bootloader & head.S weirdness & restructuring

Wolfgang Denk wd at
Fri Nov 26 23:06:21 EST 1999

In message <Pine.LNX.4.10.9911261032590.22448-100000 at>
Michael Schmitz wrote:

> > > >     #if defined(CONFIG_x) || defined(CONFIG_y) || defined(CONFIG_z)
> > > >     ...
> > > >     #endif
> Plus it has the added benefit that you can still build kernels that
> support a range of hardware (by making has_feature_a not const 0 or 1 but
> something like feature_present(a) :-) If you don't need this, both are
> equivalent though. 

This depends if the compiler has a chance to  decide  which  code  is
needed and which not. Otherwise it cannot optimize away dead code.

> Worried about wasting a few cycles on the branch? I've never noticed a

No, it's the code size that matters on  many  embedded  systems.  The
target  is  a minimal kernel code size. And improved performance is a
most welcome add-on.

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at
" of the main causes of the fall of the Roman Empire was  that,
lacking  zero,  they had no way to indicate successful termination of
their C programs."                                     - Robert Firth

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