Re: [PATCH] powerpc: align syscall table for ppc32

From: Masahiro Yamada <masahiroy@kernel.org>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] powerpc: align syscall table for ppc32
Date: Thu, 25 Aug 2022 22:13:56 +0900	[thread overview]
Message-ID: <CAK7LNAQ8ZQHYzoJTPxiRYBsdVXdYUt=bxyrag-d7UnwQ9r7q=w@mail.gmail.com> (raw)
In-Reply-To: <874jy0lpy9.fsf@mpe.ellerman.id.au>

On Thu, Aug 25, 2022 at 4:53 PM Michael Ellerman <mpe@ellerman.id.au> wrote:
>
> Masahiro Yamada <masahiroy@kernel.org> writes:
> > Christophe Leroy reported that commit 7b4537199a4a ("kbuild: link
> > symbol CRCs at final link,  removing CONFIG_MODULE_REL_CRCS") broke
> > mpc85xx_defconfig + CONFIG_RELOCATABLE=y.
> >
> >     LD      vmlinux
> >     SYSMAP  System.map
> >     SORTTAB vmlinux
> >     CHKREL  vmlinux
> >   WARNING: 451 bad relocations
> >   c0b312a9 R_PPC_UADDR32     .head.text-0x3ff9ed54
> >   c0b312ad R_PPC_UADDR32     .head.text-0x3ffac224
> >   c0b312b1 R_PPC_UADDR32     .head.text-0x3ffb09f4
> >   c0b312b5 R_PPC_UADDR32     .head.text-0x3fe184dc
> >   c0b312b9 R_PPC_UADDR32     .head.text-0x3fe183a8
> >       ...
> >
> > The compiler emits a bunch of R_PPC_UADDR32, which is not supported by
> > arch/powerpc/kernel/reloc_32.S.
> >
> > The reason is there exists an unaligned symbol.
> >
> >   $ powerpc-linux-gnu-nm -n vmlinux
> >     ...
> >   c0b31258 d spe_aligninfo
> >   c0b31298 d __func__.0
> >   c0b312a9 D sys_call_table
> >   c0b319b8 d __func__.0
> >
> > Commit 7b4537199a4a is not the root cause. Even before that, I can
> > reproduce the same issue for mpc85xx_defconfig + CONFIG_RELOCATABLE=y
> > + CONFIG_MODVERSIONS=n.
> >
> > It is just that nobody did not notice it because when CONFIG_MODVERSIONS

I wrote weird English (double negation)

nobody did not notice   --> nobody noticed

Please fix it if you have not yet.

Thank you.

> > is enabled, a __crc_* symbol inserted before sys_call_table was hiding
> > the unalignment issue.
> >
> > I checked the commit history, but I could not understand commit
> > 46b45b10f142 ("[POWERPC] Align the sys_call_table").
> >
> > It said 'Our _GLOBAL macro does a ".align 2" so the alignment is fine
> > for 32 bit'. I checked the _GLOBAL in include/asm-powerpc/ppc_asm.h
> > at that time. _GLOBAL specifies ".align 2" for ppc64, but no .align
> > for ppc32.
> >
> > Commit c857c43b34ec ("powerpc: Don't use a function descriptor for
> > system call table") removed _GLOBAL from the syscall table.
> >
> > Anyway, adding alignment to the syscall table for ppc32 fixes the issue.
> >
> > I am not giving Fixes tag because I do not know since when it has been
> > broken, but presumably it has been for a long while.
>
> Thanks.
>
> I trimmed the change log a bit just to say ~= it's been broken for ever,
> and added a Cc to stable.
>
> cheers

-- 
Best Regards
Masahiro Yamada