linux-kernel - Re: [PATCH] scripts/gdb: fix debugging modules on s390

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Date:   Thu, 17 Oct 2019 09:05:28 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>
Cc:     Kieran Bingham <kbingham@...nel.org>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH] scripts/gdb: fix debugging modules on s390

On 15.10.19 17:43, Ilya Leoshkevich wrote:
>> Am 15.10.2019 um 17:21 schrieb Jan Kiszka <jan.kiszka@...mens.com>:
>>
>>> @@ -113,6 +113,12 @@ lx-symbols command."""
>>>         if module_file:
>>>             gdb.write("loading @{addr}: {filename}\n".format(
>>>                 addr=module_addr, filename=module_file))
>>> +            if utils.is_target_arch('s390'):
>>> +                # Module text is preceded by PLT stubs on s390.
>>> +                module_arch = module['arch']
>>> +                plt_offset = int(module_arch['plt_offset'])
>>> +                plt_size = int(module_arch['plt_size'])
>>> +                module_addr = hex(int(module_addr, 0) + plt_offset + plt_size)
>>
>> Shouldn't we report the actual address above, ie. reorder this tuning
>> with the gdb.write?
> 
> That's a tough question. I thought about this, and the argument for
> showing the fixed up address is that if someone does the math with
> symbol offsets from e.g. objdump, the result will be consistent with
> what gdb shows.
> 
> On the other hand side, why would anyone do this? that's exactly what
> this gdb script is for. So showing the actual address at which the
> memory was allocated gives the user some additional information, and is
> also consistent with what cat /proc/modules would show.
> 
> At the end of the day, I don't have a strong opinion on this, so if you
> think it's better to show the fixed up address, I'll send a v2.

One of the original ideas of the printout was to provide the information
needed to reproduce potential issues manually. From that perspective,
the fixed-up address would the the thing to print.

If you think the vanilla address has some value as well, we could make
an s390-specifi printout of both values.

Jan

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