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Fix issues with .NET using signals as runtime instruments #301

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Merged
borrrden merged 2 commits into from
Jun 2, 2026
Merged

Fix issues with .NET using signals as runtime instruments #301

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5e02dda
Fix issues with .NET using signals as runtime instruments
borrrden Jun 2, 2026
50bde7a
Find libbacktrace when running either GCC or clang
borrrden Jun 2, 2026
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53 changes: 29 additions & 24 deletions Fleece/Support/Backtrace+signals-posix.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -62,9 +62,10 @@ namespace fleece {

for ( const int signal : signals) {
struct sigaction action{};
action.sa_flags = SA_SIGINFO | SA_ONSTACK | SA_NODEFER | SA_RESETHAND;
// NOTE: No SA_RESETHAND since on managed platforms signals are recoverable and
// we want our handler to keep working in the event that they are not
action.sa_flags = SA_SIGINFO | SA_ONSTACK;
sigfillset(&action.sa_mask);
sigdelset(&action.sa_mask, signal);
#if defined(__clang__)
# pragma clang diagnostic push
# pragma clang diagnostic ignored "-Wdisabled-macro-expansion"
Expand All @@ -91,11 +92,11 @@ namespace fleece {
unique_ptr<byte[]> _stack_content;

#ifdef __APPLE__
static constexpr array<int, 11> signals = {
#else
static constexpr array<int, 10> signals = {
#else
static constexpr array<int, 9> signals = {
#endif
SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGQUIT, SIGSEGV, SIGSYS, SIGTRAP, SIGXCPU, SIGXFSZ,
SIGABRT, SIGBUS, SIGFPE, SIGILL, SIGQUIT, SIGSEGV, SIGSYS, SIGTRAP, SIGXFSZ,
#if defined(__APPLE__)
SIGEMT,
#endif
Expand All @@ -111,37 +112,41 @@ namespace fleece {
NOINLINE static void crash_handler_immediate(siginfo_t* info, void* context) {
void* buffer[50];
int n = Backtrace::raw_capture(buffer, 50, context);
const char* name = strsignal(info->si_signo);
write_to_and_stderr(sLogFD, "\n\n******************** Process Crash: ", 38);
if ( name ) {
write_to_and_stderr(sLogFD, name);
} else {
write_to_and_stderr(sLogFD, "Signal: ", 8);
write_long(info->si_signo, sLogFD);
}
write_to_and_stderr(sLogFD, "\n\n******************** Signal caught: ", 38);
write_long(info->si_signo, sLogFD);

write_to_and_stderr(sLogFD, " Timestamp: ", 12);
char timestamp[20];
snprintf(timestamp, 20, "%lld", static_cast<long long>(time(nullptr)));
write_long(time(nullptr), sLogFD);

write_to_and_stderr(sLogFD, " *******************\n", 21);
Backtrace::writeTo(buffer + 3, n - 3, sLogFD);
write_to_and_stderr(sLogFD, "\n******************** Now terminating ********************\n", 59);
if ( sLogFD != -1 ) {
fsync(sLogFD);
close(sLogFD);
}
}

[[noreturn]] static void sig_handler(int signo, siginfo_t* info, void* context) {
crash_handler_immediate(info, context);

auto default_action = BacktraceSignalHandlerPosix::defaultActionFor(signo);
sigaction(signo, &default_action, nullptr);
raise(signo);
static void chain_to_previous(int signo, siginfo_t* info, void* context) {
const auto& prev = defaultActionFor(signo);
if ((prev.sa_flags & SA_SIGINFO) && prev.sa_sigaction && prev.sa_sigaction != &sig_handler) {
// Original fault context: the runtime can recover (and modify *context,
// which our return then resumes into) or die inside this call.
prev.sa_sigaction(signo, info, context);
} else if (prev.sa_handler && prev.sa_handler != SIG_IGN
&& prev.sa_handler != SIG_DFL) {
// SIG_IGN and SIG_DFL are not actual functions, don't try to call them
prev.sa_handler(signo);
} else if (prev.sa_handler == SIG_DFL) {
sigaction(signo, &prev, nullptr); // restore default and let it act
raise(signo); // fatal default terminates here
}
//SIG_IGN means ignore, so do just that
}

_exit(128 + signo);
static void sig_handler(int signo, siginfo_t* info, void* context) {
crash_handler_immediate(info, context);
chain_to_previous(signo, info, context);
write_to_and_stderr(sLogFD,
"\n********** Signal handled; execution continuing **********\n", 60);
}
};

Expand Down
24 changes: 10 additions & 14 deletions cmake/platform_linux.cmake
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Original file line number Diff line number Diff line change
@@ -1,19 +1,16 @@
include("${CMAKE_CURRENT_LIST_DIR}/platform_base.cmake")
include(CheckCXXSourceCompiles)

# libbacktrace is bundled inside GCC's private library directory.
# Ask GCC where it keeps the library and header so that builds with
# other compilers (e.g. Clang) can find it.
find_program(_gcc NAMES gcc)
if(_gcc)
# Both GCC and Clang support -print-file-name to locate bundled libraries.
if(CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
execute_process(
COMMAND ${_gcc} -print-file-name=libbacktrace.a
OUTPUT_VARIABLE _gcc_bt_lib OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_QUIET)
if(_gcc_bt_lib AND NOT _gcc_bt_lib STREQUAL "libbacktrace.a")
get_filename_component(_gcc_lib_dir "${_gcc_bt_lib}" DIRECTORY)
find_path(BACKTRACE_INCLUDE_DIR backtrace.h HINTS "${_gcc_lib_dir}/include")
COMMAND ${CMAKE_CXX_COMPILER} -print-file-name=libbacktrace.a
OUTPUT_VARIABLE _bt_lib OUTPUT_STRIP_TRAILING_WHITESPACE ERROR_QUIET)
if(_bt_lib AND NOT _bt_lib STREQUAL "libbacktrace.a")
get_filename_component(_bt_lib_dir "${_bt_lib}" DIRECTORY)
find_path(BACKTRACE_INCLUDE_DIR backtrace.h HINTS "${_bt_lib_dir}/include")
if(BACKTRACE_INCLUDE_DIR)
set(BACKTRACE_LIBRARY "${_gcc_bt_lib}")
set(BACKTRACE_LIBRARY "${_bt_lib}")
set(CMAKE_REQUIRED_INCLUDES "${BACKTRACE_INCLUDE_DIR}")
set(CMAKE_REQUIRED_LIBRARIES "${BACKTRACE_LIBRARY}")
check_cxx_source_compiles("
Expand All @@ -26,11 +23,10 @@ if(_gcc)
unset(CMAKE_REQUIRED_INCLUDES)
unset(CMAKE_REQUIRED_LIBRARIES)
endif()
unset(_bt_lib_dir)
endif()
unset(_gcc_bt_lib)
unset(_gcc_lib_dir)
unset(_bt_lib)
endif()
unset(_gcc)

function(set_source_files)
set(oneValueArgs RESULT)
Expand Down
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