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