370 lines
14 KiB
C++
370 lines
14 KiB
C++
// Copyright 2017 The Abseil Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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//
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// Produce stack trace
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#ifndef ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
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#define ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
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#if defined(__linux__) && (defined(__i386__) || defined(__x86_64__))
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#include <ucontext.h> // for ucontext_t
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#endif
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#if !defined(_WIN32)
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#include <unistd.h>
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#endif
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#include <cassert>
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#include <cstdint>
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#include <limits>
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#include "absl/base/macros.h"
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#include "absl/base/port.h"
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#include "absl/debugging/internal/address_is_readable.h"
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#include "absl/debugging/internal/vdso_support.h" // a no-op on non-elf or non-glibc systems
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#include "absl/debugging/stacktrace.h"
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#include "absl/base/internal/raw_logging.h"
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using absl::debugging_internal::AddressIsReadable;
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#if defined(__linux__) && defined(__i386__)
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// Count "push %reg" instructions in VDSO __kernel_vsyscall(),
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// preceeding "syscall" or "sysenter".
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// If __kernel_vsyscall uses frame pointer, answer 0.
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//
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// kMaxBytes tells how many instruction bytes of __kernel_vsyscall
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// to analyze before giving up. Up to kMaxBytes+1 bytes of
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// instructions could be accessed.
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//
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// Here are known __kernel_vsyscall instruction sequences:
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//
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// SYSENTER (linux-2.6.26/arch/x86/vdso/vdso32/sysenter.S).
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// Used on Intel.
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// 0xffffe400 <__kernel_vsyscall+0>: push %ecx
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// 0xffffe401 <__kernel_vsyscall+1>: push %edx
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// 0xffffe402 <__kernel_vsyscall+2>: push %ebp
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// 0xffffe403 <__kernel_vsyscall+3>: mov %esp,%ebp
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// 0xffffe405 <__kernel_vsyscall+5>: sysenter
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//
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// SYSCALL (see linux-2.6.26/arch/x86/vdso/vdso32/syscall.S).
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// Used on AMD.
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// 0xffffe400 <__kernel_vsyscall+0>: push %ebp
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// 0xffffe401 <__kernel_vsyscall+1>: mov %ecx,%ebp
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// 0xffffe403 <__kernel_vsyscall+3>: syscall
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//
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// The sequence below isn't actually expected in Google fleet,
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// here only for completeness. Remove this comment from OSS release.
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// i386 (see linux-2.6.26/arch/x86/vdso/vdso32/int80.S)
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// 0xffffe400 <__kernel_vsyscall+0>: int $0x80
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// 0xffffe401 <__kernel_vsyscall+1>: ret
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//
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static const int kMaxBytes = 10;
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// We use assert()s instead of DCHECK()s -- this is too low level
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// for DCHECK().
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static int CountPushInstructions(const unsigned char *const addr) {
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int result = 0;
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for (int i = 0; i < kMaxBytes; ++i) {
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if (addr[i] == 0x89) {
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// "mov reg,reg"
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if (addr[i + 1] == 0xE5) {
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// Found "mov %esp,%ebp".
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return 0;
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}
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++i; // Skip register encoding byte.
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} else if (addr[i] == 0x0F &&
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(addr[i + 1] == 0x34 || addr[i + 1] == 0x05)) {
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// Found "sysenter" or "syscall".
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return result;
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} else if ((addr[i] & 0xF0) == 0x50) {
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// Found "push %reg".
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++result;
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} else if (addr[i] == 0xCD && addr[i + 1] == 0x80) {
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// Found "int $0x80"
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assert(result == 0);
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return 0;
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} else {
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// Unexpected instruction.
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assert(false && "unexpected instruction in __kernel_vsyscall");
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return 0;
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}
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}
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// Unexpected: didn't find SYSENTER or SYSCALL in
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// [__kernel_vsyscall, __kernel_vsyscall + kMaxBytes) interval.
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assert(false && "did not find SYSENTER or SYSCALL in __kernel_vsyscall");
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return 0;
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}
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#endif
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// Assume stack frames larger than 100,000 bytes are bogus.
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static const int kMaxFrameBytes = 100000;
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// Returns the stack frame pointer from signal context, 0 if unknown.
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// vuc is a ucontext_t *. We use void* to avoid the use
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// of ucontext_t on non-POSIX systems.
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static uintptr_t GetFP(const void *vuc) {
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#if !defined(__linux__)
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static_cast<void>(vuc); // Avoid an unused argument compiler warning.
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#else
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if (vuc != nullptr) {
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auto *uc = reinterpret_cast<const ucontext_t *>(vuc);
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#if defined(__i386__)
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const auto bp = uc->uc_mcontext.gregs[REG_EBP];
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const auto sp = uc->uc_mcontext.gregs[REG_ESP];
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#elif defined(__x86_64__)
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const auto bp = uc->uc_mcontext.gregs[REG_RBP];
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const auto sp = uc->uc_mcontext.gregs[REG_RSP];
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#else
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const uintptr_t bp = 0;
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const uintptr_t sp = 0;
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#endif
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// Sanity-check that the base pointer is valid. It's possible that some
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// code in the process is compiled with --copt=-fomit-frame-pointer or
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// --copt=-momit-leaf-frame-pointer.
