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Date: Mon, 24 Nov 2008 18:34:56 +0100 From: "Frédéric Weisbecker" <fweisbec@...il.com> To: "Steven Rostedt" <rostedt@...dmis.org> Cc: "Ingo Molnar" <mingo@...e.hu>, "Linux Kernel" <linux-kernel@...r.kernel.org> Subject: Re: Human readable output for function return tracer 2008/11/24 Steven Rostedt <rostedt@...dmis.org>: > A little off topic, but how do you handle collapsed returns? > > func1() { > [...] > func2(); > return; > } > > Instead of using call *func2, gcc may decide to collapse it. That is, > since it is the last thing done on func1, it may pop func1's frame all the > way to func1's return address, and then do a "jmp" to func2. func2 will > still call mcount, but on its return, it will jump to the func1 return > address. > > Perhaps this is OK. The call to func1's mcount will store the original > return address and replace it with the function return code. The call to > func2 will store that return address and replace it with the func2 > function return code. And both of them will still be processed. > > OK, I think I answered my own question, but I'm keeping it in this post > just to make sure I understand it correctly. Yes, perhaps it is done that way. Or perhaps CONFIG_FRAME_POINTER avoids such collapsing calls... I don't know. Perhaps I should look at some disassembly dumps to ensure things are safe, but I didn't have any problem with that... > Do you have a record that you store when you make the first mcount call. > In this record, could you save the depth of the parent there too. I do not > remember the code exactly, so I might be off here ;-) No. At this time I don't do any insertion at the call time :-) But I don't think I will need the parent depth. The current depth will be sufficient for the trace printing. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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