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/* Copyright 2014 MultiMC Contributors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
// CAUTION:
// This file contains all manner of hackery and insanity.
// I will not be responsible for any loss of sanity due to reading this code.
// Here be dragons!
#include "WinBacktrace.h"
#include <windows.h>
#ifndef __i386__
#error WinBacktrace is only supported on x86 architectures.
#endif
// We need to do some crazy shit to walk through the stack.
// Windows unwinds the stack when an exception is thrown, so we
// need to examine the EXCEPTION_POINTERS's CONTEXT.
size_t getBacktrace(StackFrame *stack, size_t size, CONTEXT ctx)
{
// Written using information and a bit of pseudocode from
// http://www.eptacom.net/pubblicazioni/pub_eng/except.html
// This is probably one of the most horrifying things I've ever written.
// This tracks whether the current EBP is valid.
// When an invalid EBP is encountered, we stop walking the stack.
bool validEBP = true;
DWORD ebp = ctx.Ebp; // The current EBP (Extended Base Pointer)
DWORD eip = ctx.Eip;
int i;
for (i = 0; i < size; i++)
{
if (ebp & 3)
validEBP = false;
// FIXME: This function is obsolete, according to MSDN.
else if (IsBadReadPtr((void*) ebp, 8))
validEBP = false;
if (!validEBP) break;
// Find the caller.
// On the first iteration, the caller is whatever EIP points to.
// On successive iterations, the caller is the byte after EBP.
BYTE* caller = !i ? (BYTE*)eip : *((BYTE**) ebp + 1);
// The first ebp is the EBP from the CONTEXT.
// On successive iterations, the EBP is the DWORD that the previous EBP points to.
ebp = !i ? ebp : *(DWORD*)ebp;
// Find the caller's module.
// We'll use VirtualQuery to get information about the caller's address.
MEMORY_BASIC_INFORMATION mbi;
VirtualQuery(caller, &mbi, sizeof(mbi));
// We can get the instance handle from the allocation base.
HINSTANCE hInst = (HINSTANCE)mbi.AllocationBase;
// If the handle is 0, then the EBP is invalid.
if (hInst == 0) validEBP = false;
// Otherwise, dump info about the caller.
else stack[i].address = (void*)caller;
}
return i;
}
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