Bug#983807: spring builds with -march=native on amd64

From	Markus Koschany <apo@debian.org>
Newsgroups	linux.debian.bugs.rc
Subject	Bug#983807: spring builds with -march=native on amd64
Date	2021-03-02 00:20 +0100
Message-ID	<BNZZv-4oa-1@gated-at.bofh.it> (permalink)
References	<BNYK6-3tU-9@gated-at.bofh.it> <BNZwt-3Z2-1@gated-at.bofh.it> <BNZPP-4l8-1@gated-at.bofh.it> <BNYK6-3tU-9@gated-at.bofh.it> <BNZPP-4l8-1@gated-at.bofh.it>
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Control: severity -1 normal

Am Dienstag, den 02.03.2021, 01:02 +0200 schrieb Adrian Bunk:
> On Mon, Mar 01, 2021 at 11:39:00PM +0100, Markus Koschany wrote:
> > Am Montag, den 01.03.2021, 23:53 +0200 schrieb Adrian Bunk:
> > > Source: spring
> > > Version: 105.0.1+dfsg-1
> > > Severity: serious
> > > Tags: patch
> > > 
> > > spring builds with -march=native on amd64, which makes spring
> > > only work on machines compatible with whatever buildd built it.
> > 
> > What Policy violation justifies severity serious for this bug?
> 
> The release team agrees that baseline violations are severity serious.

What do you mean by baseline "violations"?

> Users can expect that all software we ship works on the baseline
> of an architecture.

Agreed. However I don't see that this assumption is not true for Spring
compiled with march=native on our buildd.

> 
> > Spring is only
> > built on i386/i686 and amd64. What difference does it make if we switch to
> > the
> > generic march=x86-64 when march=native appears to be working fine?
> > ...
> 
> It appears to work, and will work for you if your CPU is compatible with 
> whatever buildd happened to build it.
> 
> We used to have older AMD Opterons among the buildds,
> gcc would emit 3DNow! instructions that no modern CPU has.

I would really like to understand what the current drawback is for our users.
If you could provide the build flags with march=native and march=x86-64 and
then prove that march=x86-64 prevents some serious issues or makes the engine
better for users, I would happily apply your patch. Otherwise I am reluctant to
apply it because there is no current evidence that it improves the package. The
GCC manual talks about "it _might_" have some drawbacks but it also depends on
the package. Again where is the concrete drawback for Spring?

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Bug#983807: spring builds with -march=native on amd64 Markus Koschany <apo@debian.org> - 2021-03-02 00:20 +0100

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