[kaffe] XScale jthreads code

[Helmer Krämer]

On Sat, 18 Sep 2004 10:09:59 +0100
Peter Naulls <peter at chocky.org> wrote:

> In message <20040918110313.618ba619 at moose>
>           Helmer Krämer <hkraemer at freenet.de> wrote:
> 
> > > In any case, I recommend you find the true cause, and take away any code
> > > that checks for an XScale.
> > 
> > to avoid the confusion, we should probably remove the --enable-xscale
> > configure option and have a --with-native-fpu (or whatever) option
> > instead that would default to true on i386 but to false on arm. The
> > different SP_OFFSETs in config/arm/threads.h would then depend on
> > whether an fpu is available and not on whether kaffe is built for
> > an xscale. Does that make more sense?
> 
> No, this is still misleading.  The presense or otherwise of an FPU is
> irrelevant on ARM with respect to the code. My first recommendation
> remains to find out the exact cause of the differences that lead to this
> incorrect conclusion being made.    I also suggest making any comparison
> to i386 might just cloud the issue.

The unix-jthreads threads system uses setjmp/longjmp to switch between
different (java) threads. To do this, it has to extract the value of the
SP from a jmp_buf. On linux, the offset of the SP inside a jmp_buf depends
on the presence of an fpu (unless I misread the glibc sources). Therefore,
kaffe has to know whether an fpu is available, because otherwise it can't
get this offset right.

Regards,
Helmer