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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/390223051): Remove C-library calls to fix the errors.
#pragma allow_unsafe_libc_calls
#endif
#include "base/debug/stack_trace.h"
#include <errno.h>
#include <fcntl.h>
#include <signal.h>
#include <stddef.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <unistd.h>
#include <algorithm>
#include <array>
#include <map>
#include <memory>
#include <ostream>
#include <string>
#include <tuple>
#include <vector>
#include "base/containers/heap_array.h"
#include "base/containers/span.h"
#include "base/containers/span_writer.h"
#include "base/memory/raw_ptr.h"
#include "base/strings/cstring_view.h"
#include "build/build_config.h"
// Controls whether `dladdr(...)` is used to print the callstack. This is
// only used on iOS Official build where `backtrace_symbols(...)` prints
// misleading symbols (as the binary is stripped).
#if BUILDFLAG(IS_IOS) && defined(OFFICIAL_BUILD)
#define HAVE_DLADDR
#include <dlfcn.h>
#endif
// Surprisingly, uClibc defines __GLIBC__ in some build configs, but
// execinfo.h and backtrace(3) are really only present in glibc and in macOS
// libc.
#if BUILDFLAG(IS_APPLE) || \
(defined(__GLIBC__) && !defined(__UCLIBC__) && !defined(__AIX))
#define HAVE_BACKTRACE
#include <execinfo.h>
#endif
// Controls whether to include code to demangle C++ symbols.
#if !defined(USE_SYMBOLIZE) && defined(HAVE_BACKTRACE) && !defined(HAVE_DLADDR)
#define DEMANGLE_SYMBOLS
#endif
#if defined(DEMANGLE_SYMBOLS)
#include <cxxabi.h>
#endif
#if BUILDFLAG(IS_APPLE)
#include <AvailabilityMacros.h>
#endif
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
#include <sys/prctl.h>
#include "base/debug/proc_maps_linux.h"
#endif
#include "base/cfi_buildflags.h"
#include "base/debug/debugger.h"
#include "base/debug/debugging_buildflags.h"
#include "base/debug/stack_trace.h"
#include "base/files/scoped_file.h"
#include "base/logging.h"
#include "base/memory/free_deleter.h"
#include "base/memory/singleton.h"
#include "base/numerics/safe_conversions.h"
#include "base/posix/eintr_wrapper.h"
#include "base/strings/string_number_conversions.h"
#include "base/strings/string_util.h"
#include "build/build_config.h"
#if defined(USE_SYMBOLIZE)
#include "base/third_party/symbolize/symbolize.h" // nogncheck
#if BUILDFLAG(ENABLE_STACK_TRACE_LINE_NUMBERS)
#include "base/debug/dwarf_line_no.h" // nogncheck
#endif
#endif
namespace base::debug {
namespace {
volatile sig_atomic_t in_signal_handler = 0;
bool (*try_handle_signal)(int, siginfo_t*, void*) = nullptr;
#if defined(DEMANGLE_SYMBOLS)
// The prefix used for mangled symbols, per the Itanium C++ ABI:
// http://www.codesourcery.com/cxx-abi/abi.html#mangling
const char kMangledSymbolPrefix[] = "_Z";
// Characters that can be used for symbols, generated by Ruby:
// (('a'..'z').to_a+('A'..'Z').to_a+('0'..'9').to_a + ['_']).join
const char kSymbolCharacters[] =
"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789_";
// Demangles C++ symbols in the given text. Example:
//
// "out/Debug/base_unittests(_ZN10StackTraceC1Ev+0x20) [0x817778c]"
// =>
// "out/Debug/base_unittests(StackTrace::StackTrace()+0x20) [0x817778c]"
void DemangleSymbols(std::string* text) {
// Note: code in this function is NOT async-signal safe (std::string uses
// malloc internally).
std::string::size_type search_from = 0;
while (search_from < text->size()) {
// Look for the start of a mangled symbol, from search_from.
std::string::size_type mangled_start =
text->find(kMangledSymbolPrefix, search_from);
if (mangled_start == std::string::npos) {
break; // Mangled symbol not found.
}
// Look for the end of the mangled symbol.
std::string::size_type mangled_end =
text->find_first_not_of(kSymbolCharacters, mangled_start);
if (mangled_end == std::string::npos) {
mangled_end = text->size();
}
std::string mangled_symbol =
text->substr(mangled_start, mangled_end - mangled_start);
// Try to demangle the mangled symbol candidate.
int status = 0;
std::unique_ptr<char, base::FreeDeleter> demangled_symbol(
abi::__cxa_demangle(mangled_symbol.c_str(), nullptr, 0, &status));
if (status == 0) { // Demangling is successful.
// Remove the mangled symbol.
text->erase(mangled_start, mangled_end - mangled_start);
// Insert the demangled symbol.
text->insert(mangled_start, demangled_symbol.get());
// Next time, we'll start right after the demangled symbol we inserted.
search_from = mangled_start + strlen(demangled_symbol.get());
} else {
// Failed to demangle. Retry after the "_Z" we just found.
search_from = mangled_start + 2;
}
}
}
#endif // defined(DEMANGLE_SYMBOLS)
class BacktraceOutputHandler {
public:
virtual void HandleOutput(const char* output) = 0;
protected:
virtual ~BacktraceOutputHandler() = default;
};
#if defined(HAVE_BACKTRACE)
void OutputPointer(const void* pointer, BacktraceOutputHandler* handler) {
// This should be more than enough to store a 64-bit number in hex:
// 16 hex digits + 1 for null-terminator.
char buf[17] = {'\0'};
handler->HandleOutput("0x");
internal::itoa_r(reinterpret_cast<intptr_t>(pointer), 16, 12, buf);
handler->HandleOutput(buf);
}
#if defined(HAVE_DLADDR) || defined(USE_SYMBOLIZE)
void OutputValue(size_t value, BacktraceOutputHandler* handler) {
// Max unsigned 64-bit number in decimal has 20 digits (18446744073709551615).
