Fix multithreaded backtraces for seccomp processes.

Add threads to the existing seccomp backtrace test to prevent
regressing this.

Bug: http://b/114139908
Bug: http://b/115349586
Test: debuggerd_test32
Test: debuggerd_test64
Change-Id: I07fbe1619b60f0008deb045a249f9045404478c2

1 files changed, 9 insertions, 4 deletions

diff --git a/debuggerd/handler/debuggerd_handler.cpp b/debuggerd/handler/debuggerd_handler.cpp
index 15557b6d8..a064ca0f7 100644
--- a/debuggerd/handler/debuggerd_handler.cpp
+++ b/debuggerd/handler/debuggerd_handler.cpp
@@ -58,6 +58,8 @@
 #include "dump_type.h"
 #include "protocol.h"
 
+#include "handler/fallback.h"
+
 using android::base::Pipe;
 
 // We muck with our fds in a 'thread' that doesn't share the same fd table.
@@ -473,13 +475,15 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* c
   }
 
   void* abort_message = nullptr;
+  uintptr_t si_val = reinterpret_cast<uintptr_t>(info->si_ptr);
   if (signal_number == DEBUGGER_SIGNAL) {
     if (info->si_code == SI_QUEUE && info->si_pid == __getpid()) {
       // Allow for the abort message to be explicitly specified via the sigqueue value.
       // Keep the bottom bit intact for representing whether we want a backtrace or a tombstone.
-      uintptr_t value = reinterpret_cast<uintptr_t>(info->si_ptr);
-      abort_message = reinterpret_cast<void*>(value & ~1);
-      info->si_ptr = reinterpret_cast<void*>(value & 1);
+      if (si_val != kDebuggerdFallbackSivalUintptrRequestDump) {
+        abort_message = reinterpret_cast<void*>(si_val & ~1);
+        info->si_ptr = reinterpret_cast<void*>(si_val & 1);
+      }
     }
   } else {
     if (g_callbacks.get_abort_message) {
@@ -492,7 +496,8 @@ static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* c
   // of a specific thread. It is possible that the prctl call might return 1,
   // then return 0 in subsequent calls, so check the sival_int to determine if
   // the fallback handler should be called first.
-  if (info->si_value.sival_int == ~0 || prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0) == 1) {
+  if (si_val == kDebuggerdFallbackSivalUintptrRequestDump ||
+      prctl(PR_GET_NO_NEW_PRIVS, 0, 0, 0, 0) == 1) {
     // This check might be racy if another thread sets NO_NEW_PRIVS, but this should be unlikely,
     // you can only set NO_NEW_PRIVS to 1, and the effect should be at worst a single missing
     // ANR trace.