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

1 files changed, 12 insertions, 11 deletions

diff --git a/debuggerd/utility.c b/debuggerd/utility.c
index c0fb13a..64e5980 100644
--- a/debuggerd/utility.c
+++ b/debuggerd/utility.c
@@ -57,8 +57,8 @@ bool signal_has_address(int sig) {
     }
 }
 
-static void dump_backtrace(ptrace_context_t* context __attribute((unused)),
-        int tfd, int pid __attribute((unused)), bool at_fault,
+static void dump_backtrace(const ptrace_context_t* context __attribute((unused)),
+        int tfd, pid_t tid __attribute((unused)), bool at_fault,
         const backtrace_frame_t* backtrace, size_t frames) {
     _LOG(tfd, !at_fault, "\nbacktrace:\n");
 
@@ -66,7 +66,7 @@ static void dump_backtrace(ptrace_context_t* context __attribute((unused)),
     get_backtrace_symbols_ptrace(context, backtrace, frames, backtrace_symbols);
     for (size_t i = 0; i < frames; i++) {
         const backtrace_symbol_t* symbol = &backtrace_symbols[i];
-        const char* map_name = symbol->map_info ? symbol->map_info->name : "<unknown>";
+        const char* map_name = symbol->map_name ? symbol->map_name : "<unknown>";
         const char* symbol_name = symbol->demangled_name ? symbol->demangled_name : symbol->name;
         if (symbol_name) {
             _LOG(tfd, !at_fault, "    #%02d  pc %08x  %s (%s)\n",
@@ -79,11 +79,11 @@ static void dump_backtrace(ptrace_context_t* context __attribute((unused)),
     free_backtrace_symbols(backtrace_symbols, frames);
 }
 
-static void dump_stack_segment(ptrace_context_t* context, int tfd, int pid,
+static void dump_stack_segment(const ptrace_context_t* context, int tfd, pid_t tid,
         bool only_in_tombstone, uintptr_t* sp, size_t words, int label) {
     for (size_t i = 0; i < words; i++) {
         uint32_t stack_content;
-        if (!try_get_word(pid, *sp, &stack_content)) {
+        if (!try_get_word_ptrace(tid, *sp, &stack_content)) {
             break;
         }
 
@@ -116,7 +116,7 @@ static void dump_stack_segment(ptrace_context_t* context, int tfd, int pid,
     }
 }
 
-static void dump_stack(ptrace_context_t* context, int tfd, int pid, bool at_fault,
+static void dump_stack(const ptrace_context_t* context, int tfd, pid_t tid, bool at_fault,
         const backtrace_frame_t* backtrace, size_t frames) {
     bool have_first = false;
     size_t first, last;
@@ -138,7 +138,7 @@ static void dump_stack(ptrace_context_t* context, int tfd, int pid, bool at_faul
     // Dump a few words before the first frame.
     bool only_in_tombstone = !at_fault;
     uintptr_t sp = backtrace[first].stack_top - STACK_WORDS * sizeof(uint32_t);
-    dump_stack_segment(context, tfd, pid, only_in_tombstone, &sp, STACK_WORDS, -1);
+    dump_stack_segment(context, tfd, tid, only_in_tombstone, &sp, STACK_WORDS, -1);
 
     // Dump a few words from all successive frames.
     // Only log the first 3 frames, put the rest in the tombstone.
@@ -152,7 +152,7 @@ static void dump_stack(ptrace_context_t* context, int tfd, int pid, bool at_faul
             only_in_tombstone = true;
         }
         if (i == last) {
-            dump_stack_segment(context, tfd, pid, only_in_tombstone, &sp, STACK_WORDS, i);
+            dump_stack_segment(context, tfd, tid, only_in_tombstone, &sp, STACK_WORDS, i);
             if (sp < frame->stack_top + frame->stack_size) {
                 _LOG(tfd, only_in_tombstone, "         ........  ........\n");
             }
@@ -163,12 +163,13 @@ static void dump_stack(ptrace_context_t* context, int tfd, int pid, bool at_faul
             } else if (words > STACK_WORDS) {
                 words = STACK_WORDS;
             }
-            dump_stack_segment(context, tfd, pid, only_in_tombstone, &sp, words, i);
+            dump_stack_segment(context, tfd, tid, only_in_tombstone, &sp, words, i);
         }
     }
 }
 
-void dump_backtrace_and_stack(ptrace_context_t* context, int tfd, pid_t tid, bool at_fault) {
+void dump_backtrace_and_stack(const ptrace_context_t* context, int tfd, pid_t tid,
+        bool at_fault) {
     backtrace_frame_t backtrace[STACK_DEPTH];
     ssize_t frames = unwind_backtrace_ptrace(tid, context, backtrace, 0, STACK_DEPTH);
     if (frames > 0) {
@@ -237,7 +238,7 @@ void dump_memory(int tfd, pid_t tid, uintptr_t addr, bool at_fault) {
     }
 }
 
-void dump_nearby_maps(ptrace_context_t* context, int tfd, pid_t tid) {
+void dump_nearby_maps(const ptrace_context_t* context, int tfd, pid_t tid) {
     siginfo_t si;
     memset(&si, 0, sizeof(si));
     if (ptrace(PTRACE_GETSIGINFO, tid, 0, &si)) {