset.
205 ResultPtr = ResultPtr-(intptr_t)RelocPos-8;
206 // If the result is positive, set bit U(23) to 1.
208 *((unsigned*)RelocPos) |= 1 << 23;
210 // Otherwise, obtain the absolute value and set
213 *((unsigned*)RelocPos) &= 0xFF7FFFFF;
215 // Set the immed value calculated.
216 *((unsigned*)RelocPos) |= (unsigned)ResultPtr;
217 // Set register Rn to PC.
218 *((unsigned*)RelocPos) |= 0xF << 16;
221 case ARM::reloc_arm_machine_cp_entry:
222 case ARM::reloc_arm_absolute: {
223 // These addresses have already been resolved.
224 *((unsigned*)RelocPos) += (unsigned)ResultPtr;
227 case ARM::reloc_arm_branch: {
228 // It is necessary to calculate the correct value of signed_immed_24
229 // field. We subtract the base addr from the target addr to form a
230 // byte offset, which must be inside the range -33554432 and +33554428.
231 // Then, we set the signed_immed_24 field of the instruction to bits
232 // [25:2] of the byte offset. More details ARM-ARM p. A4-11.
233 ResultPtr = ResultPtr-(intptr_t)RelocPos-8;
234 ResultPtr = (ResultPtr & 0x03FFFFFC) >> 2;
235 assert(ResultPtr >= -33554432 && ResultPtr <= 33554428);
236 *((unsigned*)RelocPos) |= ResultPtr;