[Clfs-dev] startfile_prefix_spec

[Joe Ciccone]

On 02/03/2011 01:41 AM, DJ Lucas wrote:
> On 02/02/2011 11:24 PM, DJ Lucas wrote:
>> IIUC, it seems to me that startfile_prefix_spec should be defined as
>> /usr/lib64 on x86_64 in CLFS, as the relative path used is "." if no
>> -m flags are supplied. 
> Never mind that, I answered my own question, no bug. Upon further
> reading, IIUC, *multilib_defaults is m64 so the first case is never
> used (is <blank> the correct option for the first case?). If that is
> correct the path could be /usr/share/, /usr/bin/, or
> /usr/<insert_any_existing_directory_here>/, as long as it makes the
> relative path work. So there is no error, however, see the next
> question below...
>> I'm trying to wrap my head around multi-lib and how all of the pieces
>> fit together. Does ld later override these paths, or am I completely
>> missing the point here? Is there some justification for using
>> /usr/lib that I haven't found yet?
>
> The related question:
>
> Why not:
> ----------
> *multilib:
> . !m64 !m32;64:lib64 m64 !m32;32:lib !m64 m32;
> ----------
> *multilib_defaults:
> m64
> ----------
> *startfile_prefix_spec:
> /usr/
> ----------
>
>
Because that would be broken,
/usr/./crti.o would yield a broken path and packages wouldn't compile
unless you explicitly set -m32 or -m64.

See my previous email.
>
> I've been digging and I can't find a good reason why the relative
> paths are used. I had suspected that it dates back to the original
> addition of *startfile_prefix_spec (early multilib days?), but have
> found nothing as for why. A good rationale could probably result in
> some nice explanatory text in both CLFS and LFS as a result if anybody
> has an answer.
>
The relative paths are used for a lot more then just the startfile
prefix. You can also use it to calculate lib dirs in your build system.
There are a select number of build systems that use this. GCC uses these
relative paths for almost all of its paths calcs.

# gcc -print-multi-os-directory
../lib64
# gcc -print-multi-os-directory -m32
../lib
# gcc -print-multi-os-directory -m64
../lib64


-- 
Joe Ciccone