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//
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// TODO(bcmills): -momit-leaf-frame-pointer is currently the default
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// behavior when building with clang. Talk to the C++ toolchain team about
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// fixing that.
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if (bp >= sp && bp - sp <= kMaxFrameBytes) return bp;
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// If bp isn't a plausible frame pointer, return the stack pointer instead.
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// If we're lucky, it points to the start of a stack frame; otherwise, we'll
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// get one frame of garbage in the stack trace and fail the sanity check on
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// the next iteration.
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return sp;
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}
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#endif
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return 0;
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}
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// Given a pointer to a stack frame, locate and return the calling
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// stackframe, or return null if no stackframe can be found. Perform sanity
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// checks (the strictness of which is controlled by the boolean parameter
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// "STRICT_UNWINDING") to reduce the chance that a bad pointer is returned.
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template <bool STRICT_UNWINDING, bool WITH_CONTEXT>
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ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack.
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ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack.
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static void **NextStackFrame(void **old_fp, const void *uc,
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size_t stack_low, size_t stack_high) {
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void **new_fp = (void **)*old_fp;
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#if defined(__linux__) && defined(__i386__)
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if (WITH_CONTEXT && uc != nullptr) {
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// How many "push %reg" instructions are there at __kernel_vsyscall?
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// This is constant for a given kernel and processor, so compute
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// it only once.
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static int num_push_instructions = -1; // Sentinel: not computed yet.
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// Initialize with sentinel value: __kernel_rt_sigreturn can not possibly
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// be there.
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static const unsigned char *kernel_rt_sigreturn_address = nullptr;
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static const unsigned char *kernel_vsyscall_address = nullptr;
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if (num_push_instructions == -1) {
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#ifdef ABSL_HAVE_VDSO_SUPPORT
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absl::debugging_internal::VDSOSupport vdso;
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if (vdso.IsPresent()) {
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absl::debugging_internal::VDSOSupport::SymbolInfo
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rt_sigreturn_symbol_info;
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absl::debugging_internal::VDSOSupport::SymbolInfo vsyscall_symbol_info;
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if (!vdso.LookupSymbol("__kernel_rt_sigreturn", "LINUX_2.5", STT_FUNC,
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&rt_sigreturn_symbol_info) ||
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!vdso.LookupSymbol("__kernel_vsyscall", "LINUX_2.5", STT_FUNC,
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&vsyscall_symbol_info) ||
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rt_sigreturn_symbol_info.address == nullptr ||
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vsyscall_symbol_info.address == nullptr) {
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// Unexpected: 32-bit VDSO is present, yet one of the expected
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// symbols is missing or null.
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assert(false && "VDSO is present, but doesn't have expected symbols");
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num_push_instructions = 0;
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} else {
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kernel_rt_sigreturn_address =
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reinterpret_cast<const unsigned char *>(
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rt_sigreturn_symbol_info.address);
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kernel_vsyscall_address =
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reinterpret_cast<const unsigned char *>(
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vsyscall_symbol_info.address);
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num_push_instructions =
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CountPushInstructions(kernel_vsyscall_address);
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}
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} else {
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num_push_instructions = 0;
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}
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#else // ABSL_HAVE_VDSO_SUPPORT
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num_push_instructions = 0;
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#endif // ABSL_HAVE_VDSO_SUPPORT
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}
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if (num_push_instructions != 0 && kernel_rt_sigreturn_address != nullptr &&
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old_fp[1] == kernel_rt_sigreturn_address) {
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const ucontext_t *ucv = static_cast<const ucontext_t *>(uc);
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// This kernel does not use frame pointer in its VDSO code,
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// and so %ebp is not suitable for unwinding.
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void **const reg_ebp =
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reinterpret_cast<void **>(ucv->uc_mcontext.gregs[REG_EBP]);
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const unsigned char *const reg_eip =
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reinterpret_cast<unsigned char *>(ucv->uc_mcontext.gregs[REG_EIP]);
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if (new_fp == reg_ebp && kernel_vsyscall_address <= reg_eip &&
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reg_eip - kernel_vsyscall_address < kMaxBytes) {
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// We "stepped up" to __kernel_vsyscall, but %ebp is not usable.
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// Restore from 'ucv' instead.
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void **const reg_esp =
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reinterpret_cast<void **>(ucv->uc_mcontext.gregs[REG_ESP]);
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// Check that alleged %esp is not null and is reasonably aligned.
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if (reg_esp &&
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((uintptr_t)reg_esp & (sizeof(reg_esp) - 1)) == 0) {
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// Check that alleged %esp is actually readable. This is to prevent
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// "double fault" in case we hit the first fault due to e.g. stack
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// corruption.
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void *const reg_esp2 = reg_esp[num_push_instructions - 1];
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if (AddressIsReadable(reg_esp2)) {
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// Alleged %esp is readable, use it for further unwinding.
