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/arch-x86/backtrace-x86.c b/libcorkscrew/arch-x86/backtrace-x86.c
index 1324899..24fadcb 100644
--- a/libcorkscrew/arch-x86/backtrace-x86.c
+++ b/libcorkscrew/arch-x86/backtrace-x86.c
@@ -73,14 +73,21 @@
uint32_t esp;
} unwind_state_t;
-static ssize_t unwind_backtrace_common(pid_t tid, const ptrace_context_t* context,
+uintptr_t rewind_pc_arch(const memory_t* memory, uintptr_t pc) {
+ // TODO: Implement for x86.
+ return pc;
+}
+
+static ssize_t unwind_backtrace_common(const memory_t* memory,
+ const map_info_t* map_info_list,
unwind_state_t* state, backtrace_frame_t* backtrace,
size_t ignore_depth, size_t max_depth) {
size_t ignored_frames = 0;
size_t returned_frames = 0;
- while (state->ebp && returned_frames < max_depth) {
- backtrace_frame_t* frame = add_backtrace_entry(state->eip,
+ for (size_t index = 0; state->ebp && returned_frames < max_depth; index++) {
+ backtrace_frame_t* frame = add_backtrace_entry(
+ index ? rewind_pc_arch(memory, state->eip) : state->eip,
backtrace, ignore_depth, max_depth,
&ignored_frames, &returned_frames);
uint32_t next_esp = state->ebp + 8;
@@ -91,8 +98,8 @@
}
}
state->esp = next_esp;
- if (!try_get_word(tid, state->ebp + 4, &state->eip)
- || !try_get_word(tid, state->ebp, &state->ebp)
+ if (!try_get_word(memory, state->ebp + 4, &state->eip)
+ || !try_get_word(memory, state->ebp, &state->ebp)
|| !state->eip) {
break;
}
@@ -102,6 +109,7 @@
}
ssize_t unwind_backtrace_signal_arch(siginfo_t* siginfo, void* sigcontext,
+ const map_info_t* map_info_list,
backtrace_frame_t* backtrace, size_t ignore_depth, size_t max_depth) {
const ucontext_t* uc = (const ucontext_t*)sigcontext;
@@ -110,7 +118,10 @@
state.eip = uc->uc_mcontext.eip;
state.esp = uc->uc_mcontext.esp;
- return unwind_backtrace_common(-1, NULL, &state, backtrace, ignore_depth, max_depth);
+ memory_t memory;
+ init_memory(&memory, map_info_list);
+ return unwind_backtrace_common(&memory, map_info_list,
+ &state, backtrace, ignore_depth, max_depth);
}
ssize_t unwind_backtrace_ptrace_arch(pid_t tid, const ptrace_context_t* context,
@@ -125,5 +136,8 @@
state.eip = regs.eip;
state.esp = regs.esp;
- return unwind_backtrace_common(tid, context, &state, backtrace, ignore_depth, max_depth);
+ memory_t memory;
+ init_memory_ptrace(&memory, tid);
+ return unwind_backtrace_common(&memory, context->map_info_list,
+ &state, backtrace, ignore_depth, max_depth);
}