blob: 1e07e042b0a50fb9a720a7e853866d29b3cd9991 [file] [log] [blame]
// Generate stack tracer for aarch64
#if defined(__linux__)
#include <signal.h>
#include <sys/mman.h>
#include <ucontext.h>
#include <unistd.h>
#include <atomic>
#include <cassert>
#include <cstdint>
#include <iostream>
#include <limits>
#include "absl/base/attributes.h"
#include "absl/debugging/internal/address_is_readable.h"
#include "absl/debugging/internal/vdso_support.h" // a no-op on non-elf or non-glibc systems
#include "absl/debugging/stacktrace.h"
static const size_t kUnknownFrameSize = 0;
// Stack end to use when we don't know the actual stack end
// (effectively just the end of address space).
constexpr uintptr_t kUnknownStackEnd =
std::numeric_limits<size_t>::max() - sizeof(void *);
#if defined(__linux__)
// Returns the address of the VDSO __kernel_rt_sigreturn function, if present.
static const unsigned char* GetKernelRtSigreturnAddress() {
constexpr uintptr_t kImpossibleAddress = 1;
ABSL_CONST_INIT static std::atomic<uintptr_t> memoized{kImpossibleAddress};
uintptr_t address = memoized.load(std::memory_order_relaxed);
if (address != kImpossibleAddress) {
return reinterpret_cast<const unsigned char*>(address);
address = reinterpret_cast<uintptr_t>(nullptr);
absl::debugging_internal::VDSOSupport vdso;
if (vdso.IsPresent()) {
absl::debugging_internal::VDSOSupport::SymbolInfo symbol_info;
auto lookup = [&](int type) {
return vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_2.6.39", type,
if ((!lookup(STT_FUNC) && !lookup(STT_NOTYPE)) ||
symbol_info.address == nullptr) {
// Unexpected: VDSO is present, yet the expected symbol is missing
// or null.
assert(false && "VDSO is present, but doesn't have expected symbol");
} else {
if (reinterpret_cast<uintptr_t>(symbol_info.address) !=
kImpossibleAddress) {
address = reinterpret_cast<uintptr_t>(symbol_info.address);
} else {
assert(false && "VDSO returned invalid address");
#endif, std::memory_order_relaxed);
return reinterpret_cast<const unsigned char*>(address);
#endif // __linux__
// Compute the size of a stack frame in [low..high). We assume that
// low < high. Return size of kUnknownFrameSize.
template<typename T>
static size_t ComputeStackFrameSize(const T* low,
const T* high) {
const char* low_char_ptr = reinterpret_cast<const char *>(low);
const char* high_char_ptr = reinterpret_cast<const char *>(high);
return low < high ? static_cast<size_t>(high_char_ptr - low_char_ptr)
: kUnknownFrameSize;
// Saves stack info that is expensive to calculate to avoid recalculating per frame.
struct StackInfo {
uintptr_t stack_low;
uintptr_t stack_high;
uintptr_t sig_stack_low;
uintptr_t sig_stack_high;
static bool InsideSignalStack(void** ptr, const StackInfo* stack_info) {
uintptr_t comparable_ptr = reinterpret_cast<uintptr_t>(ptr);
return (comparable_ptr >= stack_info->sig_stack_low &&
comparable_ptr < stack_info->sig_stack_high);
// Given a pointer to a stack frame, locate and return the calling
// stackframe, or return null if no stackframe can be found. Perform sanity
// checks (the strictness of which is controlled by the boolean parameter
// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack.
ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack.
static void **NextStackFrame(void **old_frame_pointer, const void *uc,
const StackInfo *stack_info) {
void **new_frame_pointer = reinterpret_cast<void**>(*old_frame_pointer);
#if defined(__linux__)
if (WITH_CONTEXT && uc != nullptr) {
// Check to see if next frame's return address is __kernel_rt_sigreturn.
if (old_frame_pointer[1] == GetKernelRtSigreturnAddress()) {
const ucontext_t *ucv = static_cast<const ucontext_t *>(uc);
// old_frame_pointer[0] is not suitable for unwinding, look at
// ucontext to discover frame pointer before signal.
void **const pre_signal_frame_pointer =
reinterpret_cast<void **>(ucv->uc_mcontext.regs[29]);
// The most recent signal always needs special handling to find the frame
// pointer, but a nested signal does not. If pre_signal_frame_pointer is
// earlier in the stack than the old_frame_pointer, then use it. If it is
// later, then we have already unwound through it and it needs no special
// handling.
if (pre_signal_frame_pointer >= old_frame_pointer) {
new_frame_pointer = pre_signal_frame_pointer;
// The frame pointer should be 8-byte aligned.
if ((reinterpret_cast<uintptr_t>(new_frame_pointer) & 7) != 0)
return nullptr;
// Check that alleged frame pointer is actually readable. This is to
// prevent "double fault" in case we hit the first fault due to e.g.
