From ec91809daeb35113bfc4840c07367ff24f75903a Mon Sep 17 00:00:00 2001
From: Josh Gao <jmgao@google.com>
Date: Fri, 10 Mar 2017 14:44:54 -0800
Subject: [PATCH 1/2] debuggerd_handler: restore errno.

Bug: http://b/31448909
Test: mma
Change-Id: I737d66e8bed5fb31c2558f68608d3df460fa73c9
---
 debuggerd/handler/debuggerd_handler.cpp | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/debuggerd/handler/debuggerd_handler.cpp b/debuggerd/handler/debuggerd_handler.cpp
index c09c2f31f..cf24d5767 100644
--- a/debuggerd/handler/debuggerd_handler.cpp
+++ b/debuggerd/handler/debuggerd_handler.cpp
@@ -62,6 +62,19 @@
 
 #define CRASH_DUMP_PATH "/system/bin/" CRASH_DUMP_NAME
 
+class ErrnoRestorer {
+ public:
+  ErrnoRestorer() : saved_errno_(errno) {
+  }
+
+  ~ErrnoRestorer() {
+    errno = saved_errno_;
+  }
+
+ private:
+  int saved_errno_;
+};
+
 extern "C" void debuggerd_fallback_handler(siginfo_t*, ucontext_t*, void*);
 
 static debuggerd_callbacks_t g_callbacks;
@@ -328,6 +341,10 @@ static void resend_signal(siginfo_t* info, bool crash_dump_started) {
 // Handler that does crash dumping by forking and doing the processing in the child.
 // Do this by ptracing the relevant thread, and then execing debuggerd to do the actual dump.
 static void debuggerd_signal_handler(int signal_number, siginfo_t* info, void* context) {
+  // Make sure we don't change the value of errno, in case a signal comes in between the process
+  // making a syscall and checking errno.
+  ErrnoRestorer restorer;
+
   // It's possible somebody cleared the SA_SIGINFO flag, which would mean
   // our "info" arg holds an undefined value.
   if (!have_siginfo(signal_number)) {

From 428daafc5b9a2186e2d893c8ebd1c4337ce3c7a9 Mon Sep 17 00:00:00 2001
From: Josh Gao <jmgao@google.com>
Date: Fri, 10 Mar 2017 14:49:19 -0800
Subject: [PATCH 2/2] crash_dump: improve logging for when a process dies
 prematurely.

If a process that's getting dumped dies before crash_dump starts (e.g.
because seccomp immediately kills it after it execs crash_dump),
improve the error message to not just say "target died before we could
attach".

Bug: http://b/36077710
Test: inserted an exit in the handler, inspected output
Change-Id: I7d394c66d60d328b096b15654b3648e1ed711728
---
 debuggerd/crash_dump.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/debuggerd/crash_dump.cpp b/debuggerd/crash_dump.cpp
index 65854247e..57a6c448a 100644
--- a/debuggerd/crash_dump.cpp
+++ b/debuggerd/crash_dump.cpp
@@ -148,7 +148,12 @@ static void abort_handler(pid_t target, const bool& tombstoned_connected,
     }
   }
 
-  dprintf(output_fd.get(), "crash_dump failed to dump process %d: %s\n", target, abort_msg);
+  dprintf(output_fd.get(), "crash_dump failed to dump process");
+  if (target != 1) {
+    dprintf(output_fd.get(), " %d: %s\n", target, abort_msg);
+  } else {
+    dprintf(output_fd.get(), ": %s\n", abort_msg);
+  }
 
   _exit(1);
 }
@@ -195,7 +200,7 @@ int main(int argc, char** argv) {
   pid_t pseudothread_tid;
 
   if (target == 1) {
-    LOG(FATAL) << "target died before we could attach";
+    LOG(FATAL) << "target died before we could attach (received main tid = " << main_tid << ")";
   }
 
   if (!android::base::ParseInt(argv[1], &main_tid, 1, std::numeric_limits<pid_t>::max())) {