Handle nested signals

This allows for signals to be raised inside the ART signal handler.
This can occur when the JavaStackTraceHandler attempts to generate
a stack trace and something goes wrong.

It also fixes an issue where the fault manager was not being
correctly shut down inside the signal chaining code.  In this
case the signal handler was not restored to the original.

Bug: 17006816
Bug: 17133266

(cherry picked from commit fabe91e0d558936ac26b98d2b4ee1af08f58831d)

Change-Id: I10730ef52d5d8d34610a5293253b3be6caf4829e

1 files changed, 13 insertions, 5 deletions

diff --git a/sigchainlib/sigchain.cc b/sigchainlib/sigchain.cc
index 2ba7405..c655226 100644
--- a/sigchainlib/sigchain.cc
+++ b/sigchainlib/sigchain.cc
@@ -45,8 +45,8 @@ class SignalAction {
 
   // Unclaim the signal and restore the old action.
   void Unclaim(int signal) {
-    sigaction(signal, &action_, NULL);        // Restore old action.
     claimed_ = false;
+    sigaction(signal, &action_, NULL);        // Restore old action.
   }
 
   // Get the action associated with this signal.
@@ -155,8 +155,12 @@ int sigaction(int signal, const struct sigaction* new_action, struct sigaction*
 
   void* linked_sigaction_sym = dlsym(RTLD_NEXT, "sigaction");
   if (linked_sigaction_sym == nullptr) {
-    log("Unable to find next sigaction in signal chain");
-    abort();
+    linked_sigaction_sym = dlsym(RTLD_DEFAULT, "sigaction");
+    if (linked_sigaction_sym == nullptr ||
+        linked_sigaction_sym == reinterpret_cast<void*>(sigaction)) {
+      log("Unable to find next sigaction in signal chain");
+      abort();
+    }
   }
 
   typedef int (*SigAction)(int, const struct sigaction*, struct sigaction*);
@@ -184,8 +188,12 @@ int sigprocmask(int how, const sigset_t* bionic_new_set, sigset_t* bionic_old_se
 
   void* linked_sigprocmask_sym = dlsym(RTLD_NEXT, "sigprocmask");
   if (linked_sigprocmask_sym == nullptr) {
-    log("Unable to find next sigprocmask in signal chain");
-    abort();
+    linked_sigprocmask_sym = dlsym(RTLD_DEFAULT, "sigprocmask");
+    if (linked_sigprocmask_sym == nullptr ||
+        linked_sigprocmask_sym == reinterpret_cast<void*>(sigprocmask)) {
+      log("Unable to find next sigprocmask in signal chain");
+      abort();
+    }
   }
 
   typedef int (*SigProcMask)(int how, const sigset_t*, sigset_t*);