V850 ABI?

V850 ABI?

[Torsten Mohr]

Hi,

from gcc-3.4.4/gcc/config/v850/v850.h i got some ideas
about the registers (#defs REGISTER_NAMES and
ADDITIONAL_REGISTER_NAMES) and about the use of them
from the comments to #def REG_ALLOC_ORDER.

In that file i've also read about an option "ghs", does
that one switch to the Greenhills ABI?

From that file i can't really conclude everything.
For example i don't know if registers 20 and 21 hold the
values 255 and 65535 (an optimisation on V850).  The startup
code in newlib assigns them, but does gcc really rely on that
and uses that (this question is just an example)?


Is there a description of the ABI or the ABIs available?


Best regards,
Torsten.

Re: V850 ABI?

[James E Wilson]

Torsten Mohr wrote:
> In that file i've also read about an option "ghs", does
> that one switch to the Greenhills ABI?

In theory, yes.  In practice, I'd be skeptical.  It probably hasn't been
well tested.

> From that file i can't really conclude everything.
> For example i don't know if registers 20 and 21 hold the
> values 255 and 65535 (an optimisation on V850).  The startup
> code in newlib assigns them, but does gcc really rely on that
> and uses that (this question is just an example)?

Try writing a simple example program to check.  Since 20 and 21 are not
fixed registers, my guess would be no.

> Is there a description of the ABI or the ABIs available?

Red Hat probably has a manual.  If you can find a copy of a Red Hat v850
release, there may be a manual inside it that has ABI info.  Otherwise,
probably no.

Gcc normally does not define the ABI.  We just follow ABI standards
produced by others.  You could try checking in NEC publishes an ABI for
the v850.

For some embedded targets, gcc defines the ABI because there isn't an
external one we can follow.  In this case, gcc should document the ABI
that it implements.  This is done for some targets.  If you look, you
can see that some targets have a *ABI* or *abi* file that documents the
gcc abi.  Unfortunately, we don't do this for as many targets as we should.
-- 
Jim Wilson, GNU Tools Support, http://www.specifix.com