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//===-- Emitter.cpp - Write machine code to executable memory -------------===//
//
// This file defines a MachineCodeEmitter object that is used by Jello to write
// machine code to memory and remember where relocatable values lie.
//
//===----------------------------------------------------------------------===//
#include "VM.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/Function.h"
#include "Support/Statistic.h"
namespace {
Statistic<> NumBytes("jello", "Number of bytes of machine code compiled");
class Emitter : public MachineCodeEmitter {
VM &TheVM;
unsigned char *CurBlock;
unsigned char *CurByte;
std::vector<std::pair<BasicBlock*, unsigned *> > BBRefs;
std::map<BasicBlock*, unsigned> BBLocations;
public:
Emitter(VM &vm) : TheVM(vm) {}
virtual void startFunction(MachineFunction &F);
virtual void finishFunction(MachineFunction &F);
virtual void startBasicBlock(MachineBasicBlock &BB);
virtual void emitByte(unsigned char B);
virtual void emitPCRelativeDisp(Value *V);
virtual void emitGlobalAddress(GlobalValue *V);
};
}
MachineCodeEmitter *VM::createEmitter(VM &V) {
return new Emitter(V);
}
#define _POSIX_MAPPED_FILES
#include <unistd.h>
#include <sys/mman.h>
static void *getMemory() {
return mmap(0, 4096*2, PROT_READ|PROT_WRITE|PROT_EXEC,
MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
}
void Emitter::startFunction(MachineFunction &F) {
CurBlock = (unsigned char *)getMemory();
CurByte = CurBlock; // Start writing at the beginning of the fn.
TheVM.addGlobalMapping(F.getFunction(), CurBlock);
}
void Emitter::finishFunction(MachineFunction &F) {
for (unsigned i = 0, e = BBRefs.size(); i != e; ++i) {
unsigned Location = BBLocations[BBRefs[i].first];
unsigned *Ref = BBRefs[i].second;
*Ref = Location-(unsigned)Ref-4;
}
BBRefs.clear();
BBLocations.clear();
NumBytes += CurByte-CurBlock;
DEBUG(std::cerr << "Finished CodeGen of [" << std::hex << (unsigned)CurBlock
<< std::dec << "] Function: " << F.getFunction()->getName()
<< ": " << CurByte-CurBlock << " bytes of text\n");
}
void Emitter::startBasicBlock(MachineBasicBlock &BB) {
BBLocations[BB.getBasicBlock()] = (unsigned)CurByte;
}
void Emitter::emitByte(unsigned char B) {
*CurByte++ = B; // Write the byte to memory
}
// emitPCRelativeDisp - For functions, just output a displacement that will
// cause a reference to the zero page, which will cause a seg-fault, causing
// things to get resolved on demand. Keep track of these markers.
//
// For basic block references, keep track of where the references are so they
// may be patched up when the basic block is defined.
//
void Emitter::emitPCRelativeDisp(Value *V) {
if (Function *F = dyn_cast<Function>(V)) {
TheVM.addFunctionRef(CurByte, F);
unsigned ZeroAddr = -(unsigned)CurByte-4; // Calculate displacement to null
*(unsigned*)CurByte = ZeroAddr; // 4 byte offset
CurByte += 4;
} else {
BasicBlock *BB = cast<BasicBlock>(V); // Keep track of reference...
BBRefs.push_back(std::make_pair(BB, (unsigned*)CurByte));
CurByte += 4;
}
}
void Emitter::emitGlobalAddress(GlobalValue *V) {
*(void**)CurByte = TheVM.getPointerToGlobal(V);
CurByte += 4;
}
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