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Re: arm specific patches

On Sun, 2008-03-23 at 11:14 +0000, David Goodenough wrote:
> In the patches for util-linux, apt, dpkg, gnupg and mktemp there are patches 
> build a file called arm-linux-gnu.cache.  This file is then copied into the
> build tree.

It is put in place by emsource when the patches are applied but it is
ignored by any non-arm-linux-gnu build - each arch would need their own
and emsource/emdebuild support this.

Native builds ignore it completely so your i386 builds do not need any
cache files, ./configure can run AC_TRY directly because you aren't
using a cross compiler.

> Now I realise that the patches can not build an architecture specific file,
> we can not substitute into the diff file names.  

One file per arch, one patch per arch. (Until we come up with a better

> So would it not be better to create a file called generic.cache,

Already exists - dpkg-cross already has a generic cache file for each
arch for values that many applications need. Some of the current cache
values may migrate into there but most are entirely specific to that one

>  and then
> when the cp is done to copy it into the build tree to convert it into an
> architecture specific file name:-
> cp generic.cache build-deb/$DEB_HOST_GNU_TYPE.cache

No. The values themselves differ between architectures, that's why we
have .cache files in the first place. The value of having
arm-linux-gnu.cache is that when preparing a build for armel or mipsel,
you have a head start on *which* cache values may be needed. It is then
simply a case of looking up those values in the native Debian build log
and setting them in the new cache file.

The problem with cache files is that the cache values might actually
change and then we'd be building the wrong setup. A better solution is
needed but a generic cache file is not it. We need improved support in
autotools so that AC_TRY automatically has a replacement when cross
building instead of just dieing which is actually very rude. Overall, I
would like to see cross-building cleanly supported in autotools with
some degree of backwards-compatibility, so that an update in autoconf
would allow many applications to build a ./configure script that does
not simply die when cross building is detected but I suspect it needs
changes to hundreds of m4 files across the internet. :-(

> Also, how does the emsource program know which patches are architecture
> specific, so that it can ignore patches which are not relevant to the
> architecture you are building?

It doesn't need to - the patch to debian/rules already handles that via

i.e. ./configure is passed the architecture-specific cache file but only
if the DEB_HOST_GNU_TYPE differs from DEB_BUILD_GNU_TYPE. In your case,
even that is ignored.


Neil Williams

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