feat(native): symbolicated stacktraces for non-crashed threads on Linux

CHANGELOG.md

@@ -4,6 +4,7 @@
 
 **Features**:
 
+- Native/Linux: symbolicate stack frames in the crash daemon. ([#1747](https://github.com/getsentry/sentry-native/pull/1747))
 - Native: add opt-in async crash upload mode so crashed apps can exit early after crash data is captured, while the crash daemon finishes potentially large uploads in the background. ([#1739](https://github.com/getsentry/sentry-native/pull/1739))
 - Add a `transfer_timeout` option for SDK-managed HTTP transports. ([#1741](https://github.com/getsentry/sentry-native/pull/1741))
 

CMakeLists.txt

@@ -686,6 +686,10 @@ if(SENTRY_WITH_LIBUNWIND)
 			endif()
 		else()
 			# Use vendored libunwind
+			if(SENTRY_BACKEND_NATIVE)
+				# Build remote unwinding support for the native backend's crash daemon
+				set(LIBUNWIND_BUILD_REMOTE TRUE)
+			endif()
 			add_subdirectory(vendor/libunwind)
 			target_link_libraries(sentry PRIVATE unwind)
 			if(NOT SENTRY_BUILD_SHARED_LIBS)
@@ -851,6 +855,10 @@ elseif(SENTRY_BACKEND_NATIVE)
 		SENTRY_BUILD_STATIC
 	)
 
+	if(SENTRY_WITH_LIBUNWIND AND LINUX)
+		target_compile_definitions(sentry-crash PRIVATE SENTRY_WITH_UNWINDER_LIBUNWIND_REMOTE)
+	endif()
+
 	# Copy include directories from sentry target
 	target_include_directories(sentry-crash PRIVATE
 		${PROJECT_SOURCE_DIR}/include
@@ -891,9 +899,12 @@ elseif(SENTRY_BACKEND_NATIVE)
 
 	if(SENTRY_WITH_LIBUNWIND AND LINUX)
 		if(SENTRY_LIBUNWIND_SYSTEM)
-			target_link_libraries(sentry-crash PRIVATE PkgConfig::LIBUNWIND)
+			pkg_check_modules(LIBUNWIND_PTRACE REQUIRED IMPORTED_TARGET libunwind-ptrace)
+			target_link_libraries(sentry-crash PRIVATE PkgConfig::LIBUNWIND PkgConfig::LIBUNWIND_PTRACE)
 		else()
-			target_link_libraries(sentry-crash PRIVATE unwind)
+			# Use unwind_remote for the daemon (includes ptrace accessors
+			# for remote DWARF unwinding of the crashed process)
+			target_link_libraries(sentry-crash PRIVATE unwind_remote)
 		endif()
 	endif()
 

src/CMakeLists.txt

@@ -171,6 +171,13 @@ elseif(SENTRY_BACKEND_NATIVE)
 		backends/native/minidump/sentry_minidump_writer.h
 	)
 
+	# Remote unwinding (Linux only — uses libunwind ptrace accessors)
+	if(LINUX)
+		sentry_target_sources_cwd(sentry
+			unwinder/sentry_unwinder_libunwind_remote.c
+		)
+	endif()
+
 	# Platform-specific minidump writers
 	if(LINUX OR ANDROID)
 		sentry_target_sources_cwd(sentry

src/backends/native/sentry_crash_daemon.c

@@ -47,6 +47,9 @@
 #        include <mach-o/dyld.h>
 #        include <spawn.h>
 #    endif
+#    if defined(SENTRY_PLATFORM_LINUX)
+#        include "unwinder/sentry_unwinder.h"
+#    endif
 #elif defined(SENTRY_PLATFORM_WINDOWS)
 #    include <dbghelp.h>
 #    include <fcntl.h>
@@ -544,6 +547,24 @@ build_registers_from_ctx(const sentry_crash_context_t *ctx, size_t thread_idx)
     return registers;
 }
 
