linux-kernel - Re: mmap'ed memory in core files ?

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Message-ID: <cfd18e0f0807012214o78353faal84a5fa764d3210bf@mail.gmail.com>
Date:	Wed, 2 Jul 2008 07:14:22 +0200
From:	"Michael Kerrisk" <mtk.manpages@...glemail.com>
To:	"Bron Gondwana" <brong@...tmail.fm>
Cc:	"Michael Kerrisk" <mtk.manpages@...il.com>,
	"Philippe De Muyter" <phdm@...qel.be>,
	linux-kernel@...r.kernel.org, robm@...tmail.fm
Subject: Re: mmap'ed memory in core files ?

On Tue, Jul 1, 2008 at 11:44 PM, Bron Gondwana <brong@...tmail.fm> wrote:
> On Tue, Jul 01, 2008 at 08:16:11PM +0200, Michael Kerrisk wrote:
>> On 7/1/08, Philippe De Muyter <phdm@...qel.be> wrote:
>> > Hello everybody,
>> >
>> >  I develop video acquisition software using the video1394 interface.
>> >  The images grabbed by the camera and iee1394 bus are kept in kernel
>> >  memory and made available to the user program through a mmap call done
>> >  in the libdc1394 library :
>> >
>> >  dma_ring_buffer= mmap(0, vmmap.nb_buffers * vmmap.buf_size,
>> >                 PROT_READ|PROT_WRITE,MAP_SHARED, craw->capture.dma_fd, 0);
>> >
>> >  Sometimes, my program crashes and produces a core file :)  It seems to
>> >  me that the core file does not contain the mmap'ed memory and hence
>> >  I cannot replay my program with the same image for debugging purpose.
>> >
>> >  Is it possible to configure the kernel through /proc, or through the mmap
>> >  system call to have that mmapped segment in the core file, or do I need
>> >  to modify the kernel itself to obtain the behaviour I want ?  If I
>> >  need to modify the kernel, can some kind soul provide me some pointers ?
>>
>>
>> Have a look at the section "Controlling which mappings are written to
>> the core dump" in a recent core.5 man page:
>> http://www.kernel.org/doc/man-pages/online/pages/man5/core.5.html
>
> Interesting (and somewhat off topic to your conversation here) - it
> appears that when dumping mappings, the kernel ignores the maximum
> core size set with "limit".
>
> This is particularly interesting on a 64 bit kernel where a bug in
> your code causes you to try to read something about 2Gb into your
> alleged mmaped file (actual size ~500 bytes) and the segfault causes
> a coredump.

Do you have a ssimple example program for this?

-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
man-pages online: http://www.kernel.org/doc/man-pages/online_pages.html
Found a bug? http://www.kernel.org/doc/man-pages/reporting_bugs.html
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