linux-kernel - Re: arm crypto .S_shipped files sometimes get rebuilt randomly

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Date:   Thu, 8 Mar 2018 14:00:03 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     Leonard Crestez <leonard.crestez@....com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: arm crypto .S_shipped files sometimes get rebuilt randomly

2018-03-08 4:25 GMT+09:00 Leonard Crestez <leonard.crestez@....com>:
> Hello,
>
> I am using a toolchain with a broken/old version of perl which doesn't
> include integer.pm and I noticed it triggers occasional build failures
> on arch/arm64/crypto/sha512-core.S_shipped. Workarounds are easy, but
> if the purpose of the .S_shipped is to avoid the need to have all
> dependencies on the build machine then something went wrong?
>
> This was introduced by commit 7918ecef073f ("crypto: arm64/sha2 -
> integrate OpenSSL implementations of SHA256/SHA512"). The makefile
> rules are not terribly complicated:
>
> quiet_cmd_perlasm = PERLASM $@
>       cmd_perlasm = $(PERL) $(<) void $(@)
>
> $(src)/sha512-core.S_shipped: $(src)/sha512-armv8.pl
>         $(call cmd,perlasm)
>
> If a decision to rerun the rule is made based on their relative
> timestamps but both .S_shipped and sha512-armv8.pl are included in git
> then won't the result be essentially random, depending on file checkout
> order?
>
> I see random success/failure by just running something like the
> following multiple times:
>         rm -rf arch/arm64/crypto
>         git co -f arch/arm64/crypto
>         make -- arch/arm64/crypto/
>
> A reasonable fix might be to simply drop .S_shipped and require a
> functional recent version of perl. Then if it fails it will fail
> reliably.
>

Indeed, this Makefile is weird.
We have two choices.


[1] If we intend to generate
sha{256,512}-core.S from the perl script during the build,
this should be:

$(obj)/sha512-core.S: $(src)/sha512-armv8.pl
        $(call cmd,perlasm)

$(obj)/sha512-core.S: $(src)/sha512-armv8.pl
        $(call cmd,perlasm)


[2] If we want to check-in _shipped files
and avoid running perl during the build,
we can surround unnecessary rules with if-conditional, like


if REGENERATE_ARM64_SHA
$(src)/sha256-core.S_shipped: $(src)/sha512-armv8.pl
        $(call cmd,perlasm)

$(src)/sha512-core.S_shipped: $(src)/sha512-armv8.pl
        $(call cmd,perlasm)
endif


Set REGENERATE_ARM64_SHA=1 from the command line
only when you need to update the _shipped files.

This is what commit 7373f4f83c71d50f0aece6d94309ab7fde42180f did.




Recently, Kconfig switched to [1].
So, flex and bison are required to build the kernel.

-- 
Best Regards
Masahiro Yamada