+#if defined(SENTRY_PLATFORM_LINUX)
+static sentry_value_t
+build_registers_from_remote_registers(
+    const sentry_remote_registers_t *remote_registers)
+{
+    sentry_value_t registers = sentry_value_new_object();
+
+    for (size_t i = 0; i < remote_registers->count; i++) {
+        const sentry_remote_register_t *remote_register
+            = &remote_registers->values[i];
+        sentry_value_set_by_key(registers, remote_register->name,
+            sentry__value_new_addr(remote_register->value));
+    }
+
+    return registers;
+}
+#endif
+
 /**
  * Maximum number of frames to unwind
  */
@@ -905,10 +926,88 @@ build_stacktrace_for_thread(
     sentry_value_t temp_frames[MAX_STACK_FRAMES];
     int frame_count = 0;
 
+#if defined(SENTRY_PLATFORM_LINUX)
+    // Remote DWARF unwinding via libunwind ptrace accessors. Do not attach to
+    // the crashed thread from the daemon; use the saved fault context below.
+    {
+        pid_t tid = 0;
+        if (thread_idx == SIZE_MAX) {
+            tid = ctx->crashed_tid;
+        } else if (thread_idx < ctx->platform.num_threads) {
+            tid = ctx->platform.threads[thread_idx].tid;
+        }
+
+        bool is_crashed_thread
+            = thread_idx == SIZE_MAX || tid == ctx->crashed_tid;
+
+        if (tid > 0 && !is_crashed_thread) {
+            sentry_remote_registers_t registers = { 0 };
+            sentry_remote_frame_t *remote_frames
+                = sentry_malloc(sizeof(*remote_frames) * MAX_STACK_FRAMES);
+            size_t remote_count = remote_frames
+                ? sentry__unwind_stack_from_thread(
+                      tid, remote_frames, MAX_STACK_FRAMES, &registers)
+                : 0;
+
+            if (remote_count > 0) {
+                SENTRY_DEBUGF("Remote unwound %zu frames for thread %d",
+                    remote_count, tid);
+
+                for (size_t i = 0;
+                    i < remote_count && frame_count < MAX_STACK_FRAMES; i++) {
+                    if (remote_frames[i].ip == 0
+                        || !is_valid_code_addr(remote_frames[i].ip)) {
+                        continue;
+                    }
+                    temp_frames[frame_count] = sentry_value_new_object();
+                    sentry_value_set_by_key(temp_frames[frame_count],
+                        "instruction_addr",
+                        sentry__value_new_addr(remote_frames[i].ip));
+                    // Trust describes the unwind source, not the emitted
+                    // frame index. If the initial cursor frame is filtered
+                    // out, the next emitted frame was still reached via CFI.
+                    sentry_value_set_by_key(temp_frames[frame_count], "trust",
+                        sentry_value_new_string(i == 0 ? "context" : "cfi"));
+                    enrich_frame_with_module_info(
+                        ctx, temp_frames[frame_count], remote_frames[i].ip);
+                    if (remote_frames[i].symbol[0]) {
+                        sentry_value_set_by_key(temp_frames[frame_count],
+                            "function",
+                            sentry_value_new_string(remote_frames[i].symbol));
+                    }
+                    frame_count++;
+                }
+
+                if (frame_count > 0) {
+                    if (stack_buf) {
+                        sentry_free(stack_buf);
+                    }
+
+                    for (int i = frame_count - 1; i >= 0; i--) {
+                        sentry_value_append(frames, temp_frames[i]);
+                    }
+                    sentry_value_set_by_key(stacktrace, "frames", frames);
+                    if (registers.count > 0) {
+                        sentry_value_set_by_key(stacktrace, "registers",
+                            build_registers_from_remote_registers(&registers));
+                    }
+                    sentry_free(remote_frames);
+                    return stacktrace;
+                }
+            }
+
+            if (remote_frames) {
+                sentry_free(remote_frames);
+            }
+        }
+    }
+    // Fall through to pre-captured backtrace or FP-walking if remote
+    // unwinding failed
+#endif
+
 #if defined(SENTRY_PLATFORM_LINUX) || defined(SENTRY_PLATFORM_ANDROID)
-    // Use pre-captured libunwind backtrace if available (DWARF-based, works
-    // without frame pointers). This is preferred over FP-based walking for
-    // the crashed thread.
+    // Fallback: use pre-captured libunwind backtrace if available
+    // (DWARF-based, works without frame pointers).
     if (ctx->platform.backtrace_count > 0
         && (thread_idx == SIZE_MAX || thread_idx == 0)) {
         SENTRY_DEBUGF("Using pre-captured libunwind backtrace (%zu frames)",
@@ -924,6 +1023,9 @@ build_stacktrace_for_thread(
             temp_frames[frame_count] = sentry_value_new_object();
             sentry_value_set_by_key(temp_frames[frame_count],
                 "instruction_addr", sentry__value_new_addr(frame_ip));
+            // Trust describes the unwind source, not the emitted frame index.
+            // If the initial cursor frame is filtered out, the next emitted
+            // frame was still reached via CFI.
             sentry_value_set_by_key(temp_frames[frame_count], "trust",
                 sentry_value_new_string(i == 0 ? "context" : "cfi"));
             enrich_frame_with_module_info(

