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// Copyright 2021 The Abseil Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_RISCV_INL_H_
#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_RISCV_INL_H_
// Generate stack trace for riscv
#include <sys/ucontext.h>
#include "absl/base/config.h"
#if defined(__linux__)
#include <sys/mman.h>
#include <ucontext.h>
#include <unistd.h>
#endif
#include <atomic>
#include <cassert>
#include <cstdint>
#include <iostream>
#include "absl/base/attributes.h"
#include "absl/debugging/internal/address_is_readable.h"
#include "absl/debugging/internal/vdso_support.h"
#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 = 0;
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);
#if ABSL_HAVE_VDSO_SUPPORT
absl::debugging_internal::VDSOSupport vdso;
if (vdso.IsPresent()) {
absl::debugging_internal::VDSOSupport::SymbolInfo symbol_info;
// Symbol versioning pulled from arch/riscv/kernel/vdso/vdso.lds at v5.10.
auto lookup = [&](int type) {
return vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_4.15", type,
&symbol_info);
};
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
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>
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) {
// .
// .
// .
// +-> +----------------+
// | | return address |
// | | previous fp |
// | | ... |
// | +----------------+ <-+
// | | return address | |
// +---|- previous fp | |
// | ... | |
// $fp ->|----------------+ |
// | return address | |
// | previous fp -|---+
// $sp ->| ... |
// +----------------+
void **new_frame_pointer = reinterpret_cast<void **>(old_frame_pointer[-2]);
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 is not suitable for unwinding, look at ucontext to
// discover frame pointer before signal.
//
// RISCV ELF psABI has the frame pointer at x8/fp/s0.
// -- RISCV psABI Table 18.2
void **const pre_signal_frame_pointer =
reinterpret_cast<void **>(ucv->uc_mcontext.__gregs[8]);
// Check the alleged frame pointer is actually readable. This is to
// prevent "double fault" in case we hit the first fault due to stack
// corruption.
if (!absl::debugging_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 an
// alterate stack for signals.
check_frame_size = false;
}
}
#endif
// The RISCV ELF psABI mandates that the stack pointer is always 16-byte
// aligned.
// FIXME(abdulras) this doesn't hold for ILP32E which only mandates a 4-byte
// alignment.
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>
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) {
#if defined(__GNUC__)
void **frame_pointer = reinterpret_cast<void **>(__builtin_frame_address(0));
#else
#error reading stack pointer not yet supported on this platform
#endif
skip_count++; // Skip the frame for this function.
int n = 0;
// The `frame_pointer` that is computed here points to the top of the frame.
// The two words preceding the address are the return address and the previous
// frame pointer. To find a PC value associated with the current frame, we
// need to go down a level in the call chain. So we remember the return
// 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 si 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;
}
namespace absl {
ABSL_NAMESPACE_BEGIN
namespace debugging_internal {
bool StackTraceWorksForTest() { return true; }
} // namespace debugging_internal
ABSL_NAMESPACE_END
} // namespace absl
#endif
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