// Hence, 30 digits should be more than enough to represent it in decimal
// (including the null-terminator).
char buf[30] = {'\0'};
internal::itoa_r(static_cast<intptr_t>(value), 10, 1, buf);
handler->HandleOutput(buf);
}
#endif // defined(HAVE_DLADDR) || defined(USE_SYMBOLIZE)
#if defined(USE_SYMBOLIZE)
void OutputFrameId(size_t frame_id, BacktraceOutputHandler* handler) {
handler->HandleOutput("#");
OutputValue(frame_id, handler);
}
#endif // defined(USE_SYMBOLIZE)
void ProcessBacktrace(span<const void* const> traces,
cstring_view prefix_string,
BacktraceOutputHandler* handler) {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
// Don't exceed kMaxTraces or GetDwarfCompileUnitOffsets can go OOB.
traces = traces.first(std::min(traces.size(), StackTrace::kMaxTraces));
#if defined(USE_SYMBOLIZE)
#if BUILDFLAG(ENABLE_STACK_TRACE_LINE_NUMBERS)
std::array<uint64_t, StackTrace::kMaxTraces> cu_offsets = {};
GetDwarfCompileUnitOffsets(traces.data(), cu_offsets.data(), traces.size());
#endif
for (size_t i = 0; i < traces.size(); ++i) {
if (!prefix_string.empty()) {
handler->HandleOutput(prefix_string.c_str());
}
OutputFrameId(i, handler);
handler->HandleOutput(" ");
OutputPointer(traces[i], handler);
handler->HandleOutput(" ");
std::array<char, 1024> buf = {};
// Subtract by one as return address of function may be in the next function
// when a function is annotated as noreturn.
//
// SAFETY: The pointer here is not dereferenced, it is a program counter and
// it is used to look up an object file/function. It is treated as a
// `uintptr_t` inside Symbolize().
const void* address =
UNSAFE_BUFFERS(static_cast<const char*>(traces[i]) - 1);
if (google::Symbolize(const_cast<void*>(address), buf.data(), buf.size())) {
handler->HandleOutput(buf.data());
#if BUILDFLAG(ENABLE_STACK_TRACE_LINE_NUMBERS)
// Only output the source line number if the offset was found. Otherwise,
// it takes far too long in debug mode when there are lots of symbols.
if (GetDwarfSourceLineNumber(address, cu_offsets[i], buf.data(),
buf.size())) {
handler->HandleOutput(" [");
handler->HandleOutput(buf.data());
handler->HandleOutput("]");
}
#endif
} else {
handler->HandleOutput("<unknown>");
}
handler->HandleOutput("\n");
}
#else
bool printed = false;
// Below part is async-signal unsafe (uses malloc), so execute it only
// when we are not executing the signal handler.
if (in_signal_handler == 0 &&
IsValueInRangeForNumericType<int>(traces.size())) {
#if defined(HAVE_DLADDR)
Dl_info dl_info;
for (size_t i = 0; i < traces.size(); ++i) {
if (!prefix_string.empty()) {
handler->HandleOutput(prefix_string.c_str());
}
OutputValue(i, handler);
handler->HandleOutput(" ");
const bool dl_info_found = dladdr(traces[i], &dl_info) != 0;
if (dl_info_found) {
// SAFETY: dl_info::dli_fname is a NUL-terminated cstring.
auto dli_fname = UNSAFE_BUFFERS(base::cstring_view(dl_info.dli_fname));
if (size_t last_sep = dli_fname.rfind('/');
last_sep != base::cstring_view::npos) {
dli_fname.remove_prefix(last_sep + 1u);
}
handler->HandleOutput(dli_fname.c_str());
} else {
handler->HandleOutput("???");
}
handler->HandleOutput(" ");
OutputPointer(traces[i], handler);
handler->HandleOutput("\n");
}
printed = true;
#else // defined(HAVE_DLADDR)
auto trace_symbols =
// SAFETY: backtrace_symbols returns an allocated array of the same size
// as the input array, which is traces.size().
UNSAFE_BUFFERS(base::HeapArray<char*, FreeDeleter>::FromOwningPointer(
backtrace_symbols(const_cast<void* const*>(traces.data()),
static_cast<int>(traces.size())),
traces.size()));
if (!trace_symbols.empty()) {
for (char* s : trace_symbols) {
auto trace_symbol = std::string(s);
DemangleSymbols(&trace_symbol);
if (!prefix_string.empty()) {
handler->HandleOutput(prefix_string.c_str());
}
handler->HandleOutput(trace_symbol.c_str());
handler->HandleOutput("\n");
}
printed = true;
}
#endif // defined(HAVE_DLADDR)
}
if (!printed) {
for (const void* const trace : traces) {
handler->HandleOutput(" [");
OutputPointer(trace, handler);
handler->HandleOutput("]\n");
}
}
#endif // defined(USE_SYMBOLIZE)
}
#endif // defined(HAVE_BACKTRACE)
void PrintToStderr(const char* output) {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
std::ignore = HANDLE_EINTR(write(STDERR_FILENO, output, strlen(output)));
}
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_CHROMEOS)
void AlarmSignalHandler(int signal, siginfo_t* info, void* void_context) {
// We have seen rare cases on AMD linux where the default signal handler
// either does not run or a thread (Probably an AMD driver thread) prevents
// the termination of the gpu process. We catch this case when the alarm fires
// and then call exit_group() to kill all threads of the process. This has
// resolved the zombie gpu process issues we have seen on our context lost
// test.
