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

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Date:   Wed, 7 Mar 2018 21:25:29 +0200
From:   Leonard Crestez <leonard.crestez@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: arm crypto .S_shipped files sometimes get rebuilt randomly

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.

--
Regards,
Leonard