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SubjectRe: [PATCH] [powerpc-next] Fix powerpc64 alignment of .toc section in kernel modules
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Hello Michael,

On 12/07/2017 10:25 AM, Michael Ellerman wrote:
> Hi Desnes,
>
> Am I right that Alan largely wrote this patch?
>
> If so it should probably be From: him, so that he is the author in the
> git log.

Yes, Alan Modra is the main author and I am just committing it with
minor changes. Thus, the author change is necessary.

>
>
> Desnes Augusto Nunes do Rosario <desnesn@linux.vnet.ibm.com> writes:
>> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
>> index 1381693..c472f5b 100644
>> --- a/arch/powerpc/Makefile
>> +++ b/arch/powerpc/Makefile
>> @@ -63,6 +63,7 @@ UTS_MACHINE := $(subst $(space),,$(machine-y))
>> ifdef CONFIG_PPC32
>> KBUILD_LDFLAGS_MODULE += arch/powerpc/lib/crtsavres.o
>> else
>> +KBUILD_LDFLAGS_MODULE += -T arch/powerpc/kernel/module.lds
>
> This needs to be:
>
> KBUILD_LDFLAGS_MODULE += -T $(srctree)/arch/powerpc/kernel/module.lds
>
> Otherwise building with O=../build fails with:
>
> ld: cannot open linker script file arch/powerpc/kernel/module.lds: No such file or directory
>
> I'll fix it up.

Indeed; this change is necessary to avoid any path errors.

>
>> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
>> index 759104b..9b2c5c1 100644
>> --- a/arch/powerpc/kernel/module_64.c
>> +++ b/arch/powerpc/kernel/module_64.c
>> @@ -374,11 +377,13 @@ int module_frob_arch_sections(Elf64_Ehdr *hdr,
>> }
>>
>> /* r2 is the TOC pointer: it actually points 0x8000 into the TOC (this
>> - gives the value maximum span in an instruction which uses a signed
>> - offset) */
>> + * gives the value maximum span in an instruction which uses a signed
>> + * offset). Round down to a 256 byte boundary for the odd case where
>> + * we are setting up r2 without a .toc section.
>> + */
>> static inline unsigned long my_r2(const Elf64_Shdr *sechdrs, struct module *me)
>> {
>> - return sechdrs[me->arch.toc_section].sh_addr + 0x8000;
>> + return (sechdrs[me->arch.toc_section].sh_addr & -256) + 0x8000;
>
> I think it's more typical in the kernel to write -256 as ~0xff.
>
> Again I can fix it up.

Good to know!

>
> cheers
>

Lastly, will you fix it up or do you want me to send a second version
then? Whatever is best for you.

Thank you for the review.

--
Desnes Augusto Nunes do Rosário
------------------------------------------

Linux Developer - IBM / Brazil
M.Sc. in Electrical and Computer Engineering - UFRN

(11) 9595-30-900
desnesn@br.ibm.com

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