Debug SIGTERM handler in Xcode?

Xcode 6.3.2


I have a daemon that hooks SIGHUP, SIGINT, and SIGTERM. They all direct the signals to call a signal_handler() function.


I was having an intermittent crash when the daemon was existing, so I ran the process in Xcode hoping to catch the problem. Unfortunately, I can't reproduce it. When I send the process a SIGTERM (kill -TERM <pid>), Xcode breaks in my run loop and says my process received a SIGTERM. Unexpected, but OK.


But then I click on the Continue button and ... nothing happens. The program goes right back to running normally, The signal_handler() function is never called.


Does anyone know how I can debug signals using the debugger, without the debugger intercepting it and "eating" the signal?

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JamesB
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You need to use the "process signal SIGTERM" command at the lldb console prompt to continue and deliver the signal.


Alternatively, you can use "process handle -s0 -p1 SIGTERM" in advance to tell the debugger to not stop when the signal is received and to pass it along to the debugee.

Posted by
Ken Thomases
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You need to use the "process signal SIGTERM" command at the lldb console prompt to continue and deliver the signal.


Alternatively, you can use "process handle -s0 -p1 SIGTERM" in advance to tell the debugger to not stop when the signal is received and to pass it along to the debugee.

Posted by
Ken Thomases
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Ken,


Thanks a million! That did the trick nicely. For future reference, the lldb command to change how the debugger handles a specific signal is


process handle <SIGNALNAME> [ --pass <true|false|1|0> ] [ --stop <true|false|1|0> ] [ --notify <true|false|1|0> ]


--pass determines if the signal will be passed to the process' signal handler

--stop determines if the debugger will stop your process when a signal is received

--notify controls whether a message about the signal gets logged


In my case, the solution was: process handle SIGTERM --stop false --pass true

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JamesB
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Is it possible to configure Xcode, so the the lldb always does the "process handle SIGTERM --stop false --pass true"?

When launching the app inside Xcode?

instead of always having to type in the "process handle SIGTERM --stop false --pass true" everytime (it's getting a bit tedious to re-type this everytime you CMD+R the app, when you are testing that it's handling the signals correctly ....)

Would be nice if there was a setting in inside Xcode, that you could configure the lldb with what you want it to do each time.

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danalien
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You can put a breakpoint that executes the lldb command and automatically continues somewhere in your app startup code. See https://stackoverflow.com/a/25631359/292145

Posted by
klaas
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