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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Date:   Sat, 20 Aug 2022 14:15:18 +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 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