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"""
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)
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