// Note that many different calls were tried to kill the process when it is in
// this state. Only 'exit_group' was found to cause termination and it is
// speculated that only this works because only this exit kills all threads in
// the process (not simply the current thread).
// See: http://crbug.com/1396451.
PrintToStderr(
"Warning: Default signal handler failed to terminate process.\n");
PrintToStderr("Calling exit_group() directly to prevent timeout.\n");
// See: https://man7.org/linux/man-pages/man2/exit_group.2.html
syscall(SYS_exit_group, EXIT_FAILURE);
}
#endif // BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) ||
// BUILDFLAG(IS_CHROMEOS)
void StackDumpSignalHandler(int signal, siginfo_t* info, void* void_context) {
// NOTE: This code MUST be async-signal safe.
// NO malloc or stdio is allowed here.
// Give a registered callback a chance to recover from this signal
//
// V8 uses guard regions to guarantee memory safety in WebAssembly. This means
// some signals might be expected if they originate from Wasm code while
// accessing the guard region. We give V8 the chance to handle and recover
// from these signals first.
if (try_handle_signal != nullptr &&
try_handle_signal(signal, info, void_context)) {
// The first chance handler took care of this. The SA_RESETHAND flag
// replaced this signal handler upon entry, but we want to stay
// installed. Thus, we reinstall ourselves before returning.
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_flags = static_cast<int>(SA_RESETHAND | SA_SIGINFO);
action.sa_sigaction = &StackDumpSignalHandler;
sigemptyset(&action.sa_mask);
sigaction(signal, &action, nullptr);
return;
}
// Do not take the "in signal handler" code path on Mac in a DCHECK-enabled
// build, as this prevents seeing a useful (symbolized) stack trace on a crash
// or DCHECK() failure. While it may not be fully safe to run the stack symbol
// printing code, in practice it's better to provide meaningful stack traces -
// and the risk is low given we're likely crashing already.
#if !BUILDFLAG(IS_APPLE) || !DCHECK_IS_ON()
// Record the fact that we are in the signal handler now, so that the rest
// of StackTrace can behave in an async-signal-safe manner.
in_signal_handler = 1;
#endif
if (BeingDebugged()) {
BreakDebugger();
}
PrintToStderr("Received signal ");
char buf[1024] = {0};
internal::itoa_r(signal, 10, 0, buf);
PrintToStderr(buf);
if (signal == SIGBUS) {
if (info->si_code == BUS_ADRALN) {
PrintToStderr(" BUS_ADRALN ");
} else if (info->si_code == BUS_ADRERR) {
PrintToStderr(" BUS_ADRERR ");
} else if (info->si_code == BUS_OBJERR) {
PrintToStderr(" BUS_OBJERR ");
} else {
PrintToStderr(" <unknown> ");
}
} else if (signal == SIGFPE) {
if (info->si_code == FPE_FLTDIV) {
PrintToStderr(" FPE_FLTDIV ");
} else if (info->si_code == FPE_FLTINV) {
PrintToStderr(" FPE_FLTINV ");
} else if (info->si_code == FPE_FLTOVF) {
PrintToStderr(" FPE_FLTOVF ");
} else if (info->si_code == FPE_FLTRES) {
PrintToStderr(" FPE_FLTRES ");
} else if (info->si_code == FPE_FLTSUB) {
PrintToStderr(" FPE_FLTSUB ");
} else if (info->si_code == FPE_FLTUND) {
PrintToStderr(" FPE_FLTUND ");
} else if (info->si_code == FPE_INTDIV) {
PrintToStderr(" FPE_INTDIV ");
} else if (info->si_code == FPE_INTOVF) {
PrintToStderr(" FPE_INTOVF ");
} else {
PrintToStderr(" <unknown> ");
}
} else if (signal == SIGILL) {
if (info->si_code == ILL_BADSTK) {
PrintToStderr(" ILL_BADSTK ");
} else if (info->si_code == ILL_COPROC) {
PrintToStderr(" ILL_COPROC ");
} else if (info->si_code == ILL_ILLOPN) {
PrintToStderr(" ILL_ILLOPN ");
} else if (info->si_code == ILL_ILLADR) {
PrintToStderr(" ILL_ILLADR ");
} else if (info->si_code == ILL_ILLTRP) {
PrintToStderr(" ILL_ILLTRP ");
} else if (info->si_code == ILL_PRVOPC) {
PrintToStderr(" ILL_PRVOPC ");
} else if (info->si_code == ILL_PRVREG) {
PrintToStderr(" ILL_PRVREG ");
} else {
PrintToStderr(" <unknown> ");