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new_fp = reinterpret_cast<void **>(reg_esp2);
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}
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}
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}
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}
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}
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#endif
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const uintptr_t old_fp_u = reinterpret_cast<uintptr_t>(old_fp);
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const uintptr_t new_fp_u = reinterpret_cast<uintptr_t>(new_fp);
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// Check that the transition from frame pointer old_fp to frame
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// pointer new_fp isn't clearly bogus. Skip the checks if new_fp
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// matches the signal context, so that we don't skip out early when
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// using an alternate signal stack.
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//
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// TODO(bcmills): The GetFP call should be completely unnecessary when
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// ENABLE_COMBINED_UNWINDER is set (because we should be back in the thread's
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// stack by this point), but it is empirically still needed (e.g. when the
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// stack includes a call to abort). unw_get_reg returns UNW_EBADREG for some
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// frames. Figure out why GetValidFrameAddr and/or libunwind isn't doing what
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// it's supposed to.
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if (STRICT_UNWINDING &&
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(!WITH_CONTEXT || uc == nullptr || new_fp_u != GetFP(uc))) {
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// With the stack growing downwards, older stack frame must be
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// at a greater address that the current one.
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if (new_fp_u <= old_fp_u) return nullptr;
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if (new_fp_u - old_fp_u > kMaxFrameBytes) return nullptr;
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if (stack_low < old_fp_u && old_fp_u <= stack_high) {
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// Old BP was in the expected stack region...
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if (!(stack_low < new_fp_u && new_fp_u <= stack_high)) {
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// ... but new BP is outside of expected stack region.
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// It is most likely bogus.
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return nullptr;
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}
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} else {
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// We may be here if we are executing in a co-routine with a
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// separate stack. We can't do safety checks in this case.
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}
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} else {
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if (new_fp == nullptr) return nullptr; // skip AddressIsReadable() below
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// In the non-strict mode, allow discontiguous stack frames.
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// (alternate-signal-stacks for example).
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if (new_fp == old_fp) return nullptr;
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}
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if (new_fp_u & (sizeof(void *) - 1)) return nullptr;
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#ifdef __i386__
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// On 32-bit machines, the stack pointer can be very close to
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// 0xffffffff, so we explicitly check for a pointer into the
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// last two pages in the address space
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if (new_fp_u >= 0xffffe000) return nullptr;
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#endif
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#if !defined(_WIN32)
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if (!STRICT_UNWINDING) {
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// Lax sanity checks cause a crash in 32-bit tcmalloc/crash_reason_test
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// on AMD-based machines with VDSO-enabled kernels.
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// Make an extra sanity check to insure new_fp is readable.
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// Note: NextStackFrame<false>() is only called while the program
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// is already on its last leg, so it's ok to be slow here.
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if (!AddressIsReadable(new_fp)) {
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return nullptr;
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}
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}
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#endif
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return new_fp;
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}
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template <bool IS_STACK_FRAMES, bool IS_WITH_CONTEXT>
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ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS // May read random elements from stack.
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ABSL_ATTRIBUTE_NO_SANITIZE_MEMORY // May read random elements from stack.
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ABSL_ATTRIBUTE_NOINLINE
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static int UnwindImpl(void **result, int *sizes, int max_depth, int skip_count,
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const void *ucp, int *min_dropped_frames) {
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int n = 0;
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void **fp = reinterpret_cast<void **>(__builtin_frame_address(0));
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size_t stack_low = getpagesize(); // Assume that the first page is not stack.
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size_t stack_high = std::numeric_limits<size_t>::max() - sizeof(void *);
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while (fp && n < max_depth) {
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if (*(fp + 1) == reinterpret_cast<void *>(0)) {
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// In 64-bit code, we often see a frame that
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// points to itself and has a return address of 0.
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break;
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}
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void **next_fp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(
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fp, ucp, stack_low, stack_high);
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if (skip_count > 0) {
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skip_count--;
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} else {
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result[n] = *(fp + 1);
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if (IS_STACK_FRAMES) {
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if (next_fp > fp) {
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sizes[n] = (uintptr_t)next_fp - (uintptr_t)fp;
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} else {
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// A frame-size of 0 is used to indicate unknown frame size.
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sizes[n] = 0;
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}
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}
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n++;
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}
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fp = next_fp;
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}
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if (min_dropped_frames != nullptr) {
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// Implementation detail: we clamp the max of frames we are willing to
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// count, so as not to spend too much time in the loop below.
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const int kMaxUnwind = 1000;
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int num_dropped_frames = 0;
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for (int j = 0; fp != nullptr && j < kMaxUnwind; j++) {
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if (skip_count > 0) {
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skip_count--;
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} else {
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num_dropped_frames++;
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}
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fp = NextStackFrame<!IS_STACK_FRAMES, IS_WITH_CONTEXT>(fp, ucp, stack_low,
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stack_high);
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}
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*min_dropped_frames = num_dropped_frames;
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}
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return n;
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}
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namespace absl {
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ABSL_NAMESPACE_BEGIN
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namespace debugging_internal {
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bool StackTraceWorksForTest() {
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return true;
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}
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} // namespace debugging_internal
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ABSL_NAMESPACE_END
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} // namespace absl
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#endif // ABSL_DEBUGGING_INTERNAL_STACKTRACE_X86_INL_INC_
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