path: root/src/processor/stackwalker_amd64.cc

// Copyright (c) 2010 Google Inc.
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// stackwalker_amd64.cc: amd64-specific stackwalker.
//
// See stackwalker_amd64.h for documentation.
//
// Author: Mark Mentovai, Ted Mielczarek

#include <assert.h>

#include "common/scoped_ptr.h"
#include "google_breakpad/processor/call_stack.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 "google_breakpad/processor/system_info.h"
#include "processor/cfi_frame_info.h"
#include "processor/logging.h"
#include "processor/stackwalker_amd64.h"

namespace google_breakpad {


const StackwalkerAMD64::CFIWalker::RegisterSet
StackwalkerAMD64::cfi_register_map_[] = {
  // It may seem like $rip and $rsp are callee-saves, because 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 --- clearly wrong for $rip
  // and $rsp.
  { "$rax", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_RAX, &MDRawContextAMD64::rax },
  { "$rdx", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_RDX, &MDRawContextAMD64::rdx },
  { "$rcx", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_RCX, &MDRawContextAMD64::rcx },
  { "$rbx", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_RBX, &MDRawContextAMD64::rbx },
  { "$rsi", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_RSI, &MDRawContextAMD64::rsi },
  { "$rdi", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_RDI, &MDRawContextAMD64::rdi },
  { "$rbp", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_RBP, &MDRawContextAMD64::rbp },
  { "$rsp", ".cfa", false,
    StackFrameAMD64::CONTEXT_VALID_RSP, &MDRawContextAMD64::rsp },
  { "$r8", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_R8,  &MDRawContextAMD64::r8 },
  { "$r9", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_R9,  &MDRawContextAMD64::r9 },
  { "$r10", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_R10, &MDRawContextAMD64::r10 },
  { "$r11", NULL, false,
    StackFrameAMD64::CONTEXT_VALID_R11, &MDRawContextAMD64::r11 },
  { "$r12", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_R12, &MDRawContextAMD64::r12 },
  { "$r13", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_R13, &MDRawContextAMD64::r13 },
  { "$r14", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_R14, &MDRawContextAMD64::r14 },
  { "$r15", NULL, true,
    StackFrameAMD64::CONTEXT_VALID_R15, &MDRawContextAMD64::r15 },
  { "$rip", ".ra", false,
    StackFrameAMD64::CONTEXT_VALID_RIP, &MDRawContextAMD64::rip },
};

StackwalkerAMD64::StackwalkerAMD64(const SystemInfo* system_info,
                                   const MDRawContextAMD64* 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]))) {
}

uint64_t StackFrameAMD64::ReturnAddress() const {
  assert(context_validity & StackFrameAMD64::CONTEXT_VALID_RIP);
  return context.rip;
}

StackFrame* StackwalkerAMD64::GetContextFrame() {
  if (!context_) {
    BPLOG(ERROR) << "Can't get context frame without context";
    return NULL;
  }

  StackFrameAMD64* frame = new StackFrameAMD64();

  // 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 = StackFrameAMD64::CONTEXT_VALID_ALL;
  frame->trust = StackFrame::FRAME_TRUST_CONTEXT;
  frame->instruction = frame->context.rip;

  return frame;
}

StackFrameAMD64* StackwalkerAMD64::GetCallerByCFIFrameInfo(
    const vector<StackFrame*> &frames,
    CFIFrameInfo* cfi_frame_info) {
  StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());

  scoped_ptr<StackFrameAMD64> frame(new StackFrameAMD64());
  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 = (StackFrameAMD64::CONTEXT_VALID_RIP
                                 | StackFrameAMD64::CONTEXT_VALID_RSP);
  if ((frame->context_validity & essentials) != essentials)
    return NULL;

  frame->trust = StackFrame::FRAME_TRUST_CFI;
  return frame.release();
}

bool StackwalkerAMD64::IsEndOfStack(uint64_t caller_rip, uint64_t caller_rsp,
                                    uint64_t callee_rsp) {
  // Treat an instruction address of 0 as end-of-stack.
  if (caller_rip == 0) {
    return true;
  }

  // If the new stack pointer is at a lower address than the old, then
  // that's clearly incorrect. Treat this as end-of-stack to enforce
  // progress and avoid infinite loops.
  if (caller_rsp < callee_rsp) {
    return true;
  }

  return false;
}

// Returns true if `ptr` is not in x86-64 canonical form.
// https://en.wikipedia.org/wiki/X86-64#Virtual_address_space_details
static bool is_non_canonical(uint64_t ptr) {
  return ptr > 0x7FFFFFFFFFFF && ptr < 0xFFFF800000000000;
}

StackFrameAMD64* StackwalkerAMD64::GetCallerByFramePointerRecovery(
    const vector<StackFrame*>& frames) {
  StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
  uint64_t last_rsp = last_frame->context.rsp;
  uint64_t last_rbp = last_frame->context.rbp;

  // Assume the presence of a frame pointer. This is not mandated by the
  // AMD64 ABI, c.f. section 3.2.2 footnote 7, though it is typical for
  // compilers to still preserve the frame pointer and not treat %rbp as a
  // general purpose register.
  //
  // With this assumption, the CALL instruction pushes the return address
  // onto the stack and sets %rip to the procedure to enter. The procedure
  // then establishes the stack frame with a prologue that PUSHes the current
  // %rbp onto the stack, MOVes the current %rsp to %rbp, and then allocates
  // space for any local variables. Using this procedure linking information,
  // it is possible to locate frame information for the callee:
  //
  // %caller_rsp = *(%callee_rbp + 16)
  // %caller_rip = *(%callee_rbp + 8)
  // %caller_rbp = *(%callee_rbp)

