multilib question

Ralf Corsepius ralf.corsepius at
Thu Nov 10 06:47:26 UTC 2005

On Wed, 2005-11-09 at 22:06 -0800, Till Straumann wrote:
> I want to build gcc/newlib with the following variants:
> -mcpu=860 -soft-float
> -mcpu=603e -Dmpc8260
> -mcpu=604
> -mcpu=7400 -mabi=altivec -maltivec -mvrsave=yes
> -mcpu=7400 -mabi=altivec -maltivec -mvrsave=no
> -mcpu=7400 -mabi=altivec -mno-altivec
> how do I have to set the MULTILIB_xxx variables in 't-rtems' ?
It's documented in

Search for MULTILIB*, the documentation is spread across several
chapters. Also, check gcc/config/rs6000/rs6000.[ch], there are other
macros being involved (compiler defaults and implicit flags)

The details of how to achieve your objective are far from being trivial
and beyond the scope of this list. It's not possible to answer this in
one sentence.

The brute force approach would be:
Set up a vector of compiler flags containing _all_ flags being used.
Then expand all possible permutations of this vector. Afterwards start
minimizing the resulting matrix by applying MULTILIB_* rules.

An easier approach would be to start with the existing t-rtems and to
try gradually adding one variant after the other. This way you at least
avoid side-effects you might not be aware about (e.g. the implicit
defaults of the default multilib variant - It's missing from your list
above and often not visible in t-* files)


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