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Re: how to support 32- & 64-bit versions of libraries


Thanks very much for the succinct lesson on biarch and multiarch.

On Wed, Mar 18, 2009 at 07:31:18PM +0100, Goswin von Brederlow wrote:

> If you want to support 64bit (and n32) gmp on ppc, s390, sparc, mips
> and mipsel NOW then look at zlib as an example.

Great.  So I've gone through the zlib example in some detail, along
with the solutions provided by Matthias K. and Bill A.  Inspired by
zlib, I figured I might as well build lib32xxx and lib64xxx wherever
possible, rather than just on amd64 and ppc, respectively.  

I'd greatly appreciate it if interested parties would have a look
at what I've done [1] and offer constructive criticism.

I've run into a roadblock, however, in that the header gmp.h is
generated by configure.  It has some parameters (size of a limb) that
depend on whether compiled for 32 or 64 bits.  So on amd64, for
example, I have two incompatible gmp.h files.  Matthias provided a
gmp.h wrapper from Redhat that selects between architecture variants
based on preprocessor symbols, e.g.

    #if defined(__i386__)
    #include "gmp-i386.h"
    #elif defined(__ia64__)
    #include "gmp-ia64.h"

However, in the case at hand it is the same architecture.  One
variant is compiled with -m32 and the other with -m64.  Is there a
symbol that can distinguish the two so that I can use the Redhat
trick?  Other solutions?

Incidentally, the zlib debian/rules uses "gcc -m64" on architectures
s390, sparc, i386, and powerpc.  The info page on compiler options for
gcc 4.3, however, says:

     These `-m' switches are supported in addition to the above on AMD
     x86-64 processors in 64-bit environments.

         Generate code for a 32-bit or 64-bit environment.  The 32-bit
         environment sets int, long and pointer to 32 bits and
         generates code that runs on any i386 system.  The 64-bit
         environment sets int to 32 bits and long and pointer to 64
         bits and generates code for AMD's x86-64 architecture. For
         darwin only the -m64 option turns off the `-fno-pic' and
         `-mdynamic-no-pic' options.

Does it really work to use -m64 on an i386?  Does amd64 code result?


[1] http://svn.debian.org/wsvn/pkg-scicomp/gmp/trunk/?rev=0&sc=0

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