}
} else if (signal == SIGSEGV) {
if (info->si_code == SEGV_MAPERR) {
PrintToStderr(" SEGV_MAPERR ");
} else if (info->si_code == SEGV_ACCERR) {
PrintToStderr(" SEGV_ACCERR ");
}
#if defined(ARCH_CPU_X86_64) && \
(BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_CHROMEOS))
else if (info->si_code == SI_KERNEL) {
PrintToStderr(" SI_KERNEL");
}
#endif
else {
PrintToStderr(" <unknown> ");
}
}
if (signal == SIGBUS || signal == SIGFPE || signal == SIGILL ||
signal == SIGSEGV) {
internal::itoa_r(reinterpret_cast<intptr_t>(info->si_addr), 16, 12, buf);
PrintToStderr(buf);
}
PrintToStderr("\n");
#if BUILDFLAG(CFI_ENFORCEMENT_TRAP)
if (signal == SIGILL && info->si_code == ILL_ILLOPN) {
PrintToStderr(
"CFI: Most likely a control flow integrity violation; for more "
"information see:\n");
PrintToStderr(
"https://www.chromium.org/developers/testing/control-flow-integrity\n");
}
#endif // BUILDFLAG(CFI_ENFORCEMENT_TRAP)
#if defined(ARCH_CPU_X86_64) && \
(BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_CHROMEOS))
if (signal == SIGSEGV && info->si_code == SI_KERNEL) {
PrintToStderr(
" Possibly a General Protection Fault, can be due to a non-canonical "
"address dereference. See \"Intel 64 and IA-32 Architectures Software "
"Developer’s Manual\", Volume 1, Section 3.3.7.1.\n");
}
#endif
debug::StackTrace().Print();
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
#if ARCH_CPU_X86_FAMILY
ucontext_t* context = reinterpret_cast<ucontext_t*>(void_context);
auto gregs = base::span(context->uc_mcontext.gregs);
struct Register {
const char* label;
greg_t value;
};
const auto registers = std::to_array<Register>({
#if ARCH_CPU_32_BITS
{" gs: ", gregs[REG_GS]}, {" fs: ", gregs[REG_FS]},
{" es: ", gregs[REG_ES]}, {" ds: ", gregs[REG_DS]},
{" edi: ", gregs[REG_EDI]}, {" esi: ", gregs[REG_ESI]},
{" ebp: ", gregs[REG_EBP]}, {" esp: ", gregs[REG_ESP]},
{" ebx: ", gregs[REG_EBX]}, {" edx: ", gregs[REG_EDX]},
{" ecx: ", gregs[REG_ECX]}, {" eax: ", gregs[REG_EAX]},
{" trp: ", gregs[REG_TRAPNO]}, {" err: ", gregs[REG_ERR]},
{" ip: ", gregs[REG_EIP]}, {" cs: ", gregs[REG_CS]},
{" efl: ", gregs[REG_EFL]}, {" usp: ", gregs[REG_UESP]},
{" ss: ", gregs[REG_SS]},
#elif ARCH_CPU_64_BITS
{" r8: ", gregs[REG_R8]}, {" r9: ", gregs[REG_R9]},
{" r10: ", gregs[REG_R10]}, {" r11: ", gregs[REG_R11]},
{" r12: ", gregs[REG_R12]}, {" r13: ", gregs[REG_R13]},
{" r14: ", gregs[REG_R14]}, {" r15: ", gregs[REG_R15]},
{" di: ", gregs[REG_RDI]}, {" si: ", gregs[REG_RSI]},
{" bp: ", gregs[REG_RBP]}, {" bx: ", gregs[REG_RBX]},
{" dx: ", gregs[REG_RDX]}, {" ax: ", gregs[REG_RAX]},
{" cx: ", gregs[REG_RCX]}, {" sp: ", gregs[REG_RSP]},
{" ip: ", gregs[REG_RIP]}, {" efl: ", gregs[REG_EFL]},
{" cgf: ", gregs[REG_CSGSFS]}, {" erf: ", gregs[REG_ERR]},
{" trp: ", gregs[REG_TRAPNO]}, {" msk: ", gregs[REG_OLDMASK]},
{" cr2: ", gregs[REG_CR2]},
#endif // ARCH_CPU_32_BITS
});
#if ARCH_CPU_32_BITS
const int kRegisterPadding = 8;
#elif ARCH_CPU_64_BITS
const int kRegisterPadding = 16;
#endif
for (size_t i = 0; i < std::size(registers); i++) {
PrintToStderr(registers[i].label);
internal::itoa_r(registers[i].value, 16, kRegisterPadding, buf);
PrintToStderr(buf);
if ((i + 1) % 4 == 0) {
PrintToStderr("\n");
}
}
PrintToStderr("\n");
#endif // ARCH_CPU_X86_FAMILY
#endif // BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
PrintToStderr("[end of stack trace]\n");
if (::signal(signal, SIG_DFL) == SIG_ERR) {
_exit(EXIT_FAILURE);
}
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) || BUILDFLAG(IS_CHROMEOS)
// Set an alarm to trigger in case the default handler does not terminate
// the process. See 'AlarmSignalHandler' for more details.
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_flags = static_cast<int>(SA_RESETHAND);
action.sa_sigaction = &AlarmSignalHandler;
sigemptyset(&action.sa_mask);
sigaction(SIGALRM, &action, nullptr);
// 'alarm' function is signal handler safe.
