#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_ #define ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_ // Generate stack tracer for aarch64 #if defined(__linux__) #include <sys/mman.h> #include <ucontext.h> #include <unistd.h> #endif #include <atomic> #include <cassert> #include <cstdint> #include <iostream> #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 uintptr_t kUnknownFrameSize = 0; #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; 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); #ifdef ABSL_HAVE_VDSO_SUPPORT absl::debug_internal::VDSOSupport vdso; if (vdso.IsPresent()) { absl::debug_internal::VDSOSupport::SymbolInfo symbol_info; if (!vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_2.6.39", STT_FUNC, &symbol_info) || 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 memoized.store(address, 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 inline uintptr_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 ? high_char_ptr - low_char_ptr : kUnknownFrameSize; } // 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. template<bool STRICT_UNWINDING, bool WITH_CONTEXT> static void **NextStackFrame(void **old_frame_pointer, const void *uc) { void **new_frame_pointer = reinterpret_cast<void**>(*old_frame_pointer); bool check_frame_size = true; #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]); // 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::debug_internal::AddressIsReadable( pre_signal_frame_pointer)) return nullptr; // Alleged frame pointer is readable, use it for further unwinding. new_frame_pointer = pre_signal_frame_pointer; // Skip frame size check if we return from a signal. We may be using a // an alternate stack for signals. check_frame_size = false; } } #endif // aarch64 ABI requires stack pointer to be 16-byte-aligned. if ((reinterpret_cast<uintptr_t>(new_frame_pointer) & 15) != 0) return nullptr; // 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. if (check_frame_size) { const uintptr_t max_size = STRICT_UNWINDING ? 100000 : 1000000; const uintptr_t frame_size = ComputeStackFrameSize(old_frame_pointer, new_frame_pointer); if (frame_size == kUnknownFrameSize || frame_size > max_size) return nullptr; } return new_frame_pointer; } template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT> 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)); #else # error reading stack point not yet supported on this platform. #endif skip_count++; // Skip the frame for this function. int n = 0; // 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 adress 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; while (frame_pointer && n < max_depth) { // 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). void **next_frame_pointer = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp); if (skip_count > 0) { skip_count--; } else { result[n] = prev_return_address; if (IS_STACK_FRAMES) { sizes[n] = ComputeStackFrameSize(frame_pointer, next_frame_pointer); } n++; } prev_return_address = frame_pointer[1]; frame_pointer = next_frame_pointer; } 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 j = 0; for (; frame_pointer != nullptr && j < kMaxUnwind; j++) { frame_pointer = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(frame_pointer, ucp); } *min_dropped_frames = j; } return n; } #endif // ABSL_DEBUGGING_INTERNAL_STACKTRACE_AARCH64_INL_H_