ARMJITInfo.cpp revision 2b483b5fb10fd3e6223b824726c9403bb47c1e1c 
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 <cstdlib>
22using namespace llvm;
23
24void ARMJITInfo::replaceMachineCodeForFunction(void *Old, void *New) {
25  abort();
26}
27
28/// JITCompilerFunction - This contains the address of the JIT function used to
29/// compile a function lazily.
30static TargetJITInfo::JITCompilerFn JITCompilerFunction;
31
32// CompilationCallback stub - We can't use a C function with inline assembly in
33// it, because we the prolog/epilog inserted by GCC won't work for us.  Instead,
34// write our own wrapper, which does things our way, so we have complete control
35// over register saving and restoring.
36extern "C" {
37#if defined(__arm__)
38  void ARMCompilationCallback(void);
39  asm(
40    ".text\n"
41    ".align 2\n"
42    ".globl ARMCompilationCallback\n"
43    "ARMCompilationCallback:\n"
44    // save main registers
45    "mov    ip, sp\n"
46    "stmfd  sp!, {fp, ip, lr, pc}\n"
47    "sub    fp, ip, #4\n"
48    // arguments to Compilation Callback
49    // r0 - our lr (address of the call instruction in stub plus 4)
50    // r1 - stub's lr (address of instruction that called the stub plus 4)
51    "mov    r0, fp\n"  // stub's frame
52    "mov    r1, lr\n"  // stub's lr
53    "bl     ARMCompilationCallbackC\n"
54    // restore main registers
55    "ldmfd  sp, {fp, sp, pc}\n");
56#else // Not an ARM host
57  void ARMCompilationCallback() {
58    assert(0 && "Cannot call ARMCompilationCallback() on a non-ARM arch!\n");
59    abort();
60  }
61#endif
62}
63
64/// ARMCompilationCallbackC - This is the target-specific function invoked by the
65/// function stub when we did not know the real target of a call.  This function
66/// must locate the start of the stub or call site and pass it into the JIT
67/// compiler function.
68extern "C" void ARMCompilationCallbackC(intptr_t *StackPtr, intptr_t RetAddr) {
69  intptr_t *RetAddrLoc = &StackPtr[-1];
70
71  assert(*RetAddrLoc == RetAddr &&
72         "Could not find return address on the stack!");
73#if 0
74  DOUT << "In callback! Addr=" << (void*)RetAddr
75       << " FP=" << (void*)StackPtr
76       << ": Resolving call to function: "
77       << TheVM->getFunctionReferencedName((void*)RetAddr) << "\n";
78#endif
79  intptr_t Addr = RetAddr - 4;
80
81  intptr_t NewVal = (intptr_t)JITCompilerFunction((void*)Addr);
82
83  // Rewrite the call target... so that we don't end up here every time we
84  // execute the call.
85  *(intptr_t *)Addr = NewVal;
86
87  // Change the return address to reexecute the branch and link instruction...
88  *RetAddrLoc -= 12;
89}
90
91TargetJITInfo::LazyResolverFn
92ARMJITInfo::getLazyResolverFunction(JITCompilerFn F) {
93  JITCompilerFunction = F;
94  return ARMCompilationCallback;
95}
96
97void *ARMJITInfo::emitFunctionStub(const Function* F, void *Fn,
98                                   MachineCodeEmitter &MCE) {
99  unsigned addr = (intptr_t)Fn;
100  // If this is just a call to an external function, emit a branch instead of a
101  // call.  The code is the same except for one bit of the last instruction.
102  if (Fn != (void*)(intptr_t)ARMCompilationCallback) {
103    // branch to the corresponding function addr
104    // the stub is 8-byte size and 4-aligned
105    MCE.startFunctionStub(F, 8, 4);
106    MCE.emitWordLE(0xE51FF004); // LDR PC, [PC,#-4]
107    MCE.emitWordLE(addr);       // addr of function
108  } else {
109    // branch and link to the corresponding function addr
110    // the stub is 20-byte size and 4-aligned
111    MCE.startFunctionStub(F, 20, 4);
112    MCE.emitWordLE(0xE92D4800); // STMFD SP!, [R11, LR]
113    MCE.emitWordLE(0xE28FE004); // ADD LR, PC, #4
114    MCE.emitWordLE(0xE51FF004); // LDR PC, [PC,#-4]
115    MCE.emitWordLE(addr);       // addr of function
116    MCE.emitWordLE(0xE8BD8800); // LDMFD SP!, [R11, PC]
117  }
118
119  return MCE.finishFunctionStub(F);
120}
121
122/// relocate - Before the JIT can run a block of code that has been emitted,
123/// it must rewrite the code to contain the actual addresses of any
124/// referenced global symbols.
125void ARMJITInfo::relocate(void *Function, MachineRelocation *MR,
126                          unsigned NumRelocs, unsigned char* GOTBase) {
127  for (unsigned i = 0; i != NumRelocs; ++i, ++MR) {
128    void *RelocPos = (char*)Function + MR->getMachineCodeOffset();
129    intptr_t ResultPtr = (intptr_t)MR->getResultPointer();
130    switch ((ARM::RelocationType)MR->getRelocationType()) {
131    case ARM::reloc_arm_relative: {
132      // It is necessary to calculate the correct PC relative value. We
133      // subtract the base addr from the target addr to form a byte offset.
134      ResultPtr = ResultPtr-(intptr_t)RelocPos-8;
135      // If the result is positive, set bit U(23) to 1.
136      if (ResultPtr >= 0)
137        *((unsigned*)RelocPos) |= 1 << 23;
138      else {
139      // otherwise, obtain the absolute value and set
140      // bit U(23) to 0.
141        ResultPtr *= -1;
142        *((unsigned*)RelocPos) &= 0xFF7FFFFF;
143      }
144      // set the immed value calculated
145      *((unsigned*)RelocPos) |= (unsigned)ResultPtr;
146      // set register Rn to PC
147      *((unsigned*)RelocPos) |= 0xF << 16;
148      break;
149    }
150    case ARM::reloc_arm_branch: {
151      // It is necessary to calculate the correct value of signed_immed_24
152      // field. We subtract the base addr from the target addr to form a
153      // byte offset, which must be inside the range -33554432 and +33554428.
154      // Then, we set the signed_immed_24 field of the instruction to bits
155      // [25:2] of the byte offset. More details ARM-ARM p. A4-11.
156      ResultPtr = ResultPtr-(intptr_t)RelocPos-8;
157      ResultPtr = (ResultPtr & 0x03FFFFFC) >> 2;
158      assert(ResultPtr >= -33554432 && ResultPtr <= 33554428);
159      *((unsigned*)RelocPos) |= ResultPtr;
160      break;
161    }
162    }
163  }
164}
165