// Copyright 2010 Google LLC // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google LLC nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. // stackwalker_x86.cc: x86-specific stackwalker. // // See stackwalker_x86.h for documentation. // // Author: Mark Mentovai #ifdef HAVE_CONFIG_H #include // Must come first #endif #include #include #include "common/scoped_ptr.h" #include "google_breakpad/processor/call_stack.h" #include "google_breakpad/processor/code_modules.h" #include "google_breakpad/processor/memory_region.h" #include "google_breakpad/processor/source_line_resolver_interface.h" #include "google_breakpad/processor/stack_frame_cpu.h" #include "processor/logging.h" #include "processor/postfix_evaluator-inl.h" #include "processor/stackwalker_x86.h" #include "processor/windows_frame_info.h" #include "processor/cfi_frame_info.h" namespace google_breakpad { // Max reasonable size for a single x86 frame is 128 KB. This value is used in // a heuristic for recovering of the EBP chain after a scan for return address. // This value is based on a stack frame size histogram built for a set of // popular third party libraries which suggests that 99.5% of all frames are // smaller than 128 KB. static const uint32_t kMaxReasonableGapBetweenFrames = 128 * 1024; const StackwalkerX86::CFIWalker::RegisterSet StackwalkerX86::cfi_register_map_[] = { // It may seem like $eip and $esp are callee-saves, because (with Unix or // cdecl calling conventions) the callee is responsible for having them // restored upon return. But the callee_saves flags here really means // that the walker should assume they're unchanged if the CFI doesn't // mention them, which is clearly wrong for $eip and $esp. { "$eip", ".ra", false, StackFrameX86::CONTEXT_VALID_EIP, &MDRawContextX86::eip }, { "$esp", ".cfa", false, StackFrameX86::CONTEXT_VALID_ESP, &MDRawContextX86::esp }, { "$ebp", NULL, true, StackFrameX86::CONTEXT_VALID_EBP, &MDRawContextX86::ebp }, { "$eax", NULL, false, StackFrameX86::CONTEXT_VALID_EAX, &MDRawContextX86::eax }, { "$ebx", NULL, true, StackFrameX86::CONTEXT_VALID_EBX, &MDRawContextX86::ebx }, { "$ecx", NULL, false, StackFrameX86::CONTEXT_VALID_ECX, &MDRawContextX86::ecx }, { "$edx", NULL, false, StackFrameX86::CONTEXT_VALID_EDX, &MDRawContextX86::edx }, { "$esi", NULL, true, StackFrameX86::CONTEXT_VALID_ESI, &MDRawContextX86::esi }, { "$edi", NULL, true, StackFrameX86::CONTEXT_VALID_EDI, &MDRawContextX86::edi }, }; StackwalkerX86::StackwalkerX86(const SystemInfo* system_info, const MDRawContextX86* context, MemoryRegion* memory, const CodeModules* modules, StackFrameSymbolizer* resolver_helper) : Stackwalker(system_info, memory, modules, resolver_helper), context_(context), cfi_walker_(cfi_register_map_, (sizeof(cfi_register_map_) / sizeof(cfi_register_map_[0]))) { if (memory_ && memory_->GetBase() + memory_->GetSize() - 1 > 0xffffffff) { // The x86 is a 32-bit CPU, the limits of the supplied stack are invalid. // Mark memory_ = NULL, which will cause stackwalking to fail. BPLOG(ERROR) << "Memory out of range for stackwalking: " << HexString(memory_->GetBase()) << "+" << HexString(memory_->GetSize()); memory_ = NULL; } } StackFrameX86::~StackFrameX86() { if (windows_frame_info) delete windows_frame_info; windows_frame_info = NULL; if (cfi_frame_info) delete cfi_frame_info; cfi_frame_info = NULL; } uint64_t StackFrameX86::ReturnAddress() const { assert(context_validity & StackFrameX86::CONTEXT_VALID_EIP); return context.eip; } StackFrame* StackwalkerX86::GetContextFrame() { if (!context_) { BPLOG(ERROR) << "Can't get context frame without context"; return NULL; } StackFrameX86* frame = new StackFrameX86(); // The instruction pointer is stored directly in a register, so pull it // straight out of the CPU context structure. frame->context = *context_; frame->context_validity = StackFrameX86::CONTEXT_VALID_ALL; frame->trust = StackFrame::FRAME_TRUST_CONTEXT; frame->instruction = frame->context.eip; return frame; } StackFrameX86* StackwalkerX86::GetCallerByWindowsFrameInfo( const vector& frames, WindowsFrameInfo* last_frame_info, bool stack_scan_allowed) { StackFrame::FrameTrust