// stack corruption.
if (!absl::debugging_internal::AddressIsReadable(
return nullptr;
// Only check the size if both frames are in the same stack.
if (InsideSignalStack(new_frame_pointer, stack_info) ==
InsideSignalStack(old_frame_pointer, stack_info)) {
// Check frame size. In strict mode, we assume frames to be under
// 100,000 bytes. In non-strict mode, we relax the limit to 1MB.
const size_t max_size = STRICT_UNWINDING ? 100000 : 1000000;
const size_t frame_size =
ComputeStackFrameSize(old_frame_pointer, new_frame_pointer);
if (frame_size == kUnknownFrameSize)
return nullptr;
// A very large frame may mean corrupt memory or an erroneous frame
// pointer. But also maybe just a plain-old large frame. Assume that if the
// frame is within a known stack, then it is valid.
if (frame_size > max_size) {
size_t stack_low = stack_info->stack_low;
size_t stack_high = stack_info->stack_high;
if (InsideSignalStack(new_frame_pointer, stack_info)) {
stack_low = stack_info->sig_stack_low;
stack_high = stack_info->sig_stack_high;
if (stack_high < kUnknownStackEnd &&
static_cast<size_t>(getpagesize()) < stack_low) {
const uintptr_t new_fp_u =
// Stack bounds are known.
if (!(stack_low < new_fp_u && new_fp_u <= stack_high)) {
// new_frame_pointer is not within a known stack.
return nullptr;
} else {
// Stack bounds are unknown, prefer truncated stack to possible crash.
return nullptr;
return new_frame_pointer;
template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
// We count on the bottom frame being this one. See the comment
// at prev_return_address
ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack.
ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack.
static int UnwindImpl(void** result, int* sizes, int max_depth, int skip_count,
const void *ucp, int *min_dropped_frames) {
#ifdef __GNUC__
void **frame_pointer = reinterpret_cast<void**>(__builtin_frame_address(0));
# error reading stack point not yet supported on this platform.
skip_count++; // Skip the frame for this function.
int n = 0;
// Assume that the first page is not stack.
StackInfo stack_info;
stack_info.stack_low = static_cast<uintptr_t>(getpagesize());
stack_info.stack_high = kUnknownStackEnd;
stack_info.sig_stack_low = stack_info.stack_low;
stack_info.sig_stack_high = kUnknownStackEnd;
// The frame pointer points to low address of a frame. The first 64-bit
// word of a frame points to the next frame up the call chain, which normally
// is just after the high address of the current frame. The second word of
// a frame contains return address of to the caller. To find a pc value
// associated with the current frame, we need to go down a level in the call
// chain. So we remember return the address of the last frame seen. This
// does not work for the first stack frame, which belongs to UnwindImp() but
// we skip the frame for UnwindImp() anyway.
void* prev_return_address = nullptr;
// The nth frame size is the difference between the nth frame pointer and the
// the frame pointer below it in the call chain. There is no frame below the
// leaf frame, but this function is the leaf anyway, and we skip it.
void** prev_frame_pointer = nullptr;
while (frame_pointer && n < max_depth) {
if (skip_count > 0) {
} else {
result[n] = prev_return_address;
sizes[n] = static_cast<int>(
ComputeStackFrameSize(prev_frame_pointer, frame_pointer));
prev_return_address = frame_pointer[1];
prev_frame_pointer = frame_pointer;
// The absl::GetStackFrames routine is called when we are in some
// informational context (the failure signal handler for example).
// Use the non-strict unwinding rules to produce a stack trace
// that is as complete as possible (even if it contains a few bogus
// entries in some rare cases).
frame_pointer = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(
frame_pointer, ucp, &stack_info);
if (min_dropped_frames != nullptr) {
// Implementation detail: we clamp the max of frames we are willing to
// count, so as not to spend too much time in the loop below.
const int kMaxUnwind = 200;
int num_dropped_frames = 0;
for (int j = 0; frame_pointer != nullptr && j < kMaxUnwind; j++) {
if (skip_count > 0) {
} else {
frame_pointer = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(
frame_pointer, ucp, &stack_info);
*min_dropped_frames = num_dropped_frames;
return n;
namespace absl {
namespace debugging_internal {
bool StackTraceWorksForTest() {
return true;
} // namespace debugging_internal
} // namespace absl