linux-kernel - Re: [PATCH] scripts/gdb: Handle split debug

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Message-ID: <9e3604b2-57dd-7f79-392d-47bb34eb5137@siemens.com>
Date:   Wed, 31 Jul 2019 18:23:53 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Kieran Bingham <kbingham@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        kgdb-bugreport@...ts.sourceforge.net,
        Jason Wessel <jason.wessel@...driver.com>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Stephen Boyd <swboyd@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] scripts/gdb: Handle split debug

On 31.07.19 17:44, Doug Anderson wrote:
> Hi,
> 
> On Wed, Jul 31, 2019 at 7:24 AM Jan Kiszka <jan.kiszka@...mens.com> wrote:
>>
>> On 31.07.19 01:40, Douglas Anderson wrote:
>>> Some systems (like Chrome OS) may use "split debug" for kernel
>>> modules.  That means that the debug symbols are in a different file
>>> than the main elf file.  Let's handle that by also searching for debug
>>> symbols that end in ".ko.debug".
>>
>> Is this split-up depending on additional kernel patches, is this already
>> possible with mainline, or is this purely a packaging topic? Wondering because
>> of testability in case it's downstream-only.
> 
> It is a packaging topic.  You can take a normal elf file and split the
> debug out of it using objcopy.  Try "man objcopy" and then take a look
> at the "--only-keep-debug" option.  It'll give you a whole recipe for
> doing splitdebug.  The suffix used for the debug symbols is arbitrary.
> If people have other another suffix besides ".ko.debug" then we could
> presumably support that too...
> 
> For portage (which is the packaging system used by Chrome OS) split
> debug is supported by default (and the suffix is .ko.debug).  ...and
> so in Chrome OS we always get the installed elf files stripped and
> then the symbols stashed away.
> 
> At the moment we don't actually use the normal portage magic to do
> this for the kernel though since it affects our ability to get good
> stack dumps in the kernel.  We instead pass a script as "strip" [1].
> 
> 
> [1] https://chromium.googlesource.com/chromiumos/overlays/chromiumos-overlay/+/refs/heads/master/eclass/cros-kernel/strip_splitdebug
> 
> 
> -Doug
> 

Thanks, makes perfect sense to me. You may add my

Reviewed-by: Jan Kiszka <jan.kiszka@...mens.com>

Jan

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