// https://man7.org/linux/man-pages/man7/signal-safety.7.html
// This delay is set to be long enough for the real signal handler to fire but
// shorter than chrome's process watchdog timer.
constexpr unsigned int kAlarmSignalDelaySeconds = 5;
alarm(kAlarmSignalDelaySeconds);
// The following is mostly from
// third_party/crashpad/crashpad/util/posix/signals.cc as re-raising signals
// is complicated.
// If we can raise a signal with siginfo on this platform, do so. This ensures
// that we preserve the siginfo information for asynchronous signals (i.e.
// signals that do not re-raise autonomously), such as signals delivered via
// kill() and asynchronous hardware faults such as SEGV_MTEAERR, which would
// otherwise be lost when re-raising the signal via raise().
long retval = syscall(SYS_rt_tgsigqueueinfo, getpid(), syscall(SYS_gettid),
info->si_signo, info);
if (retval == 0) {
return;
}
// Kernels without commit 66dd34ad31e5 ("signal: allow to send any siginfo to
// itself"), which was first released in kernel version 3.9, did not permit a
// process to send arbitrary signals to itself, and will reject the
// rt_tgsigqueueinfo syscall with EPERM. If that happens, follow the non-Linux
// code path. Any other errno is unexpected and will cause us to exit.
if (errno != EPERM) {
_exit(EXIT_FAILURE);
}
#endif // BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_ANDROID) ||
// BUILDFLAG(IS_CHROMEOS)
// Explicitly re-raise the signal even if it might have re-raised itself on
// return. Because signal handlers normally execute with their signal blocked,
// this raise() cannot immediately deliver the signal. Delivery is deferred
// until the signal handler returns and the signal becomes unblocked. The
// re-raised signal will appear with the same context as where it was
// initially triggered.
if (raise(signal) != 0) {
_exit(EXIT_FAILURE);
}
}
class PrintBacktraceOutputHandler : public BacktraceOutputHandler {
public:
PrintBacktraceOutputHandler() = default;
PrintBacktraceOutputHandler(const PrintBacktraceOutputHandler&) = delete;
PrintBacktraceOutputHandler& operator=(const PrintBacktraceOutputHandler&) =
delete;
void HandleOutput(const char* output) override {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
PrintToStderr(output);
}
};
class StreamBacktraceOutputHandler : public BacktraceOutputHandler {
public:
explicit StreamBacktraceOutputHandler(std::ostream* os) : os_(os) {}
StreamBacktraceOutputHandler(const StreamBacktraceOutputHandler&) = delete;
StreamBacktraceOutputHandler& operator=(const StreamBacktraceOutputHandler&) =
delete;
void HandleOutput(const char* output) override { (*os_) << output; }
private:
raw_ptr<std::ostream> os_;
};
void WarmUpBacktrace() {
// Warm up stack trace infrastructure. It turns out that on the first
// call glibc initializes some internal data structures using pthread_once,
// and even backtrace() can call malloc(), leading to hangs.
//
// Example stack trace snippet (with tcmalloc):
//
// #8 0x0000000000a173b5 in tc_malloc
// at ./third_party/tcmalloc/chromium/src/debugallocation.cc:1161
// #9 0x00007ffff7de7900 in _dl_map_object_deps at dl-deps.c:517
// #10 0x00007ffff7ded8a9 in dl_open_worker at dl-open.c:262
// #11 0x00007ffff7de9176 in _dl_catch_error at dl-error.c:178
// #12 0x00007ffff7ded31a in _dl_open (file=0x7ffff625e298 "libgcc_s.so.1")
// at dl-open.c:639
// #13 0x00007ffff6215602 in do_dlopen at dl-libc.c:89
// #14 0x00007ffff7de9176 in _dl_catch_error at dl-error.c:178
// #15 0x00007ffff62156c4 in dlerror_run at dl-libc.c:48
// #16 __GI___libc_dlopen_mode at dl-libc.c:165
// #17 0x00007ffff61ef8f5 in init
// at ../sysdeps/x86_64/../ia64/backtrace.c:53
// #18 0x00007ffff6aad400 in pthread_once
// at ../nptl/sysdeps/unix/sysv/linux/x86_64/pthread_once.S:104
// #19 0x00007ffff61efa14 in __GI___backtrace
// at ../sysdeps/x86_64/../ia64/backtrace.c:104
// #20 0x0000000000752a54 in base::debug::StackTrace::StackTrace
// at base/debug/stack_trace_posix.cc:175
// #21 0x00000000007a4ae5 in
// base::(anonymous namespace)::StackDumpSignalHandler
// at base/process_util_posix.cc:172
// #22 <signal handler called>
StackTrace stack_trace;
}
#if defined(USE_SYMBOLIZE)
// class SandboxSymbolizeHelper.
//
// The purpose of this class is to prepare and install a "file open" callback
// needed by the stack trace symbolization code
// (base/third_party/symbolize/symbolize.h) so that it can function properly
// in a sandboxed process. The caveat is that this class must be instantiated
// before the sandboxing is enabled so that it can get the chance to open all
// the object files that are loaded in the virtual address space of the current
// process.
class SandboxSymbolizeHelper {
public:
// Returns the singleton instance.
static SandboxSymbolizeHelper* GetInstance() {
return Singleton<SandboxSymbolizeHelper,
LeakySingletonTraits<SandboxSymbolizeHelper>>::get();
}
SandboxSymbolizeHelper(const SandboxSymbolizeHelper&) = delete;
SandboxSymbolizeHelper& operator=(const SandboxSymbolizeHelper&) = delete;
private:
friend struct DefaultSingletonTraits<SandboxSymbolizeHelper>;
SandboxSymbolizeHelper() { Init(); }
~SandboxSymbolizeHelper() {
UnregisterCallback();
CloseObjectFiles();
}
// Returns a O_RDONLY file descriptor for |file_path| if it was opened
// successfully during the initialization. The file is repositioned at
// offset 0.
