Re: [PATCH] Add --core-pattern option to eu-stack

[Jan Kratochvil <jan.kratochvil@redhat.com>]

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On Thu, 27 Nov 2014 12:04:39 +0100, Mark Wielaard wrote:
> On Wed, 2014-11-26 at 15:32 +0100, Jan Kratochvil wrote:
> > Therefore they are dead at the core_pattern time, they cannot be ptraced and
> > therefore they cannot be unwound. One could only find them in the core file
> > itself but that is outside of the scope of this eu-stack feature.
> 
> Why do you think that is out of scope? We get both the actual tid
> through the command line option and the core file through stdin. Can't
> we combine those two to get all information we want/need?

It could be extended that way but:

Currently elfutils is used only for the list of unwound PCs.  There is missing
a big part of functionality present in GDB - displaying parameters, local
variables, entry-value recovered values, data types pretty printing etc.
And I have doubts unwind of non-crashed threads is useful at all.

It is a new functionality on top of this patch that it has to read thread
registers from PT_NOTE but access the memory via ptraced crashed thread.
Fortunately core file PT_NOTE is first so it can be read quickly:
Program Headers:
  Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
  NOTE           0x0004a0 0x0000000000000000 0x0000000000000000 0x0005f4 0x000000     0
As reading the whole core file is in many times not possible (without some
better kernel core dumping interface):
	-fsanitize=address locks up abrt-hook-ccpp
	https://bugzilla.redhat.com/show_bug.cgi?id=1164548

So I agree your proposal makes some sense but:
 * I find it an incremental feature on top of this one.
 * Given elfutils just lists the unwound PCs I do not see how it is useful.

What is your - or Martin's - opinion on such feature given these contraints?


Thanks,
Jan