additions to dpkg-architecture
Dear Debian Developers,
I've been pleased to summarize some ideas for the general public.
More details and sources can be found at the end of this mail.
I'm not subscribed to all lists, so please CC any replies to me.
I propose to add more CPU types to dpkg-architecture. In particular,
I'd like to see the different i386 architectures there, i.e.
i586, i686, k6, ...
The dpkg-cross tool is currently only used for cross compiling
applications. However, dpkg-cross is a more generic tool. The
"dpkg-buildpackage" wrapper of dpkg-cross allows you to compile
a package with different compilers, without the need to change
your debian/rules. (usually, some compatibility changes are needed
to make the debian/rules file "cleaner", but that's all)
For instance, some programs with lots of calculations (e.g. mplayer)
are compiled with different processor optimizations (e.g. mplayer-i586).
Such packages are created by very redundant entries in debian/rules.
Exactly such redundancy is removed by dpkg-cross.
Also, these optimized versions get names like "mplayer-i586",
but their architecture is set to "i386". That means, the *real*
architecture is encoded in the package name instead of the package's
This is a work around the inability of apt to automatically use
the best suited binary packages. (e.g. uses on a i686 system the
mplayer-i586 instead if mplayer-i386, and the kernel-image-i686)
If one day apt evolves, packages like mplayer-i586 will step in their
way. The "Package:" field should not contain architectural information.
The "Architecture:" field serves that purpose.
Until APT becomes aware of multiple architectures, this won't change
much. However, there are still lots of interesting cases where
more architectures are desirable.
For example, suppose you support a new OS, such as the w32 platform.
Currently, your only choice is "w32-i386", which means that you must
use an i486-mingw32msvc Compiler. However, for a w32 system a i486
compile doesn't make a lot of sense. Since those systems (except very
old Windows versions) need at least a Pentium, it is reasonable to
compile such a distribution at least for i586, not i486.
That means, the "linux" OS dictates that i386 should mean "at least
i486", while other OSes (e.g. win32) have different needs (e.g. "at
least i586"). Such dependencies between the OS and CPU type are simply
unnecessary and disturbing.
In that example, there should be a "linux-i386" platform (which may
be abbreviated to i386), while dpkg-architecture should also allow
a Debian platform like "w32-i586". This proposal is similar to
the addition of multiple arm CPU variants to dpkg-architecture.
Of course, if you want to allow, e.g. the -i386 packaes to be installed
on a -i586 distribution, some bigger parts of dpkg and apt would have
to be changed. However, that is not my proposal at all. I don't intend
to create a w32-i586 Debian distribution which must also accept w32-i386
packages. I want to create an entire w32-i586 distribution.
(well, currently, I just want to provide cross compiling packages for
such a platform)
I also heard about people who compiled a whole (Debian based) system
for i586 to increase the overall performance of their system. They,
too, had the same problem: How to name this architecture/cpu? As far
as I remember, they "solved" that problem by adding a "pentium" line
(or similar, AFAIR) to their cputable.
Thus, I don't think it is the question whether one wants to compile
for i586, i686, etc. There are always good reasons for some groups to
do so. IMHO, the more important question is how to name that thing. So
it would be very nice if dpkg-architecture would be flexible enough to
support that, instead of stepping in the way.
To solve the problem at least for cross compiling, there are two
possible ways to go:
1) insert more CPU types into dpkg-architecture
2) handle an extra CPU list internally by dpkg-cross
(e.g. when cross compiling for w32-i586, create a package
While option 2) is a huge amount of work for dpkg-cross,
option 1) is relatively easy to do in dpkg.
In addition, 1) opens the way for apt to support optimized
binaries natively in the future, and also to use dpkg-cross
for optimized packages, instead of additional debian/rules
Optimized and cross compiles packages are not that different, IMHO.
This mail goes to:
* debian-devel mailing list,
(to see if there's a general consensus)
* debian-embedded mailing list,
(because here the thread started)
* debian-dpkg mailing list,
(because it affects the future of dpkg/apt)
* Dpkg Developers
(because this discussion affects dpkg-architecture)
This mail is a summary of the discussions on the debian-embedded mailing
list. Thread overview:
In particular, please have a look at these postings: