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fix(crash): replace async-signal-unsafe TLS with pthread-specifics #8271

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fix(crash): replace async-signal-unsafe TLS with pthread-specifics #8271

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0ae2b28
fix(crash): replace async-signal-unsafe TLS with pre-allocated table
jpnurmi Jun 29, 2026
10ec32a
fix(crash): Consume signal ignore on any signal delivery
jpnurmi Jun 29, 2026
078c799
fix(crash): Use atomic stores for signal ignore ring buffer slots
jpnurmi Jun 29, 2026
ce4b25d
fix(crash): single atomic uint64 for signal ignore entries
jpnurmi Jun 29, 2026
ecebb23
fix(crash): Use 16-byte atomic struct for signal ignore entries
jpnurmi Jun 29, 2026
ed65745
fix(crash): Use pthread-specific ignored signals
jpnurmi Jul 8, 2026
62c4578
fix(crash): Publish ignore entry before activation
jpnurmi Jul 9, 2026
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84 changes: 70 additions & 14 deletions Sources/SentryCrash/Recording/Monitors/SentryCrashMonitor_Signal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -38,19 +38,36 @@
#if SENTRY_HAS_SIGNAL

# include <errno.h>
# include <pthread.h>
# include <signal.h>
# include <stdatomic.h>
# include <stdint.h>
# include <stdio.h>
# include <stdlib.h>
# include <string.h>

// ============================================================================
# pragma mark - Types -
// ============================================================================

# ifdef SENTRY_CRASH_MANAGED_RUNTIME
typedef struct SentryCrashIgnoreSignal {
_Atomic uintptr_t tid;
_Atomic int signum;
struct SentryCrashIgnoreSignal *next;
} SentryCrashIgnoreSignal;
# endif

// ============================================================================
# pragma mark - Globals -
// ============================================================================

static volatile bool g_isEnabled = false;
static bool g_isSigtermReportingEnabled = false;
# ifdef SENTRY_CRASH_MANAGED_RUNTIME
static _Thread_local int tl_ignoreSignum = 0;
static _Atomic(SentryCrashIgnoreSignal *) g_ignoreSignals = NULL;
static pthread_key_t g_ignoreSignalKey;
static pthread_once_t g_ignoreSignalKeyOnce = PTHREAD_ONCE_INIT;
# endif

static SentryCrash_MonitorContext g_monitorContext;
Expand Down Expand Up @@ -83,6 +100,22 @@ restorePreviousSignalHandler(int sigNum)
}
}

# ifdef SENTRY_CRASH_MANAGED_RUNTIME
static void
clearIgnoreSignal(void *value)
{
SentryCrashIgnoreSignal *entry = value;
atomic_store_explicit(&entry->signum, 0, memory_order_relaxed);
atomic_store_explicit(&entry->tid, 0, memory_order_relaxed);
}
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static void
createIgnoreSignalKey(void)
{
pthread_key_create(&g_ignoreSignalKey, clearIgnoreSignal);
}
# endif

// ============================================================================
# pragma mark - Callbacks -
// ============================================================================
Expand All @@ -102,17 +135,23 @@ restorePreviousSignalHandler(int sigNum)
static void
handleSignal(int sigNum, siginfo_t *signalInfo, void *userContext)
{
bool ignoreSignal = false;
# ifdef SENTRY_CRASH_MANAGED_RUNTIME
const int ignoreSignum = tl_ignoreSignum;
tl_ignoreSignum = 0;
const uintptr_t tid = (uintptr_t)pthread_self();
SentryCrashIgnoreSignal *entry = atomic_load_explicit(&g_ignoreSignals, memory_order_acquire);
while (entry != NULL) {
if (atomic_load_explicit(&entry->tid, memory_order_relaxed) == tid) {
if (atomic_exchange_explicit(&entry->signum, 0, memory_order_relaxed) == sigNum) {
ignoreSignal = true;
}
break;
}
entry = entry->next;
}
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# endif

SENTRY_ASYNC_SAFE_LOG_DEBUG("Trapped signal %d", sigNum);
if (g_isEnabled
# ifdef SENTRY_CRASH_MANAGED_RUNTIME
&& sigNum != ignoreSignum
# endif
) {
if (g_isEnabled && !ignoreSignal) {
thread_act_array_t threads = NULL;
mach_msg_type_number_t numThreads = 0;
// Signal handlers preempt the crashing thread, so reentrancy can
Expand Down Expand Up @@ -141,11 +180,7 @@ handleSignal(int sigNum, siginfo_t *signalInfo, void *userContext)
}

SENTRY_ASYNC_SAFE_LOG_DEBUG("Re-raising signal for regular handlers to catch.");
if (!g_isEnabled
# ifdef SENTRY_CRASH_MANAGED_RUNTIME
|| sigNum == ignoreSignum
# endif
) {
if (!g_isEnabled || ignoreSignal) {
// Avoid re-entering this handler on raise().
restorePreviousSignalHandler(sigNum);
}
Expand Down Expand Up @@ -339,7 +374,28 @@ void
sentrycrashcm_signal_ignore_next(int signum)
{
#if SENTRY_HAS_SIGNAL && defined(SENTRY_CRASH_MANAGED_RUNTIME)
tl_ignoreSignum = signum;
pthread_once(&g_ignoreSignalKeyOnce, createIgnoreSignalKey);

SentryCrashIgnoreSignal *entry = pthread_getspecific(g_ignoreSignalKey);
if (entry != NULL) {
atomic_store_explicit(&entry->signum, signum, memory_order_relaxed);
return;
}

entry = calloc(1, sizeof(*entry));
if (entry == NULL || pthread_setspecific(g_ignoreSignalKey, entry) != 0) {
free(entry);
return;
}

atomic_store_explicit(&entry->signum, signum, memory_order_relaxed);
atomic_store_explicit(&entry->tid, (uintptr_t)pthread_self(), memory_order_relaxed);

SentryCrashIgnoreSignal *head = atomic_load_explicit(&g_ignoreSignals, memory_order_relaxed);
do {
entry->next = head;
} while (!atomic_compare_exchange_weak_explicit(
&g_ignoreSignals, &head, entry, memory_order_release, memory_order_relaxed));
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Outdated
#else
(void)signum;
#endif
Expand Down
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