AX_CHECK_X86_FEATURES behaviour

Kip Warner <[email protected]> Mon, 27 May 2019 11:28:12 -0700

Newsgroups	gmane.comp.sysutils.autoconf.archive-maintainers
Message-ID	<[email protected]>

Hey list,

I am using AX_CHECK_X86_FEATURES in my configure.ac to check for
various CPU features. 

I noticed when building for s390x architecture the macro bailed because
the s390x' gcc's __builtin_cpu_init function is needed to perform the
probe but doesn't exist. I read up on that function and it appears
that's only available on i*86 and amd64 hosts. 

What I had expected the macro to do was to check for certain features,
set various flags accordingly, and that's it. If the
__builtin_cpu_init() function doesn't exist, I would have expected it
to set all flags to false and that would be the end of it.

I realize it may be tempting to suggest that one should only use this
macro when they are certain the host (or build as well?) are of i*86 or
amd64 architectures, but that partially defeats the whole point of the
macro and the intention behind portable configure scripts.

Should this be considered a design flaw or bug in
AX_CHECK_X86_FEATURES? Or should I check prior to calling it whether it
can be called?

-- 
Kip Warner | Senior Software Engineer
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https://www.thevertigo.com

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