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//===-- Callback.cpp - Trap handler for function resolution ---------------===//
//
// This file defines the SIGSEGV handler which is invoked when a reference to a
// non-codegen'd function is found.
//
//===----------------------------------------------------------------------===//
#include "VM.h"
#include <signal.h>
#include <ucontext.h>
#include <iostream>
static VM *TheVM = 0;
static void TrapHandler(int TN, siginfo_t *SI, ucontext_t *ucp) {
assert(TN == SIGSEGV && "Should be SIGSEGV!");
if (SI->si_code != SEGV_MAPERR || SI->si_addr != 0 ||
ucp->uc_mcontext.gregs[REG_EIP] != 0) {
std::cerr << "Bad SEGV encountered!\n";
abort();
}
// The call instruction should have pushed the return value onto the stack...
unsigned RefAddr = *(unsigned*)ucp->uc_mcontext.gregs[REG_ESP];
RefAddr -= 4; // Backtrack to the reference itself...
std::cerr << "In SEGV handler! Addr=0x" << std::hex << RefAddr
<< " ESP=0x" << ucp->uc_mcontext.gregs[REG_ESP] << std::dec
<< ": Resolving call to function: "
<< TheVM->getFunctionReferencedName((void*)RefAddr) << "\n";
// Sanity check to make sure this really is a call instruction...
assert(((unsigned char*)RefAddr)[-1] == 0xE8 && "Not a call instr!");
unsigned NewVal = (unsigned)TheVM->resolveFunctionReference((void*)RefAddr);
// Rewrite the call target... so that we don't fault every time we execute
// the call.
*(unsigned*)RefAddr = NewVal-RefAddr-4;
// Change the instruction pointer to be the real target of the call...
ucp->uc_mcontext.gregs[REG_EIP] = NewVal;
}
void VM::registerCallback() {
TheVM = this;
// Register the signal handler...
struct sigaction SA;
SA.sa_sigaction = (void (*)(int, siginfo_t*, void*))TrapHandler;
sigfillset(&SA.sa_mask); // Block all signals while codegen'ing
SA.sa_flags = SA_NOCLDSTOP|SA_SIGINFO; // Get siginfo
sigaction(SIGSEGV, &SA, 0); // Install the handler
}
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