linux-kernel - Re: Extending coredump note section to contain filenames

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Message-ID: <20120309172934.GA18173@host2.jankratochvil.net>
Date:	Fri, 9 Mar 2012 18:29:34 +0100
From:	Jan Kratochvil <jan.kratochvil@...hat.com>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Roland McGrath <mcgrathr@...gle.com>, linux-kernel@...r.kernel.org,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: Extending coredump note section to contain filenames

Hi Denys,

On Fri, 09 Mar 2012 18:13:49 +0100, Denys Vlasenko wrote:
> gdb retrieves loaded library names by examining dynamic loader's
> data stored in the coredump's data segments. It uses intimate
> knowledge how and where dynamic loader keeps the list of loaded
> libraries.

this is the backward compatible way and it is no longer the right one with
build-ids.

GDB should scan the address space for mapped build-ids and map symbol files
accordingly.  The shared library list may be even corrupted in crashes with
memory overruns.  But it has not been implemented yet, I plan it for years.

(It can use the shared library list as a hint as in some cases the symbol
files could overlap if you load the first page of an ELF file etc., this is
very improbable possibility.)


> Another question is detection of deleted files.
> If /usr/lib/xulrunner-2/libmozjs.so was updated while program ran
> and now file mapped into process address space does not correspond
> to the same-named file on disk, can we help users to detect this? How?
> By saving maj/min/inode? Hash thereof?
> File size?
> File's md5sum (probably not, way too expensive. But nicely robust...)?

build-id is already being saved.  This is all that matters.  Filename does not
say anything - as you noticed it can be even already deleted, it can have
unknown content etc.  I do not see what problems you target here.


Regards,
Jan
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