1 files changed, 51 insertions, 0 deletions
diff --git a/js/src/gdb/mozilla/asmjs.py b/js/src/gdb/mozilla/asmjs.py
new file mode 100644
index 0000000000..85a19a5cfc
--- /dev/null
+++ b/js/src/gdb/mozilla/asmjs.py
@@ -0,0 +1,51 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""
+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 WasmFaultHandler is installed as the SIGSEGV signal action.
+        sigaction_fn = gdb.parse_and_eval(
+            "(void(*)(int,void*,void*))__sigaction"
+        ).dereference()
+        sigaction_fn(SIGSEGV, 0, buf)
+        WasmTrapHandler = gdb.parse_and_eval("WasmTrapHandler")
+        if buf["__sigaction_handler"]["sa_handler"] == WasmTrapHandler:
+            # Advise the user that magic is happening.
+            print("js/src/gdb/mozilla/asmjs.py: Allowing WasmTrapHandler to run.")
+
+            # If WasmTrapHandler 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)