  // If rbp is not 8-byte aligned it can't be a frame pointer.
  if (last_rbp % 8 != 0) {
    return NULL;
  }

  uint64_t caller_rip, caller_rbp;
  if (memory_->GetMemoryAtAddress(last_rbp + 8, &caller_rip) &&
      memory_->GetMemoryAtAddress(last_rbp, &caller_rbp)) {
    uint64_t caller_rsp = last_rbp + 16;

    // If the recovered rip is not a canonical address it can't be
    // the return address, so rbp must not have been a frame pointer.
    if (is_non_canonical(caller_rip)) {
      return NULL;
    }

    // Simple sanity check that the stack is growing downwards as expected.
    if (IsEndOfStack(caller_rip, caller_rsp, last_rsp) ||
        caller_rbp < last_rbp) {
      // Reached end-of-stack or stack is not growing downwards.
      return NULL;
    }

    // Sanity check that resulting rbp is still inside stack memory.
    uint64_t unused;
    if (!memory_->GetMemoryAtAddress(caller_rbp, &unused)) {
      return NULL;
    }

    StackFrameAMD64* frame = new StackFrameAMD64();
    frame->trust = StackFrame::FRAME_TRUST_FP;
    frame->context = last_frame->context;
    frame->context.rip = caller_rip;
    frame->context.rsp = caller_rsp;
    frame->context.rbp = caller_rbp;
    frame->context_validity = StackFrameAMD64::CONTEXT_VALID_RIP |
                              StackFrameAMD64::CONTEXT_VALID_RSP |
                              StackFrameAMD64::CONTEXT_VALID_RBP;
    return frame;
  }

  return NULL;
}

StackFrameAMD64* StackwalkerAMD64::GetCallerByStackScan(
    const vector<StackFrame*> &frames) {
  StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
  uint64_t last_rsp = last_frame->context.rsp;
  uint64_t caller_rip_address, caller_rip;

  if (!ScanForReturnAddress(last_rsp, &caller_rip_address, &caller_rip,
                            frames.size() == 1 /* is_context_frame */)) {
    // No plausible return address was found.
    return NULL;
  }

  // Create a new stack frame (ownership will be transferred to the caller)
  // and fill it in.
  StackFrameAMD64* frame = new StackFrameAMD64();

  frame->trust = StackFrame::FRAME_TRUST_SCAN;
  frame->context = last_frame->context;
  frame->context.rip = caller_rip;
  // The caller's %rsp is directly underneath the return address pushed by
  // the call.
  frame->context.rsp = caller_rip_address + 8;
  frame->context_validity = StackFrameAMD64::CONTEXT_VALID_RIP |
                            StackFrameAMD64::CONTEXT_VALID_RSP;

  // Other unwinders give up if they don't have an %rbp value, so see if we
  // can pass some plausible value on.
  if (last_frame->context_validity & StackFrameAMD64::CONTEXT_VALID_RBP) {
    // Functions typically push their caller's %rbp immediately upon entry,
    // and then set %rbp to point to that. So if the callee's %rbp is
    // pointing to the first word below the alleged return address, presume
    // that the caller's %rbp is saved there.
    if (caller_rip_address - 8 == last_frame->context.rbp) {
      uint64_t caller_rbp = 0;
      if (memory_->GetMemoryAtAddress(last_frame->context.rbp, &caller_rbp) &&
          caller_rbp > caller_rip_address) {
        frame->context.rbp = caller_rbp;
        frame->context_validity |= StackFrameAMD64::CONTEXT_VALID_RBP;
      }
    } else if (last_frame->context.rbp >= caller_rip_address + 8) {
      // If the callee's %rbp is plausible as a value for the caller's
      // %rbp, presume that the callee left it unchanged.
      frame->context.rbp = last_frame->context.rbp;
      frame->context_validity |= StackFrameAMD64::CONTEXT_VALID_RBP;
    }
  }

  return frame;
}

StackFrame* StackwalkerAMD64::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<StackFrame*> &frames = *stack->frames();
  StackFrameAMD64* last_frame = static_cast<StackFrameAMD64*>(frames.back());
  scoped_ptr<StackFrameAMD64> new_frame;

  // If we have DWARF CFI information, use it.
  scoped_ptr<CFIFrameInfo> cfi_frame_info(
      frame_symbolizer_->FindCFIFrameInfo(last_frame));
  if (cfi_frame_info.get())
    new_frame.reset(GetCallerByCFIFrameInfo(frames, cfi_frame_info.get()));

  // If CFI was not available or failed, try using frame pointer recovery.
  if (!new_frame.get()) {
    new_frame.reset(GetCallerByFramePointerRecovery(frames));
  }

  // If all else fails, fall back to stack scanning.
  if (stack_scan_allowed && !new_frame.get()) {
    new_frame.reset(GetCallerByStackScan(frames));
  }

  // If nothing worked, tell the caller.
  if (!new_frame.get())
    return NULL;

  if (system_info_->os_short == "nacl") {
    // Apply constraints from Native Client's x86-64 sandbox.  These
    // registers have the 4GB-aligned sandbox base address (from r15)
    // added to them, and only the bottom 32 bits are relevant for
    // stack walking.
    new_frame->context.rip = static_cast<uint32_t>(new_frame->context.rip);
    new_frame->context.rsp = static_cast<uint32_t>(new_frame->context.rsp);
    new_frame->context.rbp = static_cast<uint32_t>(new_frame->context.rbp);
  }

  if (IsEndOfStack(new_frame->context.rip, new_frame->context.rsp,
                   last_frame->context.rsp)) {
    // Reached end-of-stack.
    return NULL;
  }

  // new_frame->context.rip 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.rip - 1;

  return new_frame.release();
}

}  // namespace google_breakpad