Improve stack unwinder robustness.
Keep track of whether memory maps are readable. Use the information
in try_get_word to try to avoid accidentally dereferencing an invalid
pointer within the current process. (Note that I haven't ever
seen that happen during normal unwinding, but it pays to be
a little more careful.)
Refactored try_get_word a little to make it easier to pass it the
needed state for validation checks by way of a little memory_t struct.
Improved how the memory map for the current process is cached. This is
important because we need up to date information about readable maps.
Use a 5 second cache expiration.
Improved the PC -> LR fallback logic in the unwinder so we can
eke out an extra frame sometimes.
Fixed a bug reading ELF program headers. The phnum & phentsize
fields are half-words. We were incorrectly interpreting
phnum as a whole word.
Used android_atomic_* operations carefully in the unwinder
to prevent possible memory races between the dumper and the dumpee.
This was highly unlikely (or even impossible due to the presence
of other barriers along the way) but the code is clearer now about
its invariants.
Fixed a bug in debuggerd where the pid was being passed to have
its stack dump taken instead of the tid, resulting in short
stacks because ptrace couldn't read the data if pid != tid.
Did a full sweep to ensure that we use pid / tid correctly everywhere.
Ported old code from debuggerd to rewind the program counter back
one instruction so that it points to the branch instruction itself
instead of the return address.
Change-Id: Icc4eb08320052975a4ae7f0f5f0ac9308a2d33d7
diff --git a/libcorkscrew/map_info.c b/libcorkscrew/map_info.c
index 60ed9b4..f33378f 100644
--- a/libcorkscrew/map_info.c
+++ b/libcorkscrew/map_info.c
@@ -26,6 +26,7 @@
#include <pthread.h>
#include <unistd.h>
#include <cutils/log.h>
+#include <sys/time.h>
// 6f000000-6f01e000 rwxp 00000000 00:0c 16389419 /system/lib/libcomposer.so\n
// 012345678901234567890123456789012345678901234567890123456789
@@ -54,10 +55,14 @@
if (mi) {
mi->start = start;
mi->end = end;
+ mi->is_readable = strlen(permissions) == 4 && permissions[0] == 'r';
mi->is_executable = strlen(permissions) == 4 && permissions[2] == 'x';
mi->data = NULL;
memcpy(mi->name, name, name_len);
mi->name[name_len] = '\0';
+ ALOGV("Parsed map: start=0x%08x, end=0x%08x, "
+ "is_readable=%d, is_executable=%d, name=%s",
+ mi->start, mi->end, mi->is_readable, mi->is_executable, mi->name);
}
return mi;
}
@@ -99,14 +104,87 @@
return mi;
}
-static pthread_once_t g_my_milist_once = PTHREAD_ONCE_INIT;
-static map_info_t* g_my_milist = NULL;
-
-static void init_my_milist_once() {
- g_my_milist = load_map_info_list(getpid());
+bool is_readable_map(const map_info_t* milist, uintptr_t addr) {
+ const map_info_t* mi = find_map_info(milist, addr);
+ return mi && mi->is_readable;
}
-const map_info_t* my_map_info_list() {
- pthread_once(&g_my_milist_once, init_my_milist_once);
- return g_my_milist;
+bool is_executable_map(const map_info_t* milist, uintptr_t addr) {
+ const map_info_t* mi = find_map_info(milist, addr);
+ return mi && mi->is_executable;
+}
+
+static pthread_mutex_t g_my_map_info_list_mutex = PTHREAD_MUTEX_INITIALIZER;
+static map_info_t* g_my_map_info_list = NULL;
+
+static const int64_t MAX_CACHE_AGE = 5 * 1000 * 1000000LL;
+
+typedef struct {
+ uint32_t refs;
+ int64_t timestamp;
+} my_map_info_data_t;
+
+static int64_t now() {
+ struct timespec t;
+ t.tv_sec = t.tv_nsec = 0;
+ clock_gettime(CLOCK_MONOTONIC, &t);
+ return t.tv_sec * 1000000000LL + t.tv_nsec;
+}
+
+static void dec_ref(map_info_t* milist, my_map_info_data_t* data) {
+ if (!--data->refs) {
+ ALOGV("Freed my_map_info_list %p.", milist);
+ free(data);
+ free_map_info_list(milist);
+ }
+}
+
+map_info_t* acquire_my_map_info_list() {
+ pthread_mutex_lock(&g_my_map_info_list_mutex);
+
+ int64_t time = now();
+ if (g_my_map_info_list) {
+ my_map_info_data_t* data = (my_map_info_data_t*)g_my_map_info_list->data;
+ int64_t age = time - data->timestamp;
+ if (age >= MAX_CACHE_AGE) {
+ ALOGV("Invalidated my_map_info_list %p, age=%lld.", g_my_map_info_list, age);
+ dec_ref(g_my_map_info_list, data);
+ g_my_map_info_list = NULL;
+ } else {
+ ALOGV("Reusing my_map_info_list %p, age=%lld.", g_my_map_info_list, age);
+ }
+ }
+
+ if (!g_my_map_info_list) {
+ my_map_info_data_t* data = (my_map_info_data_t*)malloc(sizeof(my_map_info_data_t));
+ g_my_map_info_list = load_map_info_list(getpid());
+ if (g_my_map_info_list) {
+ ALOGV("Loaded my_map_info_list %p.", g_my_map_info_list);
+ g_my_map_info_list->data = data;
+ data->refs = 1;
+ data->timestamp = time;
+ } else {
+ free(data);
+ }
+ }
+
+ map_info_t* milist = g_my_map_info_list;
+ if (milist) {
+ my_map_info_data_t* data = (my_map_info_data_t*)g_my_map_info_list->data;
+ data->refs += 1;
+ }
+
+ pthread_mutex_unlock(&g_my_map_info_list_mutex);
+ return milist;
+}
+
+void release_my_map_info_list(map_info_t* milist) {
+ if (milist) {
+ pthread_mutex_lock(&g_my_map_info_list_mutex);
+
+ my_map_info_data_t* data = (my_map_info_data_t*)milist->data;
+ dec_ref(milist, data);
+
+ pthread_mutex_unlock(&g_my_map_info_list_mutex);
+ }
}