trust = StackFrame::FRAME_TRUST_NONE; // The last frame can never be inline. A sequence of inline frames always // finishes with a conventional frame. assert(frames.back()->trust != StackFrame::FRAME_TRUST_INLINE); StackFrameX86* last_frame = static_cast(frames.back()); // Save the stack walking info we found, in case we need it later to // find the callee of the frame we're constructing now. last_frame->windows_frame_info = last_frame_info; // This function only covers the full STACK WIN case. If // last_frame_info is VALID_PARAMETER_SIZE-only, then we should // assume the traditional frame format or use some other strategy. if (last_frame_info->valid != WindowsFrameInfo::VALID_ALL) return NULL; // This stackwalker sets each frame's %esp to its value immediately prior // to the CALL into the callee. This means that %esp points to the last // callee argument pushed onto the stack, which may not be where %esp points // after the callee returns. Specifically, the value is correct for the // cdecl calling convention, but not other conventions. The cdecl // convention requires a caller to pop its callee's arguments from the // stack after the callee returns. This is usually accomplished by adding // the known size of the arguments to %esp. Other calling conventions, // including stdcall, thiscall, and fastcall, require the callee to pop any // parameters stored on the stack before returning. This is usually // accomplished by using the RET n instruction, which pops n bytes off // the stack after popping the return address. // // Because each frame's %esp will point to a location on the stack after // callee arguments have been PUSHed, when locating things in a stack frame // relative to %esp, the size of the arguments to the callee need to be // taken into account. This seems a little bit unclean, but it's better // than the alternative, which would need to take these same things into // account, but only for cdecl functions. With this implementation, we get // to be agnostic about each function's calling convention. Furthermore, // this is how Windows debugging tools work, so it means that the %esp // values produced by this stackwalker directly correspond to the %esp // values you'll see there. // // If the last frame has no callee (because it's the context frame), just // set the callee parameter size to 0: the stack pointer can't point to // callee arguments because there's no callee. This is correct as long // as the context wasn't captured while arguments were being pushed for // a function call. Note that there may be functions whose parameter sizes // are unknown, 0 is also used in that case. When that happens, it should // be possible to walk to the next frame without reference to %esp. uint32_t last_frame_callee_parameter_size = 0; int frames_already_walked = frames.size(); for (int last_frame_callee_id = frames_already_walked - 2; last_frame_callee_id >= 0; last_frame_callee_id--) { // Searching for a real callee frame. Skipping inline frames since they // cannot be downcasted to StackFrameX86. if (frames[last_frame_callee_id]->trust == StackFrame::FRAME_TRUST_INLINE) { continue; } const StackFrameX86* last_frame_callee = static_cast(frames[last_frame_callee_id]); WindowsFrameInfo* last_frame_callee_info = last_frame_callee->windows_frame_info; if (last_frame_callee_info && (last_frame_callee_info->valid & WindowsFrameInfo::VALID_PARAMETER_SIZE)) { last_frame_callee_parameter_size = last_frame_callee_info->parameter_size; } } // Set up the dictionary for the PostfixEvaluator. %ebp, %esp, and sometimes // %ebx are used in program strings, and their previous values are known, so // set them here. PostfixEvaluator::DictionaryType dictionary; // Provide the current register values. dictionary["$ebp"] = last_frame->context.ebp; dictionary["$esp"] = last_frame->context.esp; if (last_frame->context_validity & StackFrameX86::CONTEXT_VALID_EBX) dictionary["$ebx"] = last_frame->context.ebx; // Provide constants from the debug info for last_frame and its callee. // .cbCalleeParams is a Breakpad extension that allows us to use the // PostfixEvaluator engine when certain types of debugging information // are present without having to write the constants into the program // string as literals. dictionary[".cbCalleeParams"] = last_frame_callee_parameter_size; dictionary[".cbSavedRegs"] = last_frame_info->saved_register_size; dictionary[".cbLocals"] = last_frame_info->local_size; uint32_t raSearchStart = last_frame->context.esp + last_frame_callee_parameter_size + last_frame_info->local_size + last_frame_info->saved_register_size; uint32_t raSearchStartOld = raSearchStart; uint32_t found = 0; // dummy value // Scan up to three words above the calculated search value, in case // the stack was aligned to a quadword boundary. // // TODO(ivan.penkov): Consider cleaning up the scan for return address that // follows. The purpose of this scan is to adjust the .raSearchStart // calculation (which is based on register %esp) in the cases where register // %esp may have been aligned (up to a quadword). There are two problems // with this approach: // 1) In practice, 64 byte boundary alignment is seen which clearly can not // be handled by a three word scan. // 2) A search for a return address is "guesswork" by definition because // the results will be different depending on what is left on the stack // from previous executions. // So, basically, the results from this scan should be ignored if other means // for calculation of the value of .raSearchStart are available. if (ScanForReturnAddress(raSearchStart, &raSearchStart, &found, 3) && last_frame->trust == StackFrame::FRAME_TRUST_CONTEXT && last_frame->windows_frame_info != NULL && last_frame_info->type_ == WindowsFrameInfo::STACK_INFO_FPO && raSearchStartOld == raSearchStart && found == last_frame->context.eip) { // The context frame represents an FPO-optimized Windows system call. // On the top of the stack we have a pointer to the current instruction. // This means that the callee has returned but the return address is still // on the top of the stack which is very atypical situaltion. // Skip one slot from the stack and do another scan in order to get the // actual return address. raSearchStart += 4; ScanForReturnAddress(raSearchStart, &raSearchStart, &found, 3); } dictionary[".cbParams"] = last_frame_info->parameter_size; // Decide what type of program string to use. The program string is in // postfix notation and will be passed to PostfixEvaluator::Evaluate. // Given the dictionary and the program string, it is possible to compute // the return address and the values of other registers in the calling // function. Because of bugs described below, the stack may need to be // scanned for these values. The results of program string evaluation // will be used to determine whether to scan for better values. string program_string; bool recover_ebp = true; trust = StackFrame::FRAME_TRUST_CFI; if (!last_frame_info->program_string.empty()) { // The FPO data has its own program string, which will tell us how to // get to the caller frame, and may even fill in the values of // nonvolatile registers and provide pointers to local variables and // parameters. In some cases, particularly with program strings that use // .raSearchStart, the stack may need to be scanned afterward. program_string = last_frame_info->program_string; } else if (last_frame_info->allocates_base_pointer) { // The function corresponding to the last frame doesn't use the frame // pointer for conventional purposes, but it does allocate a new // frame pointer and use it for its own purposes. Its callee's // information is still accessed relative to %esp, and the previous // value of %ebp can be recovered from a location in its stack frame, // within the saved-register area. // // Functions that fall into this category use the %ebp register for // a purpose other than the frame pointer. They restore the caller's // %ebp before returning. These functions create their stack frame // after a CALL by decrementing the stack pointer in an amount // sufficient to store local variables, and then PUSHing saved // registers onto the stack. Arguments to a callee function, if any, // are PUSHed after