// IMPORTANT: This function must be async-signal-safe because it can be
// called from a signal handler (symbolizing stack frames for a crash).
int GetFileDescriptor(const char* file_path) {
int fd = -1;
#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
if (file_path) {
// The assumption here is that iterating over std::map<std::string,
// base::ScopedFD> does not allocate dynamic memory, hence it is
// async-signal-safe.
for (const auto& filepath_fd : modules_) {
if (strcmp(filepath_fd.first.c_str(), file_path) == 0) {
// POSIX.1-2004 requires an implementation to guarantee that dup()
// is async-signal-safe.
fd = HANDLE_EINTR(dup(filepath_fd.second.get()));
break;
}
}
// POSIX.1-2004 requires an implementation to guarantee that lseek()
// is async-signal-safe.
if (fd >= 0 && lseek(fd, 0, SEEK_SET) < 0) {
// Failed to seek.
fd = -1;
}
}
#endif // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
return fd;
}
// Searches for the object file (from /proc/self/maps) that contains
// the specified pc. If found, sets |start_address| to the start address
// of where this object file is mapped in memory, sets the module base
// address into |base_address|, copies the object file name into
// |out_file_name|, and attempts to open the object file. If the object
// file is opened successfully, returns the file descriptor. Otherwise,
// returns -1.
// IMPORTANT: This function must be async-signal-safe because it can be
// called from a signal handler (symbolizing stack frames for a crash).
static int OpenObjectFileContainingPc(uint64_t pc,
uint64_t& start_address,
uint64_t& base_address,
char* file_path_ptr,
size_t file_path_size) {
auto file_path =
// SAFETY: This function is given as a function pointer to
// google::InstallSymbolizeOpenObjectFileCallback. It provides
// `file_path_size` as the size of the string in `file_path_ptr`,
// including a NUL terminator. Via code inspection we can see that
// `file_path_ptr` can be null, in which case `file_path_size` is zero.
UNSAFE_BUFFERS(base::span(file_path_ptr, file_path_size));
// This method can only be called after the singleton is instantiated.
// This is ensured by the following facts:
// * This is the only static method in this class, it is private, and
// the class has no friends (except for the DefaultSingletonTraits).
// The compiler guarantees that it can only be called after the
// singleton is instantiated.
// * This method is used as a callback for the stack tracing code and
// the callback registration is done in the constructor, so logically
// it cannot be called before the singleton is created.
SandboxSymbolizeHelper* instance = GetInstance();
// Cannot use STL iterators here, since debug iterators use locks.
// NOLINTNEXTLINE(modernize-loop-convert)
for (size_t i = 0; i < instance->regions_.size(); ++i) {
const MappedMemoryRegion& region = instance->regions_[i];
// We overwrite the file_path with the if `pc` is within a
// MemoryMappedRegion.
if (region.start <= pc && pc < region.end) {
start_address = region.start;
base_address = region.base;
if (!file_path.empty()) {
strlcpy(file_path, region.path);
}
return instance->GetFileDescriptor(region.path.c_str());
}
}
return -1;
}
// This class is copied from
// third_party/crashpad/crashpad/util/linux/scoped_pr_set_dumpable.h.
// It aims at ensuring the process is dumpable before opening /proc/self/mem.
// If the process is already dumpable, this class doesn't do anything.
class ScopedPrSetDumpable {
public:
// Uses `PR_SET_DUMPABLE` to make the current process dumpable.
//
// Restores the dumpable flag to its original value on destruction. If the
// original value couldn't be determined, the destructor attempts to
// restore the flag to 0 (non-dumpable).
explicit ScopedPrSetDumpable() {
int result = prctl(PR_GET_DUMPABLE, 0, 0, 0, 0);
was_dumpable_ = result > 0;
if (!was_dumpable_) {
std::ignore = prctl(PR_SET_DUMPABLE, 1, 0, 0, 0);
}
}
ScopedPrSetDumpable(const ScopedPrSetDumpable&) = delete;
ScopedPrSetDumpable& operator=(const ScopedPrSetDumpable&) = delete;
~ScopedPrSetDumpable() {
if (!was_dumpable_) {
std::ignore = prctl(PR_SET_DUMPABLE, 0, 0, 0, 0);
}
}
private:
bool was_dumpable_;
};
// Set the base address for each memory region by reading ELF headers in
// process memory.
