Catch SIGBUS in HeapWalker

SIGBUS shouldn't happen, since all of the regions being walked
were previously read out of /prod/pid/maps, but it seems to happen
rarely.  Catch it so it can produce a better log message.

Bug: 128983715
Test: atest memunreachable_test
Change-Id: I82d3941a382a0451c0dda12f5eb849ad8d697bc9
diff --git a/libmemunreachable/HeapWalker.h b/libmemunreachable/HeapWalker.h
index 9e3db08..f00bcca 100644
--- a/libmemunreachable/HeapWalker.h
+++ b/libmemunreachable/HeapWalker.h
@@ -52,7 +52,8 @@
         allocation_bytes_(0),
         roots_(allocator),
         root_vals_(allocator),
-        segv_handler_(),
+        sigsegv_handler_(allocator),
+        sigbus_handler_(allocator),
         walking_ptr_(0),
         walking_range_{0, 0},
         segv_logged_(false),
@@ -62,10 +63,14 @@
     valid_mappings_range_.end = 0;
     valid_mappings_range_.begin = ~valid_allocations_range_.end;
 
-    segv_handler_.install(
+    sigsegv_handler_.install(
         SIGSEGV, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {
           this->HandleSegFault(handler, signal, siginfo, uctx);
         });
+    sigbus_handler_.install(
+        SIGBUS, [=](ScopedSignalHandler& handler, int signal, siginfo_t* siginfo, void* uctx) {
+          this->HandleSegFault(handler, signal, siginfo, uctx);
+        });
   }
 
   ~HeapWalker() {}
@@ -106,7 +111,8 @@
   allocator::vector<Range> roots_;
   allocator::vector<uintptr_t> root_vals_;
 
-  ScopedSignalHandler segv_handler_;
+  ScopedSignalHandler sigsegv_handler_;
+  ScopedSignalHandler sigbus_handler_;
   volatile uintptr_t walking_ptr_;
   Range walking_range_;
   bool segv_logged_;