that. Walking up to the caller, therefore, // can be done solely with calculations relative to the stack pointer // (%esp). The return address is recovered from the memory location // above the known sizes of the callee's parameters, saved registers, // and locals. The caller's stack pointer (the value of %esp when // the caller executed CALL) is the location immediately above the // saved return address. The saved value of %ebp to be restored for // the caller is at a known location in the saved-register area of // the stack frame. // // For this type of frame, MSVC 14 (from Visual Studio 8/2005) in // link-time code generation mode (/LTCG and /GL) can generate erroneous // debugging data. The reported size of saved registers can be 0, // which is clearly an error because these frames must, at the very // least, save %ebp. For this reason, in addition to those given above // about the use of .raSearchStart, the stack may need to be scanned // for a better return address and a better frame pointer after the // program string is evaluated. // // %eip_new = *(%esp_old + callee_params + saved_regs + locals) // %ebp_new = *(%esp_old + callee_params + saved_regs - 8) // %esp_new = %esp_old + callee_params + saved_regs + locals + 4 program_string = "$eip .raSearchStart ^ = " "$ebp $esp .cbCalleeParams + .cbSavedRegs + 8 - ^ = " "$esp .raSearchStart 4 + ="; } else { // The function corresponding to the last frame doesn't use %ebp at // all. The callee frame is located relative to %esp. // // The called procedure's instruction pointer and stack pointer are // recovered in the same way as the case above, except that no // frame pointer (%ebp) is used at all, so it is not saved anywhere // in the callee's stack frame and does not need to be recovered. // Because %ebp wasn't used in the callee, whatever value it has // is the value that it had in the caller, so it can be carried // straight through without bringing its validity into question. // // Because of the use of .raSearchStart, the stack will possibly be // examined to locate a better return address after program string // evaluation. The stack will not be examined to locate a saved // %ebp value, because these frames do not save (or use) %ebp. // // We also propagate %ebx through, as it is commonly unmodifed after // calling simple forwarding functions in ntdll (that are this non-EBP // using type). It's not clear that this is always correct, but it is // important for some functions to get a correct walk. // // %eip_new = *(%esp_old + callee_params + saved_regs + locals) // %esp_new = %esp_old + callee_params + saved_regs + locals + 4 // %ebp_new = %ebp_old // %ebx_new = %ebx_old // If available. program_string = "$eip .raSearchStart ^ = " "$esp .raSearchStart 4 + ="; if (last_frame->context_validity & StackFrameX86::CONTEXT_VALID_EBX) program_string += " $ebx $ebx ="; recover_ebp = false; } // Check for alignment operators in the program string. If alignment // operators are found, then current %ebp must be valid and it is the only // reliable data point that can be used for getting to the previous frame. // E.g. the .raSearchStart calculation (above) is based on %esp and since // %esp was aligned in the current frame (which is a lossy operation) the // calculated value of .raSearchStart cannot be correct and should not be // used. Instead .raSearchStart must be calculated based on %ebp. // The code that follows assumes that .raSearchStart is supposed to point // at the saved return address (ebp + 4). // For some more details on this topic, take a look at the following thread: // https://groups.google.com/forum/#!topic/google-breakpad-dev/ZP1FA9B1JjM if ((StackFrameX86::CONTEXT_VALID_EBP & last_frame->context_validity) != 0 && program_string.find('@') != string::npos) { raSearchStart = last_frame->context.ebp + 4; } // The difference between raSearch and raSearchStart is unknown, // but making them the same seems to work well in practice. dictionary[".raSearchStart"] = raSearchStart; dictionary[".raSearch"] = raSearchStart; // Now crank it out, making sure that the program string set at least the // two