linux-kernel - Re: [PATCH] scripts/gdb: fix debugging modules compiled with hot/cold partitioning

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Message-Id: <565ED332-3D0E-4741-BB82-3E82371C7054@linux.ibm.com>
Date:   Thu, 31 Oct 2019 10:56:42 +0100
From:   Ilya Leoshkevich <iii@...ux.ibm.com>
To:     Jan Kiszka <jan.kiszka@...mens.com>
Cc:     Kieran Bingham <kbingham@...nel.org>, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH] scripts/gdb: fix debugging modules compiled with hot/cold
 partitioning

> Am 30.10.2019 um 19:29 schrieb Jan Kiszka <jan.kiszka@...mens.com>:
> 
> On 28.10.19 16:27, Ilya Leoshkevich wrote:
>> gcc's -freorder-blocks-and-partition option makes it group frequently
>> and infrequently used code in .text.hot and .text.unlikely sections
>> respectively. At least when building modules on s390, this option is
>> used by default.
>> 
>> gdb assumes that all code is located in .text section, and that .text
>> section is located at module load address. With such modules this is no
>> longer the case: there is code in .text.hot and .text.unlikely, and
>> either of them might precede .text.
>> 
>> Fix by explicitly telling gdb the addresses of code sections.
>> 
>> It might be tempting to do this for all sections, not only the ones in
>> the white list. Unfortunately, gdb appears to have an issue, when telling
>> it about e.g. loadable .note.gnu.build-id section causes it to think that
>> non-loadable .note.Linux section is loaded at address 0, which in turn
>> causes NULL pointers to be resolved to bogus symbols. So keep using the
>> white list approach for the time being.
> 
> Did you report this to gdb?

Yes: https://sourceware.org/bugzilla/show_bug.cgi?id=25152

Best regards,
Ilya