Bug#719355: building atlas armel on an armv7 system results in an armv7 build.

[peter green]

Package: atlas
Version: 3.10.1-2
Severity: important

While trying (and failing...) to patch the new version of the atlas 
packaging for raspbian I noticed an issue with the armel packaging.

In debian/rules for atlas is the following line

# - 0 means Unknown CPU: leave ATLAS find out; used for archs where a 
more specific choice is not available

This value of 0 is used on armel. This causes atlas to try and probe the 
system it's on and to decide what CPU to use. If the probe fails it then 
appears to go on and do a "generic" build.

When building the atlas package for armel on armv5 hardware (like debian 
currently uses for it's autobuilders) this is not a problem, atlas can't 
detect a CPU to use and falls back to doing a generic build. However if 
one tries to build the armel package on an armv7 machine then atlas will 
detect and build for armv7.

I looked to see if there was an option to force atlas to do a generic 
build though command line options but I couldn't find one, only ways to 
force particular CPUs. For raspbian I patched the upstream build system 
to hack out the autodetection and hence force a generic build but I'm 
not sure if you want to go down that route for debian or if there is a 
better soloution. I've thrown a copy of this patch into this mail in 
case it's helpful but it may be related to the failures i've been having 
with raspbian so I certainly wouldn't apply it without testing.

It is not acceptable for building an armel package on an armv7 system to 
result in a package that requires armv7. Debian package building must 
produce a package that will run on the minimum hardware for the debian 
architecture in question even if the machine used to do the build is 
significantly above the minimum hardware for the architecture. It is 
very likely that at some point in the future debian will switch to using 
armv7 hardware for armel autobuilders.

I've attached a partial build log demonstrating atlas for armel deciding 
to configure itself for armv7 (I cancelled the build once i'd seen 
enough to convince me that the build was suffering from the problem)

P.S. If you need access to an armv7 machine with an armel chroot there 
is ipa.debian.net though it's down right now 
http://lists.debian.org/debian-arm/2013/05/msg00099.html 
http://lists.debian.org/debian-arm/2013/08/msg00007.html

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