required variables. PostfixEvaluator evaluator = PostfixEvaluator(&dictionary, memory_); PostfixEvaluator::DictionaryValidityType dictionary_validity; if (!evaluator.Evaluate(program_string, &dictionary_validity) || dictionary_validity.find("$eip") == dictionary_validity.end() || dictionary_validity.find("$esp") == dictionary_validity.end()) { // Program string evaluation failed. It may be that %eip is not somewhere // with stack frame info, and %ebp is pointing to non-stack memory, so // our evaluation couldn't succeed. We'll scan the stack for a return // address. This can happen if the stack is in a module for which // we don't have symbols, and that module is compiled without a // frame pointer. uint32_t location_start = last_frame->context.esp; uint32_t location, eip; if (!stack_scan_allowed || !ScanForReturnAddress(location_start, &location, &eip, /*is_context_frame=*/last_frame->trust == StackFrame::FRAME_TRUST_CONTEXT)) { // if we can't find an instruction pointer even with stack scanning, // give up. return NULL; } // This seems like a reasonable return address. Since program string // evaluation failed, use it and set %esp to the location above the // one where the return address was found. dictionary["$eip"] = eip; dictionary["$esp"] = location + 4; trust = StackFrame::FRAME_TRUST_SCAN; } // Since this stack frame did not use %ebp in a traditional way, // locating the return address isn't entirely deterministic. In that // case, the stack can be scanned to locate the return address. // // However, if program string evaluation resulted in both %eip and // %ebp values of 0, trust that the end of the stack has been // reached and don't scan for anything else. if (dictionary["$eip"] != 0 || dictionary["$ebp"] != 0) { int offset = 0; // This scan can only be done if a CodeModules object is available, to // check that candidate return addresses are in fact inside a module. // // TODO(mmentovai): This ignores dynamically-generated code. One possible // solution is to check the minidump's memory map to see if the candidate // %eip value comes from a mapped executable page, although this would // require dumps that contain MINIDUMP_MEMORY_INFO, which the Breakpad // client doesn't currently write (it would need to call MiniDumpWriteDump // with the MiniDumpWithFullMemoryInfo type bit set). Even given this // ability, older OSes (pre-XP SP2) and CPUs (pre-P4) don't enforce // an independent execute privilege on memory pages. uint32_t eip = dictionary["$eip"]; if (modules_ && !modules_->GetModuleForAddress(eip)) { // The instruction pointer at .raSearchStart was invalid, so start // looking one 32-bit word above that location. uint32_t location_start = dictionary[".raSearchStart"] + 4; uint32_t location; if (stack_scan_allowed && ScanForReturnAddress(location_start, &location, &eip, /*is_context_frame=*/last_frame->trust == StackFrame::FRAME_TRUST_CONTEXT)) { // This is a better return address that what program string // evaluation found. Use it, and set %esp to the location above the // one where the return address was found. dictionary["$eip"] = eip; dictionary["$esp"] = location + 4; offset = location - location_start; trust = StackFrame::FRAME_TRUST_CFI_SCAN; } } if (recover_ebp) { // When trying to recover the previous value of the frame pointer (%ebp), // start looking at the lowest possible address in the saved-register // area, and look at the entire saved register area, increased by the // size of |offset| to account for additional data that may be on the // stack. The scan is performed from the highest possible address to // the lowest, because the expectation is that the function's prolog // would have saved %ebp early. uint32_t ebp = dictionary["$ebp"]; // When a scan for return address is used, it is possible to skip one or // more frames (when return address is not in a known module). One // indication for skipped frames is when the value of %ebp is lower than // the location of the return address on the stack bool has_skipped_frames = (trust != StackFrame::FRAME_TRUST_CFI && ebp <= raSearchStart + offset); uint32_t value; // throwaway