src/unwinder/sentry_unwinder.c

@@ -1,3 +1,4 @@
+#include "sentry_unwinder.h"
 #include "sentry_boot.h"
 
 #define DEFINE_UNWINDER(Func)                                                  \
@@ -19,6 +20,24 @@ DEFINE_UNWINDER(libunwind);
 DEFINE_UNWINDER(libunwind_mac);
 DEFINE_UNWINDER(psunwind);
 
+#if defined(SENTRY_PLATFORM_LINUX)
+#    define DEFINE_THREAD_UNWINDER(Func)                                       \
+        size_t sentry__unwind_stack_from_thread_##Func(pid_t tid,              \
+            sentry_remote_frame_t *frames, size_t max_frames,                  \
+            sentry_remote_registers_t *registers)
+
+#    define TRY_THREAD_UNWINDER(Func)                                          \
+        do {                                                                   \
+            size_t rv = sentry__unwind_stack_from_thread_##Func(               \
+                tid, frames, max_frames, registers);                           \
+            if (rv > 0) {                                                      \
+                return rv;                                                     \
+            }                                                                  \
+        } while (0)
+
+DEFINE_THREAD_UNWINDER(libunwind_remote);
+#endif
+
 static size_t
 unwind_stack(
     void *addr, const sentry_ucontext_t *uctx, void **ptrs, size_t max_frames)
@@ -56,3 +75,19 @@ sentry_unwind_stack_from_ucontext(
 {
     return unwind_stack(NULL, uctx, stacktrace_out, max_len);
 }
+
+#if defined(SENTRY_PLATFORM_LINUX)
+size_t
+sentry__unwind_stack_from_thread(pid_t tid, sentry_remote_frame_t *frames,
+    size_t max_frames, sentry_remote_registers_t *registers)
+{
+    (void)tid;
+    (void)frames;
+    (void)max_frames;
+    (void)registers;
+#    ifdef SENTRY_WITH_UNWINDER_LIBUNWIND_REMOTE
+    TRY_THREAD_UNWINDER(libunwind_remote);
+#    endif
+    return 0;
+}
+#endif

src/unwinder/sentry_unwinder.h

@@ -1,8 +1,43 @@
 #ifndef SENTRY_UNWINDER_H_INCLUDED
 #define SENTRY_UNWINDER_H_INCLUDED
 
+#include "sentry_boot.h"
+
+#include <stdint.h>
+
 typedef struct {
     uintptr_t lo, hi;
 } mem_range_t;
 
+#if defined(SENTRY_PLATFORM_LINUX)
+
+#    include <stddef.h>
+#    include <sys/types.h>
+
+#    define SENTRY_REMOTE_UNWIND_MAX_REGISTER_NAME 16
+#    define SENTRY_REMOTE_UNWIND_MAX_REGISTERS 64
+#    define SENTRY_REMOTE_UNWIND_MAX_SYMBOL 256
+
+typedef struct {
+    char name[SENTRY_REMOTE_UNWIND_MAX_REGISTER_NAME];
+    uint64_t value;
+} sentry_remote_register_t;
+
+typedef struct {
+    uint64_t ip;
+    char symbol[SENTRY_REMOTE_UNWIND_MAX_SYMBOL];
+    uint64_t symbol_offset;
+} sentry_remote_frame_t;
+
+typedef struct {
+    size_t count;
+    sentry_remote_register_t values[SENTRY_REMOTE_UNWIND_MAX_REGISTERS];
+} sentry_remote_registers_t;
+
+size_t sentry__unwind_stack_from_thread(pid_t tid,
+    sentry_remote_frame_t *frames, size_t max_frames,
+    sentry_remote_registers_t *registers);
+
+#endif
+
 #endif // SENTRY_UNWINDER_H_INCLUDED