Differences in headers between i386 and x86_64

[Miloslav Trmač]

Hello,
The attached script searches for differences between C/C++ header files
in RPM sets for different architectures, in order to examine
one group of issues arising when attempting to compile software for i386
on x86_64.

In the ideal world it would be possible to just install i386 *-devel
packages on x86_64 and compile using gcc -m32 or whatever the
correct command is. This can only work if the devel packages do not
conflict in their header files.


The full results for today's rawhide are available at
http://people.redhat.com/mitr/diffincludes/diff-20040806.bz2
They are quite large because of some false positives; you can
get a much smaller diff by s/diff -urN/diff -ur/ in the script,
but watching file list differences has already helped find one
incompatibility. Therefore I have left it this way, which means that
the most common reason of large diffs is a package already prepared
for cross-arch compilation :)

A summary report (without the false positives and differences created by
build timestamps entered in header files) is attached.

The good news is that 271 out of the 345 packages containing header files
contain no header file differences.


Generally the most common reason of differences is including a "config.h"
file generated by autoconf or something similar; in cases where the config
values are architecture specific, the following are common among several
packages:
- duplicating the functionality of <stdint.h> or <inttypes.h>
  (definitions of "int64", printf/scanf formats, ...)
- SIZEOF_type, ALIGNOF_type
- VA_LIST_IS_ARRAY
- _FILE_OFFSET_BITS, _LARGEFILE_SOURCE

I have not examined the packages to find out whether the values are
used in other header files at all. Even if they are not, they might
unfortunately be used in applications:
	#include <libart.h>
	#if ART_SIZEOF_LONG ...


Another thing I currently don't know anything about is how does pkg-config
fit into this picture; when compiling for i386, it should point to the
32-bit libdir (which will automatically cause the correct glib config
file to be included, for instance). Similar issues arise with QTDIR
and the mechanism perl or xemacs plugins use for finding libraries
and header files.

The summary contains affected files for each package and in some cases notes
about differences I have found curious or somehow special; such note
does not imply this is the only difference in the header files; when in
doubt, look at the complete output.
	Mirek

[Ralf Corsepius]

On Sat, 2004-08-07 at 05:04, Miloslav Trmac wrote:

>  In the ideal world it would be possible to just install i386 *-devel
>  packages on x86_64 and compile using gcc -m32 or whatever the
>  correct command is. This can only work if the devel packages do not
>  conflict in their header files. 

>  Generally the most common reason of differences is including a
> "config.h"
>  file generated by autoconf or something similar; in cases where the config
>  values are architecture specific, the following are common among several
>  packages:
>  - duplicating the functionality of <stdint.h> or <inttypes.h>
>    (definitions of "int64", printf/scanf formats, ...)
>  - SIZEOF_type, ALIGNOF_type
>  - VA_LIST_IS_ARRAY
>  - _FILE_OFFSET_BITS, _LARGEFILE_SOURCE 
Such cases are a strong indication for these packages using broken
configure scripts
cf. http://lists.gnu.org/archive/html/autoconf/2004-08/msg00019.html
(http://lists.gnu.org/archive/html/autoconf/2004-08/msg00009.html)

Ralf