void SetBaseAddressesForMemoryRegions() {
base::ScopedFD mem_fd;
{
ScopedPrSetDumpable s;
mem_fd = base::ScopedFD(
HANDLE_EINTR(open("/proc/self/mem", O_RDONLY | O_CLOEXEC)));
if (!mem_fd.is_valid()) {
return;
}
}
auto safe_memcpy = [&mem_fd](void* dst, uintptr_t src, size_t size) {
return HANDLE_EINTR(pread(mem_fd.get(), dst, size,
static_cast<off_t>(src))) == ssize_t(size);
};
uintptr_t cur_base = 0;
for (auto& r : regions_) {
ElfW(Ehdr) ehdr;
static_assert(SELFMAG <= sizeof(ElfW(Ehdr)), "SELFMAG too large");
if ((r.permissions & MappedMemoryRegion::READ) &&
safe_memcpy(&ehdr, r.start, sizeof(ElfW(Ehdr))) &&
memcmp(ehdr.e_ident, ELFMAG, SELFMAG) == 0) {
switch (ehdr.e_type) {
case ET_EXEC:
cur_base = 0;
break;
case ET_DYN:
// Find the segment containing file offset 0. This will correspond
// to the ELF header that we just read. Normally this will have
// virtual address 0, but this is not guaranteed. We must subtract
// the virtual address from the address where the ELF header was
// mapped to get the base address.
//
// If we fail to find a segment for file offset 0, use the address
// of the ELF header as the base address.
cur_base = r.start;
for (unsigned i = 0; i != ehdr.e_phnum; ++i) {
ElfW(Phdr) phdr;
if (safe_memcpy(&phdr, r.start + ehdr.e_phoff + i * sizeof(phdr),
sizeof(phdr)) &&
phdr.p_type == PT_LOAD && phdr.p_offset == 0) {
cur_base = r.start - phdr.p_vaddr;
break;
}
}
break;
default:
// ET_REL or ET_CORE. These aren't directly executable, so they
// don't affect the base address.
break;
}
}
r.base = cur_base;
}
}
// Parses /proc/self/maps in order to compile a list of all object file names
// for the modules that are loaded in the current process.
// Returns true on success.
bool CacheMemoryRegions() {
// Reads /proc/self/maps.
std::string contents;
if (!ReadProcMaps(&contents)) {
LOG(ERROR) << "Failed to read /proc/self/maps";
return false;
}
// Parses /proc/self/maps.
if (!ParseProcMaps(contents, &regions_)) {
LOG(ERROR) << "Failed to parse the contents of /proc/self/maps";
return false;
}
SetBaseAddressesForMemoryRegions();
is_initialized_ = true;
return true;
}
// Opens all object files and caches their file descriptors.
void OpenSymbolFiles() {
// Pre-opening and caching the file descriptors of all loaded modules is
// not safe for production builds. Hence it is only done in non-official
// builds. For more details, take a look at: http://crbug.com/341966.
#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
// Open the object files for all read-only executable regions and cache
// their file descriptors.
std::vector<MappedMemoryRegion>::const_iterator it;
for (it = regions_.begin(); it != regions_.end(); ++it) {
const MappedMemoryRegion& region = *it;
// Only interesed in read-only executable regions.
if ((region.permissions & MappedMemoryRegion::READ) ==
MappedMemoryRegion::READ &&
(region.permissions & MappedMemoryRegion::WRITE) == 0 &&
(region.permissions & MappedMemoryRegion::EXECUTE) ==
MappedMemoryRegion::EXECUTE) {
if (region.path.empty()) {
// Skip regions with empty file names.
continue;
}
if (region.path[0] == '[') {
// Skip pseudo-paths, like [stack], [vdso], [heap], etc ...
continue;
}
if (base::EndsWith(region.path, " (deleted)",
base::CompareCase::SENSITIVE)) {
// Skip deleted files.
continue;
}
// Avoid duplicates.
if (modules_.find(region.path) == modules_.end()) {
int fd = open(region.path.c_str(), O_RDONLY | O_CLOEXEC);
if (fd >= 0) {
modules_.emplace(region.path, base::ScopedFD(fd));
} else {
PLOG(WARNING) << "Failed to open file: " << region.path;
}
}
}
}
#endif // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
}
// Initializes and installs the symbolization callback.
void Init() {
if (CacheMemoryRegions()) {
OpenSymbolFiles();
google::InstallSymbolizeOpenObjectFileCallback(
&OpenObjectFileContainingPc);
}
}
// Unregister symbolization callback.
void UnregisterCallback() {
if (is_initialized_) {
google::InstallSymbolizeOpenObjectFileCallback(nullptr);
is_initialized_ = false;
}
}
// Closes all file descriptors owned by this instance.
void CloseObjectFiles() {
#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
modules_.clear();
#endif // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
}
// Set to true upon successful initialization.
bool is_initialized_ = false;
#if !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
// Mapping from file name to file descriptor. Includes file descriptors
// for all successfully opened object files and the file descriptor for
// /proc/self/maps. This code is not safe for production builds.
std::map<std::string, base::ScopedFD> modules_;
#endif // !defined(OFFICIAL_BUILD) || !defined(NO_UNWIND_TABLES)
// Cache for the process memory regions. Produced by parsing the contents
// of /proc/self/maps cache.
std::vector<MappedMemoryRegion> regions_;
};
#endif // USE_SYMBOLIZE
} // namespace
bool EnableInProcessStackDumping() {
#if defined(USE_SYMBOLIZE)
SandboxSymbolizeHelper::GetInstance();
#endif // USE_SYMBOLIZE
// When running in an application, our code typically expects SIGPIPE
// to be ignored. Therefore, when testing that same code, it should run
// with SIGPIPE ignored as well.
struct sigaction sigpipe_action;
memset(&sigpipe_action, 0, sizeof(sigpipe_action));
sigpipe_action.sa_handler = SIG_IGN;
sigemptyset(&sigpipe_action.sa_mask);
bool success = (sigaction(SIGPIPE, &sigpipe_action, nullptr) == 0);
// Avoid hangs during backtrace initialization, see above.
