linux-kernel - Re: [PATCHv3 2/2] x86/vdso: Add build salt to the vDSO

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Message-ID: <CAK7LNARYXqx6U+fA2AuY00vMkMDbcNSf-VG_Avf+9j5AMLSsJw@mail.gmail.com>
Date:   Thu, 24 May 2018 10:43:55 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Mark Wielaard <mjw@...oraproject.org>,
        "H. J. Lu" <hjl.tools@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
        Nick Clifton <nickc@...hat.com>,
        Cary Coutant <ccoutant@...il.com>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>
Subject: Re: [PATCHv3 2/2] x86/vdso: Add build salt to the vDSO

2018-05-24 9:11 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> 2018-05-24 7:53 GMT+09:00 Laura Abbott <labbott@...hat.com>:
>> On 05/22/2018 05:33 PM, Andy Lutomirski wrote:
>>>
>>> On Tue, May 22, 2018 at 5:19 PM Laura Abbott <labbott@...hat.com> wrote:
>>>
>>>
>>>> The vDSO is linked separately from the kernel and modules. Ensure it
>>>> picks
>>>> up the comment section, if available.
>>>
>>>
>>> Did you end up preferring this to just sticking the kernel version in a
>>> .comment in the vDSO for some reason?
>>>
>>
>> Actually I remember now why this is necessary: there is not a simple way
>> to encode a string into a linker file as it has to be spit out byte
>> by byte. The autogeneration was the easiest way to make that happen.
>> Maybe there's some horrific c preprocessing or other generation that
>> could happen but I doubt that's any worse than the generated linker
>> script.
>>
>
>
> I am personally prefer CONFIG option (as you did in v2) to KERNELVERSION.
>
>
> If you use "hex" type instead of "string" type in Kconfig,
> and LONG() instead of BYTE() in the script script,
> this can be much simpler, right?
>
>
>
>
>
> config BUILD_ID_SALT
>         hex "Build ID Salt"
>         help
>            ...
>
>
>
>
> Then, in scripts/Makefile,
>
>
> define filechk_build-salt.lds
>         { \
>                 echo "SECTIONS {"; \
>                 echo ".comment (INFO) : { LONG($(CONFIG_BUILD_ID_SALT)); }"; \
>                 echo "}"; \
>         }
> endef
>
> $(obj)/build-salt.lds: $(src)/Makefile FORCE
>         $(call filechk,build-salt.lds)
>
>
>
>
> This is now so simple that we can even remove the shell script.



I had not noticed the comments from Linus and Andy
before I posted mine.


Maybe, we should not add binary data into the .comment section.



-- 
Best Regards
Masahiro Yamada