1 files changed, 40 insertions, 0 deletions
diff --git a/js/src/gdb/mozilla/asmjs.py b/js/src/gdb/mozilla/asmjs.py
new file mode 100644
index 000000000..43fac20c7
--- /dev/null
+++ b/js/src/gdb/mozilla/asmjs.py
@@ -0,0 +1,40 @@
+"""
+In asm code, out-of-bounds heap accesses cause segfaults, which the engine
+handles internally. Make GDB ignore them.
+"""
+
+import gdb
+
+SIGSEGV = 11
+
+# A sigaction buffer for each inferior process.
+sigaction_buffers = {}
+
+def on_stop(event):
+    if isinstance(event, gdb.SignalEvent) and event.stop_signal == 'SIGSEGV':
+        # Allocate memory for sigaction, once per js shell process.
+        process = gdb.selected_inferior()
+        buf = sigaction_buffers.get(process)
+        if buf is None:
+            buf = gdb.parse_and_eval("(struct sigaction *) malloc(sizeof(struct sigaction))")
+            sigaction_buffers[process] = buf
+
+        # See if AsmJSFaultHandler is installed as the SIGSEGV signal action.
+        sigaction_fn = gdb.parse_and_eval('__sigaction')
+        sigaction_fn(SIGSEGV, 0, buf)
+        AsmJSFaultHandler = gdb.parse_and_eval("AsmJSFaultHandler")
+        if buf['__sigaction_handler']['sa_handler'] == AsmJSFaultHandler:
+            # Advise the user that magic is happening.
+            print("js/src/gdb/mozilla/asmjs.py: Allowing AsmJSFaultHandler to run.")
+
+            # If AsmJSFaultHandler doesn't handle this segfault, it will unhook
+            # itself and re-raise.
+            gdb.execute("continue")
+
+def on_exited(event):
+    if event.inferior in sigaction_buffers:
+        del sigaction_buffers[event.inferior]
+
+def install():
+    gdb.events.stop.connect(on_stop)
+    gdb.events.exited.connect(on_exited)