WarmUpBacktrace();
struct sigaction action;
memset(&action, 0, sizeof(action));
action.sa_flags = static_cast<int>(SA_RESETHAND | SA_SIGINFO);
action.sa_sigaction = &StackDumpSignalHandler;
sigemptyset(&action.sa_mask);
success &= (sigaction(SIGILL, &action, nullptr) == 0);
success &= (sigaction(SIGABRT, &action, nullptr) == 0);
success &= (sigaction(SIGFPE, &action, nullptr) == 0);
success &= (sigaction(SIGBUS, &action, nullptr) == 0);
success &= (sigaction(SIGSEGV, &action, nullptr) == 0);
// On Linux, SIGSYS is reserved by the kernel for seccomp-bpf sandboxing.
#if !BUILDFLAG(IS_LINUX) && !BUILDFLAG(IS_CHROMEOS)
success &= (sigaction(SIGSYS, &action, nullptr) == 0);
#endif // !BUILDFLAG(IS_LINUX) && !BUILDFLAG(IS_CHROMEOS)
return success;
}
bool SetStackDumpFirstChanceCallback(bool (*handler)(int, siginfo_t*, void*)) {
DCHECK(try_handle_signal == nullptr || handler == nullptr);
try_handle_signal = handler;
#if defined(ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER) || \
defined(UNDEFINED_SANITIZER)
struct sigaction installed_handler;
CHECK_EQ(sigaction(SIGSEGV, NULL, &installed_handler), 0);
// If the installed handler does not point to StackDumpSignalHandler, then
// allow_user_segv_handler is 0.
if (installed_handler.sa_sigaction != StackDumpSignalHandler) {
LOG(WARNING)
<< "WARNING: sanitizers are preventing signal handler installation. "
<< "WebAssembly trap handlers are disabled.\n";
return false;
}
#endif
return true;
}
size_t CollectStackTrace(span<const void*> trace) {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
#if defined(NO_UNWIND_TABLES) && BUILDFLAG(CAN_UNWIND_WITH_FRAME_POINTERS)
// If we do not have unwind tables, then try tracing using frame pointers.
return base::debug::TraceStackFramePointers(trace, 0);
#elif defined(HAVE_BACKTRACE)
// Though the backtrace API man page does not list any possible negative
// return values, we take no chance.
return base::saturated_cast<size_t>(
backtrace(const_cast<void**>(trace.data()),
base::saturated_cast<int>(trace.size())));
#else
return 0;
#endif
}
// static
void StackTrace::PrintMessageWithPrefix(cstring_view prefix_string,
cstring_view message) {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
if (!prefix_string.empty()) {
PrintToStderr(prefix_string.c_str());
}
PrintToStderr(message.c_str());
}
void StackTrace::PrintWithPrefixImpl(cstring_view prefix_string) const {
// NOTE: This code MUST be async-signal safe (it's used by in-process
// stack dumping signal handler). NO malloc or stdio is allowed here.
#if defined(HAVE_BACKTRACE)
PrintBacktraceOutputHandler handler;
ProcessBacktrace(addresses(), prefix_string, &handler);
#endif
}
#if defined(HAVE_BACKTRACE)
void StackTrace::OutputToStreamWithPrefixImpl(
std::ostream* os,
cstring_view prefix_string) const {
StreamBacktraceOutputHandler handler(os);
ProcessBacktrace(addresses(), prefix_string, &handler);
}
#endif
namespace internal {
// NOTE: code from sandbox/linux/seccomp-bpf/demo.cc.
// Modified to use bounds-checked containers.
void itoa_r(intptr_t i, int base, size_t padding, base::span<char> buf) {
// Make sure we can write at least one NUL byte.
if (buf.empty()) {
return;
}
if (base < 2 || base > 16) {
buf[0u] = '\000';
return;
}
auto writer = base::SpanWriter(buf);
size_t start = 0u;
uintptr_t j = static_cast<uintptr_t>(i);
// Handle negative numbers (only for base 10).
if (i < 0 && base == 10) {
// This does "j = -i" while avoiding integer overflow.
j = static_cast<uintptr_t>(-(i + 1)) + 1;
// Make sure we can write the '-' character.
if (!writer.Write('-')) {
buf[0u] = '\000';
return;
}
start += 1u; // The number starts after the sign.
}
// Loop until we have converted the entire number. Output at least one
// character (i.e. '0').
constexpr std::string_view digits = "0123456789abcdef";
do {
// Output the next digit.
if (!writer.Write(digits[j % static_cast<uintptr_t>(base)])) {
buf[0] = '\000';
return;
}
j /= static_cast<uintptr_t>(base);
if (padding > 0) {
padding--;
}
} while (j > 0 || padding > 0);
// Terminate the output with a NUL character.
if (!writer.Write('\000')) {
buf[0] = '\000';
return;
}
// Conversion to ASCII actually resulted in the digits being in reverse order.
// We can't easily generate them in forward order, as we can't tell the number
// of characters needed until we are done converting. So, now, we reverse the
// string (except for the possible "-" sign and the NUL terminator).
std::ranges::reverse(buf.first(writer.num_written() - 1u).subspan(start));
}
} // namespace internal
} // namespace base::debug