variable to check pointer validity if (has_skipped_frames || !memory_->GetMemoryAtAddress(ebp, &value)) { int fp_search_bytes = last_frame_info->saved_register_size + offset; uint32_t location_end = last_frame->context.esp + last_frame_callee_parameter_size; for (uint32_t location = location_end + fp_search_bytes; location >= location_end; location -= 4) { if (!memory_->GetMemoryAtAddress(location, &ebp)) break; if (memory_->GetMemoryAtAddress(ebp, &value)) { // The candidate value is a pointer to the same memory region // (the stack). Prefer it as a recovered %ebp result. dictionary["$ebp"] = ebp; break; } } } } } // Create a new stack frame (ownership will be transferred to the caller) // and fill it in. StackFrameX86* frame = new StackFrameX86(); frame->trust = trust; frame->context = last_frame->context; frame->context.eip = dictionary["$eip"]; frame->context.esp = dictionary["$esp"]; frame->context.ebp = dictionary["$ebp"]; frame->context_validity = StackFrameX86::CONTEXT_VALID_EIP | StackFrameX86::CONTEXT_VALID_ESP | StackFrameX86::CONTEXT_VALID_EBP; // These are nonvolatile (callee-save) registers, and the program string // may have filled them in. if (dictionary_validity.find("$ebx") != dictionary_validity.end()) { frame->context.ebx = dictionary["$ebx"]; frame->context_validity |= StackFrameX86::CONTEXT_VALID_EBX; } if (dictionary_validity.find("$esi") != dictionary_validity.end()) { frame->context.esi = dictionary["$esi"]; frame->context_validity |= StackFrameX86::CONTEXT_VALID_ESI; } if (dictionary_validity.find("$edi") != dictionary_validity.end()) { frame->context.edi = dictionary["$edi"]; frame->context_validity |= StackFrameX86::CONTEXT_VALID_EDI; } return frame; } StackFrameX86* StackwalkerX86::GetCallerByCFIFrameInfo( const vector& frames, CFIFrameInfo* cfi_frame_info) { // The last frame can never be inline. A sequence of inline frames always // finishes with a conventional frame. assert(frames.back()->trust != StackFrame::FRAME_TRUST_INLINE); StackFrameX86* last_frame = static_cast(frames.back()); last_frame->cfi_frame_info = cfi_frame_info; scoped_ptr frame(new StackFrameX86()); if (!cfi_walker_ .FindCallerRegisters(*memory_, *cfi_frame_info, last_frame->context, last_frame->context_validity, &frame->context, &frame->context_validity)) return NULL; // Make sure we recovered all the essentials. static const int essentials = (StackFrameX86::CONTEXT_VALID_EIP | StackFrameX86::CONTEXT_VALID_ESP | StackFrameX86::CONTEXT_VALID_EBP); if ((frame->context_validity & essentials) != essentials) return NULL; frame->trust = StackFrame::FRAME_TRUST_CFI; return frame.release(); } StackFrameX86* StackwalkerX86::GetCallerByEBPAtBase( const vector& frames, bool stack_scan_allowed) { StackFrame::FrameTrust trust; // The last frame can never be inline. A sequence of inline frames always // finishes with a conventional frame. assert(frames.back()->trust != StackFrame::FRAME_TRUST_INLINE); StackFrameX86* last_frame = static_cast(frames.back()); uint32_t last_esp = last_frame->context.esp; uint32_t last_ebp = last_frame->context.ebp; // Assume that the standard %ebp-using x86 calling convention is in // use. // // The typical x86 calling convention, when frame pointers are present, // is for the calling procedure to use CALL, which pushes the return // address onto the stack and sets the instruction pointer (%eip) to // the entry point of the called routine. The called routine then // PUSHes the calling routine's frame pointer (%ebp) onto the stack // before copying the stack pointer (%esp) to the frame pointer (%ebp). // Therefore, the calling procedure's frame pointer is always available // by dereferencing the called procedure's frame pointer, and the return // address is always available at the memory location immediately above // the address pointed to by the called procedure's frame pointer. The // calling procedure's stack pointer (%esp) is 8 higher than the value // of the called procedure's frame pointer at the time the calling // procedure made the CALL: 4 bytes for the return address pushed by the // CALL itself, and 4 bytes for the callee's PUSH