linux-kernel - Re: Build/boot problem with 7b4537199a4a (Re: [PATCH v6 02/10] kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL

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Message-ID: <0da799d5-aa19-b116-89ce-0ca37780624a@csgroup.eu>
Date:   Sat, 20 Aug 2022 17:51:38 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Masahiro Yamada <masahiroy@...nel.org>
CC:     "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Peter Zijlstra <peterz@...radead.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>,
        Ard Biesheuvel <ardb@...nel.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: Build/boot problem with 7b4537199a4a (Re: [PATCH v6 02/10]
 kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS)



Le 20/08/2022 à 19:01, Masahiro Yamada a écrit :
> On Sat, Aug 20, 2022 at 11:15 PM Christophe Leroy
> <christophe.leroy@...roup.eu> wrote:
>>
>>
>>
>> Le 20/08/2022 à 14:51, Masahiro Yamada a écrit :
>>> On Sat, Aug 20, 2022 at 7:02 PM Christophe Leroy
>>> <christophe.leroy@...roup.eu> wrote:
>>>>
>>>> Hi,
>>>>
>>>> Le 13/05/2022 à 13:39, Masahiro Yamada a écrit :
>>>>> include/{linux,asm-generic}/export.h defines a weak symbol, __crc_*
>>>>> as a placeholder.
>>>>>
>>>>> Genksyms writes the version CRCs into the linker script, which will be
>>>>> used for filling the __crc_* symbols. The linker script format depends
>>>>> on CONFIG_MODULE_REL_CRCS. If it is enabled, __crc_* holds the offset
>>>>> to the reference of CRC.
>>>>>
>>>>> It is time to get rid of this complexity.
>>>>>
>>>>> Now that modpost parses text files (.*.cmd) to collect all the CRCs,
>>>>> it can generate C code that will be linked to the vmlinux or modules.
>>>>>
>>>>> Generate a new C file, .vmlinux.export.c, which contains the CRCs of
>>>>> symbols exported by vmlinux. It is compiled and linked to vmlinux in
>>>>> scripts/link-vmlinux.sh.
>>>>>
>>>>> Put the CRCs of symbols exported by modules into the existing *.mod.c
>>>>> files. No additional build step is needed for modules. As before,
>>>>> *.mod.c are compiled and linked to *.ko in scripts/Makefile.modfinal.
>>>>>
>>>>> No linker magic is used here. The new C implementation works in the
>>>>> same way, whether CONFIG_RELOCATABLE is enabled or not.
>>>>> CONFIG_MODULE_REL_CRCS is no longer needed.
>>>>>
>>>>> Previously, Kbuild invoked additional $(LD) to update the CRCs in
>>>>> objects, but this step is unneeded too.
>>>>>
>>>>> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
>>>>> Tested-by: Nathan Chancellor <nathan@...nel.org>
>>>>> Tested-by: Nicolas Schier <nicolas@...sle.eu>
>>>>> Reviewed-by: Nicolas Schier <nicolas@...sle.eu>
>>>>
>>>> Problem with v6.0-rc1
>>>> Problem with v5.19
>>>> No problem with v5.18
>>>>
>>>> Bisected to 7b4537199a4a ("kbuild: link symbol CRCs at final link,
>>>> removing CONFIG_MODULE_REL_CRCS")
>>>>
>>>> The above patch leads to the following problem building
>>>> mpc85xx_defconfig + CONFIG_RELOCATABLE
>>>
>>>
>>>
>>> Is this because the relocation implementation on ppc is incomplete?
>>> (and is it the reason why relock_check.sh exists?)
>>>
>>> arch/powerpc/kernel/reloc_32.S does not support R_PPC_UADDR32
>>>
>>>
>>
>> Might be the reason.
>>
>> Is it expected that your patch adds an unsupported relocation ?
>>
>> Why was that relocation type unneeded before ?
>>
>> Thanks
>> Christophe
> 
> 
> I posted a patch (although I believe my commit is innocent).
> 
> https://lore.kernel.org/lkml/20220820165129.1147589-1-masahiroy@kernel.org/T/#u
> 
> The relocs_check.sh warnings are gone.
> Please do a boot test.
> Thanks.
> 

Yes it works, many Thanks.

The fixes tag should probably be c857c43b34ec ("powerpc: Don't use a 
function descriptor for system call table")


Christophe