Pigeon.
April 12th, 2013, 10:04 AM
Apologies for bumping an old thread but since it is currently the fourth result on google for dpkg-buildpackage "-ai386" and the reason I was googling that is to try and find out why it doesn't work, I figured it would be helpful to add to the thread having found a way to make it work.
Do not be discouraged by reading the package must be built on the correct arch in the above - it is not true, at least not for the case of building i386 packages on x86_64.
This bit...
To actually build a package for a different architecture you can pass the -a<arch> option to debuild (or dpkg-buildpackage). for example
$debuild -ai386 -b -us -uc
would build the binaries (unsigned) for i386 on an amd64 system, assuming you had all the necessary i386 libraries installed
...is wrong (at least, it is wrong for dpkg-buildpackage; I have not tried debuild). It appears to work, as in it creates .debs named blahblahblah_i386.deb, but all it has really achieved is to get dpkg-buildpackage to lie - the files inside those .debs are still built for x86_64.
The only indication that something may have gone wrong is the warning dpkg-architecture: warning: specified GNU system type i486-linux-gnu does not match gcc system type x86_64-linux-gnu, try setting a correct CC environment variable - which is right at the start of the output, and will most likely scroll off the top before you've even had a chance to notice it - and in any case the next line is dpkg-buildpackage: host architecture i386 which will make you think it's all OK anyway... when in fact it is not.
The solution I found was to set CC as follows:
export CC="gcc -m32 -Wl,-melf_i386"
before invoking dpkg-buildpackage. This translates as "invoke gcc with the flag -m32 to tell it to compile in 32-bit mode, and also pass -melf_i386 to ld to tell ld to link for i386". The output from dpkg-buildpackage still includes the same warnings, but this time it does build i386 .debs with i386 files inside.
Note that while this does work in my specific case (building a 32-bit version of libnl on x86_64) it may not work generally; it relies on the source package's build scripts and makefiles both honouring CC, and invoking ld via gcc instead of directly.
If ld is invoked directly the solution would probably be (untested):
export CC="gcc -m32"
export LD="ld -melf_i386"
If CC/LD are not honoured this may work:
export CFLAGS="-m32 -Wl,-melf_i386"
or
export CFLAGS="-m32"
export LDFLAGS="-melf_i386"
...but it may not; for example it may break the configure script and cause it to report that the compiler does not work. In that case probably the easiest solution (for suitable values of "easiest") would be to edit the scripts/makefiles so that they do honour CC/LD.
The official Debian recommendation is to create a chroot containing a complete 32-bit environment and build all your 32-bit packages inside that. This makes sense if you are building 32-bit packages all the time, but it is massive overkill to go to all that hassle just to build the odd one now and then.