Don't collect useless stack frames; do demangle C++ symbols.
Previously, we'd collect every stack frame and then throw some away
when we came to log them. This meant that stack traces were effectively
shorter than the buffers that had been allocated for them. This patch
only stores frames we'll actually output.
Also dynamically call the C++ demangler so we don't have to try to
read mangled names. Because no one knows the mangling of operator new[]
for int arrays off the top of their head.
Bug: 7291287
Change-Id: I42b022fd7cd61675d05171de4c3b2704d058ef2a
diff --git a/libc/bionic/debug_stacktrace.cpp b/libc/bionic/debug_stacktrace.cpp
index 5c82205..9d53ad2 100644
--- a/libc/bionic/debug_stacktrace.cpp
+++ b/libc/bionic/debug_stacktrace.cpp
@@ -44,69 +44,102 @@
typedef _Unwind_Context __unwind_context;
#endif
+static mapinfo_t* gMapInfo = NULL;
+static void* gDemangler;
+typedef char* (*DemanglerFn)(const char*, char*, size_t*, int*);
+static DemanglerFn gDemanglerFn = NULL;
+
+__LIBC_HIDDEN__ void backtrace_startup() {
+ gMapInfo = mapinfo_create(getpid());
+ gDemangler = dlopen("libgccdemangle.so", RTLD_NOW);
+ if (gDemangler != NULL) {
+ void* sym = dlsym(gDemangler, "__cxa_demangle");
+ gDemanglerFn = reinterpret_cast<DemanglerFn>(sym);
+ }
+}
+
+__LIBC_HIDDEN__ void backtrace_shutdown() {
+ mapinfo_destroy(gMapInfo);
+ dlclose(gDemangler);
+}
+
+static char* demangle(const char* symbol) {
+ if (gDemanglerFn == NULL) {
+ return NULL;
+ }
+ return (*gDemanglerFn)(symbol, NULL, NULL, NULL);
+}
+
+struct stack_crawl_state_t {
+ uintptr_t* frames;
+ size_t frame_count;
+ size_t max_depth;
+ bool have_skipped_self;
+
+ stack_crawl_state_t(uintptr_t* frames, size_t max_depth)
+ : frames(frames), frame_count(0), max_depth(max_depth), have_skipped_self(false) {
+ }
+};
+
static _Unwind_Reason_Code trace_function(__unwind_context* context, void* arg) {
stack_crawl_state_t* state = static_cast<stack_crawl_state_t*>(arg);
- if (state->count) {
- uintptr_t ip = _Unwind_GetIP(context);
- if (ip) {
- state->addrs[0] = ip;
- state->addrs++;
- state->count--;
- return _URC_NO_REASON;
- }
+
+ uintptr_t ip = _Unwind_GetIP(context);
+
+ // The first stack frame is get_backtrace itself. Skip it.
+ if (ip != 0 && !state->have_skipped_self) {
+ state->have_skipped_self = true;
+ return _URC_NO_REASON;
}
- // If we run out of space to record the address or 0 has been seen, stop
- // unwinding the stack.
- return _URC_END_OF_STACK;
+
+ state->frames[state->frame_count++] = ip;
+ return (state->frame_count >= state->max_depth) ? _URC_END_OF_STACK : _URC_NO_REASON;
}
-__LIBC_HIDDEN__ int get_backtrace(uintptr_t* addrs, size_t max_entries) {
- stack_crawl_state_t state;
- state.count = max_entries;
- state.addrs = addrs;
+__LIBC_HIDDEN__ int get_backtrace(uintptr_t* frames, size_t max_depth) {
+ stack_crawl_state_t state(frames, max_depth);
_Unwind_Backtrace(trace_function, &state);
- return max_entries - state.count;
+ return state.frame_count;
}
-__LIBC_HIDDEN__ void log_backtrace(mapinfo_t* map_info, uintptr_t* addrs, size_t c) {
+__LIBC_HIDDEN__ void log_backtrace(uintptr_t* frames, size_t frame_count) {
uintptr_t self_bt[16];
- if (addrs == NULL) {
- c = get_backtrace(self_bt, 16);
- addrs = self_bt;
+ if (frames == NULL) {
+ frame_count = get_backtrace(self_bt, 16);
+ frames = self_bt;
}
__libc_format_log(ANDROID_LOG_ERROR, "libc",
"*** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***\n");
- int index = 0;
- for (size_t i = 0 ; i < c; ++i) {
+ for (size_t i = 0 ; i < frame_count; ++i) {
void* offset = 0;
const char* symbol = NULL;
Dl_info info;
- if (dladdr((void*) addrs[i], &info) != 0) {
+ if (dladdr((void*) frames[i], &info) != 0) {
offset = info.dli_saddr;
symbol = info.dli_sname;
}
- // This test is a bit sketchy, but it allows us to skip the
- // stack trace entries due to this debugging code. it works
- // because those don't have a symbol (they're not exported).
- if (symbol != NULL || index > 0) {
- unsigned int rel_pc;
- const mapinfo_t* mi = mapinfo_find(map_info, addrs[i], &rel_pc);
- const char* soname = mi ? mi->name : info.dli_fname;
- if (soname == NULL) {
- soname = "unknown";
- }
- if (symbol) {
- __libc_format_log(ANDROID_LOG_ERROR, "libc", " #%02d pc %08x %s (%s+0x%x)",
- index, rel_pc, soname, symbol, addrs[i] - (uintptr_t) offset);
- } else {
- __libc_format_log(ANDROID_LOG_ERROR, "libc", " #%02d pc %08x %s",
- index, rel_pc, soname);
- }
- ++index;
+ uintptr_t rel_pc;
+ const mapinfo_t* mi = (gMapInfo != NULL) ? mapinfo_find(gMapInfo, frames[i], &rel_pc) : NULL;
+ const char* soname = (mi != NULL) ? mi->name : info.dli_fname;
+ if (soname == NULL) {
+ soname = "<unknown>";
+ }
+ if (symbol != NULL) {
+ // TODO: we might need a flag to say whether it's safe to allocate (demangling allocates).
+ char* demangled_symbol = demangle(symbol);
+ const char* best_name = (demangled_symbol != NULL) ? demangled_symbol : symbol;
+
+ __libc_format_log(ANDROID_LOG_ERROR, "libc", " #%02d pc %08x %s (%s+0x%x)",
+ i, rel_pc, soname, best_name, frames[i] - (uintptr_t) offset);
+
+ free(demangled_symbol);
+ } else {
+ __libc_format_log(ANDROID_LOG_ERROR, "libc", " #%02d pc %08x %s",
+ i, rel_pc, soname);
}
}
}