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

[Michael Ellerman <mpe@ellerman.id.au>]

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
> 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