of the caller's frame // pointer. // // %eip_new = *(%ebp_old + 4) // %esp_new = %ebp_old + 8 // %ebp_new = *(%ebp_old) uint32_t caller_eip, caller_esp, caller_ebp; if (memory_->GetMemoryAtAddress(last_ebp + 4, &caller_eip) && memory_->GetMemoryAtAddress(last_ebp, &caller_ebp)) { caller_esp = last_ebp + 8; trust = StackFrame::FRAME_TRUST_FP; } else { // We couldn't read the memory %ebp refers to. It may be that %ebp // is pointing to non-stack memory. We'll scan the stack for a // return address. This can happen if last_frame is executing code // for a module for which we don't have symbols, and that module // is compiled without a frame pointer. if (!stack_scan_allowed || !ScanForReturnAddress(last_esp, &caller_esp, &caller_eip, /*is_context_frame=*/last_frame->trust == StackFrame::FRAME_TRUST_CONTEXT)) { // if we can't find an instruction pointer even with stack scanning, // give up. return NULL; } // ScanForReturnAddress found a reasonable return address. Advance %esp to // the location immediately above the one where the return address was // found. caller_esp += 4; // Try to restore the %ebp chain. The caller %ebp should be stored at a // location immediately below the one where the return address was found. // A valid caller %ebp must be greater than the address where it is stored // and the gap between the two adjacent frames should be reasonable. uint32_t restored_ebp_chain = caller_esp - 8; if (!memory_->GetMemoryAtAddress(restored_ebp_chain, &caller_ebp) || caller_ebp <= restored_ebp_chain || caller_ebp - restored_ebp_chain > kMaxReasonableGapBetweenFrames) { // The restored %ebp chain doesn't appear to be valid. // Assume that %ebp is unchanged. caller_ebp = last_ebp; } trust = StackFrame::FRAME_TRUST_SCAN; } // Create a new stack frame (ownership will be transferred to the caller) // and fill it in. StackFrameX86* frame = new StackFrameX86(); frame->trust = trust; frame->context = last_frame->context; frame->context.eip = caller_eip; frame->context.esp = caller_esp; frame->context.ebp = caller_ebp; frame->context_validity = StackFrameX86::CONTEXT_VALID_EIP | StackFrameX86::CONTEXT_VALID_ESP | StackFrameX86::CONTEXT_VALID_EBP; return frame; } StackFrame* StackwalkerX86::GetCallerFrame(const CallStack* stack, bool stack_scan_allowed) { if (!memory_ || !stack) { BPLOG(ERROR) << "Can't get caller frame without memory or stack"; return NULL; } const vector& frames = *stack->frames(); StackFrameX86* last_frame = static_cast(frames.back()); // The last frame can never be inline. A sequence of inline frames always // finishes with a conventional frame. assert(last_frame->trust != StackFrame::FRAME_TRUST_INLINE); scoped_ptr new_frame; // If the resolver has Windows stack walking information, use that. WindowsFrameInfo* windows_frame_info = frame_symbolizer_->FindWindowsFrameInfo(last_frame); if (windows_frame_info) new_frame.reset(GetCallerByWindowsFrameInfo(frames, windows_frame_info, stack_scan_allowed)); // If the resolver has DWARF CFI information, use that. if (!new_frame.get()) { CFIFrameInfo* cfi_frame_info = frame_symbolizer_->FindCFIFrameInfo(last_frame); if (cfi_frame_info) new_frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info)); } // Otherwise, hope that the program was using a traditional frame structure. if (!new_frame.get()) new_frame.reset(GetCallerByEBPAtBase(frames, stack_scan_allowed)); // If nothing worked, tell the caller. if (!new_frame.get()) return NULL; // Should we terminate the stack walk? (end-of-stack or broken invariant) if (TerminateWalk(new_frame->context.eip, new_frame->context.esp, last_frame->context.esp, /*first_unwind=*/last_frame->trust == StackFrame::FRAME_TRUST_CONTEXT)) { return NULL; } // new_frame->context.eip is the return address, which is the instruction // after the CALL that caused us to arrive at the callee. Set // new_frame->instruction to one less than that, so it points within the // CALL instruction. See StackFrame::instruction for details, and // StackFrameAMD64::ReturnAddress. new_frame->instruction = new_frame->context.eip - 1; return new_frame.release(); } } // namespace google_breakpad