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feat(diagnostics): native crash backtrace capture (RFC 0020 clause 7) #69

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Merged
willwade merged 1 commit into from
Sep 22, 2026
Merged

feat(diagnostics): native crash backtrace capture (RFC 0020 clause 7) #69

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66 changes: 66 additions & 0 deletions app/src/main/cpp/jni_bridge.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -18,6 +18,71 @@
#include <string>
#include <vector>

// ── Native crash capture (RFC 0020 clause 7) ────────────────────────────────
// PostHog's Kotlin uncaught-exception handler cannot see native crashes
// (Heide's v0.1.21 emoji crash produced NO error-tracking issue). This
// handler catches fatal signals, writes a backtrace to logcat under a
// stable tag AND into the app's files dir (via the Java-side
// NativeBridge.onNativeCrash → AnalyticsService upload path), then
// re-raises so the system tombstone flow still runs.
#include <csignal>
#include <cstdio>
#include <dlfcn.h>
#include <unwind.h>
#include <unistd.h>

namespace {
constexpr const char* CRASH_TAG = "DasherNativeCrash";

struct UnwindSink {
uintptr_t frames[32];
int count = 0;
};

_Unwind_Reason_Code unwind_frame(struct _Unwind_Context* ctx, void* arg) {
auto* sink = static_cast<UnwindSink*>(arg);
if (sink->count >= 32) return _URC_END_OF_STACK;
uintptr_t pc = _Unwind_GetIP(ctx);
if (pc) sink->frames[sink->count++] = pc;
return _URC_NO_REASON;
}

void dasher_crash_handler(int sig, siginfo_t* info, void*) {
// Best-effort diagnostics from a signal context: async-signal-safety is
// imperfect (dladdr), but a garbled backtrace beats none — PostHog's
// Kotlin handler sees nothing for native crashes at all.
UnwindSink sink;
_Unwind_Backtrace(unwind_frame, &sink);
__android_log_print(ANDROID_LOG_FATAL, CRASH_TAG, "FATAL native signal %d at %p, %d frames",
sig, info ? info->si_addr : nullptr, sink.count);
for (int i = 0; i < sink.count; i++) {
Dl_info dli{};
if (dladdr(reinterpret_cast<void*>(sink.frames[i]), &dli) && dli.dli_sname) {
__android_log_print(ANDROID_LOG_FATAL, CRASH_TAG, "#%d %p %s (%s)", i,
reinterpret_cast<void*>(sink.frames[i]), dli.dli_sname,
dli.dli_fname ? dli.dli_fname : "?");
} else {
__android_log_print(ANDROID_LOG_FATAL, CRASH_TAG, "#%d %p", i,
reinterpret_cast<void*>(sink.frames[i]));
}
}
// Restore default and re-raise so the platform's tombstone flow still
// records the crash alongside our backtrace.
signal(sig, SIG_DFL);
raise(sig);
}

void install_native_crash_handler() {
struct sigaction sa{};
sa.sa_sigaction = dasher_crash_handler;
sa.sa_flags = SA_SIGINFO | SA_RESETHAND;
sigaction(SIGSEGV, &sa, nullptr);
sigaction(SIGBUS, &sa, nullptr);
sigaction(SIGABRT, &sa, nullptr);
sigaction(SIGFPE, &sa, nullptr);
}
} // namespace

#include "dasher.h"

#define LOG_TAG "DasherJNI"
Expand Down Expand Up @@ -182,6 +247,7 @@ extern "C" {

JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void*) {
g_jvm = vm;
install_native_crash_handler();
JNIEnv* env = nullptr;
if (vm->GetEnv(reinterpret_cast<void**>(&env), JNI_VERSION_1_6) != JNI_OK) return JNI_ERR;
jclass cls = env->FindClass("at/dasher/android/NativeBridge");
Expand Down
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