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Re: [PATCH] stack: Add new '-n MAXFRAMES' option. Resolve addresses after unwind.
- From: Jan Kratochvil <jan dot kratochvil at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Thu, 02 Jan 2014 20:45:47 +0100
- Subject: Re: [PATCH] stack: Add new '-n MAXFRAMES' option. Resolve addresses after unwind.
On Mon, 23 Dec 2013 11:21:19 +0100, Mark Wielaard wrote:
> Limit the number of frames printed per thread (defaults to 64)
The new option is sure OK but any non-infinite default is not right:
* Normal applications have deeper stack than 64. When I broke into my
GTK running app it has 103 frames: http://people.redhat.com/jkratoch/app.bt
* Applications with deeper stack just take longer to unwind, that's normal.
If there is a special use case where target application should not be
stopped for a noticeable time then the '-n' option is perfect.
But this is not the default case.
* Such limit makes IMO sense only for runaway apps with "infinite" backtrace.
Such applications have probably already crashed (I am backtracing a core)
or the application is no longer responsive. In such case:
* It does not matter if eu-stack takes slightly longer or not.
* I really need the full unwind as only the top of stack can disclose
why the infinite deadlock occured.
Primarily I still miss a use case for this default of non-infinite limit.
* It does not warn that it stopped the unwind due to such a limit:
#62 0x000000000040054e bt
#63 0x000000000040054e bt
$ _ (rc = 0)
* One cannot easily make the unwind unlimited:
$ stack -p $p -n 0
stack: -n MAXFRAMES should be 1 or higher.
Try `stack --help' or `stack --usage' for more information.
$ ./src/stack -p $p -n -1
Program received signal SIGSEGV, Segmentation fault.
0x0000000000402974 in main (argc=5, argv=0x7fffffffd978) at stack.c:530
528 struct frames *frames = malloc (sizeof (struct frames)
529 + sizeof (struct frame) * maxframes);
530 -> frames->frames = 0;