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//===-- Callback.cpp - Trap handler for function resolution ---------------===//
//
// This file defines the handler which is invoked when a reference to a
// non-codegen'd function is found. This file defines target specific code
// which is used by the JIT.
//
//===----------------------------------------------------------------------===//
#include "VM.h"
#include "Support/Statistic.h"
#include "llvm/CodeGen/MachineCodeEmitter.h"
#include <iostream>
static VM *TheVM = 0;
// CompilationCallback - Invoked the first time that a call site is found,
// which causes lazy compilation of the target function.
//
void VM::CompilationCallback() {
#if defined(i386) || defined(__i386__) || defined(__x86__)
unsigned *StackPtr = (unsigned*)__builtin_frame_address(0);
unsigned RetAddr = (unsigned)__builtin_return_address(0);
assert(StackPtr[1] == RetAddr &&
"Could not find return address on the stack!");
bool isStub = ((unsigned char*)RetAddr)[0] == 0xCD; // Interrupt marker?
// The call instruction should have pushed the return value onto the stack...
RetAddr -= 4; // Backtrack to the reference itself...
DEBUG(std::cerr << "In callback! Addr=0x" << std::hex << RetAddr
<< " ESP=0x" << (unsigned)StackPtr << std::dec
<< ": Resolving call to function: "
<< TheVM->getFunctionReferencedName((void*)RetAddr) << "\n");
// Sanity check to make sure this really is a call instruction...
assert(((unsigned char*)RetAddr)[-1] == 0xE8 && "Not a call instr!");
unsigned NewVal = (unsigned)TheVM->resolveFunctionReference((void*)RetAddr);
// Rewrite the call target... so that we don't fault every time we execute
// the call.
*(unsigned*)RetAddr = NewVal-RetAddr-4;
if (isStub) {
// If this is a stub, rewrite the call into an unconditional branch
// instruction so that two return addresses are not pushed onto the stack
// when the requested function finally gets called. This also makes the
// 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
((unsigned char*)RetAddr)[-1] = 0xE9;
}
// Change the return address to reexecute the call instruction...
StackPtr[1] -= 5;
#else
abort();
#endif
}
/// emitStubForFunction - This virtual method is used by the JIT when it needs
/// to emit the address of a function for a function whose code has not yet
/// been generated. In order to do this, it generates a stub which jumps to
/// the lazy function compiler, which will eventually get fixed to call the
/// function directly.
///
void *VM::emitStubForFunction(const Function &F) {
#if defined(i386) || defined(__i386__) || defined(__x86__)
MCE->startFunctionStub(F, 6);
MCE->emitByte(0xE8); // Call with 32 bit pc-rel destination...
MCE->emitGlobalAddress((GlobalValue*)&F, true);
MCE->emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
return MCE->finishFunctionStub(F);
#else
abort();
#endif
}
void VM::registerCallback() {
TheVM = this;
}
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