[Crash-utility] add support for incomplete elf dump file

["Zhou, Wenjian/周文剑"]

Hello Dave,

On 10/22/2014 09:49 PM, Dave Anderson wrote:
>
> Hello Wenjian,
>
> First -- please send patches as email attachments.  Even if I cut-and-paste your
> patch from the crash-utility archives (which normally works), there are
> still no tabs in your patch.

Appreciate your suggestion.

> Now, with respect to the patch, it's not clear to me what would happen if you
> make no changes to check_dumpfile_size()?
>
> It seems to me that a read error would occur regardless whether you change
> the PT_LOAD-related contents or not.
>
> If no changes are made:
>
>    If a readmem() of a truncated page is attempted, read_netdump() would
>    calculate an offset based upon the original PT_LOAD contents, but then
>    the subsequent read() would fail, and would return a READ_ERROR.
>
> If your patch is applied:
>
>    If a readmem() of a truncated page is attempted, read_netdump() would not
>    be able to calculate an offset, and would return a READ_ERROR.
>
> What's the difference?  Why even bother making the changes?
>
If my patch is applied:
	If a readmem() of a truncated page is attempted,

	(pls->zero_fill && (paddr >= pls->phys_end) && (paddr < pls->zero_fill))
	
	,this will be right. So read_netdump() will fill bufptr with zero and
	return cnt.

In my patch, information of PT_LOAD segment is modified, so that the segment will
not go beyond the file size. And use zero to replace the lost part.

Previously, we intend to do this work in makedumpfile by modifying the PT_LOAD
header of the ELF dump file. But kumagai atsushi thought it's not good to make the
irreversible change. So we think do it in crash maybe a better choice.

> I also don't understand what the difference between "truncated" and "incomplete"
> is?  Why did you separate the messages into two?
>
At first, I thought the difference is the incomplete flag.
Now, I think it's not necessary to distinguish them.


> Anyway, I had already created a patch in preparation for the changes to
> makedumpfile for ELF and compressed kdump vmcores.  The patch will apply
> to the current github master branch.  Please apply it alone, and tell me
> what happens.

The patch can show the incomplete information, but will be interrupted by the
READ_ERROR (we don't change the PT_LOAD headers in makedumpfile any more).


Thanks
Zhou Wenjian

-------------- next part --------------
An embedded and charset-unspecified text was scrubbed...
Name: SUPPORT_INCOMPLETE_ELF.patch
URL: <http://listman.redhat.com/archives/crash-utility/attachments/20141023/3f903ce5/attachment.ksh>