Re: mmap'ed memory in core files ?

Michael Kerrisk
2008-07-02T05:14:34Z

On Tue, Jul 1, 2008 at 11:44 PM, Bron Gondwana <brong@fastmail.fm> wrote:
> On Tue, Jul 01, 2008 at 08:16:11PM +0200, Michael Kerrisk wrote:
>> On 7/1/08, Philippe De Muyter <phdm@macqel.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
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