Re: Debian ports for RiscPC, ARM710, etc.
Jim Pick wrote:
>
> I'm wondering what we should do for the Debian port to support more
> machines than just the NetWinder.
>
> Right now, we've built gcc with the --with-cpu=strongarm option, and
> we are compiling all the packages with the normal CFLAGS options.
> We're using the Corel patched gcc right now, but plan on moving to
> Philip's egcs.
>
> So I suppose we are building binaries that use the halfword
> instructions. Is that correct?
Yes. They are automatically enabled with -mcpu=strongarm. The NetWinder
requires -march=armv4 to ensure some cpu cache issues are handled correctly,
however, the cpu could be left as default.
> In the interests of portability, what would be the performance cost if
> we somehow compiled things without the halfword instructions? Do all
> apps benefit, or just some specific ones? Corel is using them for
> their RPM-based distribution, so I have assumed that there is a
> significant performance difference.
Not in my experience. The halfword and signed byte instructions are only
emitted with -O2. The basic code generator does not emit them, only the
optimizing pass.They are used to speed up access to shorts, and signed
characters if I remember correctly. They do speed things up, it takes
one two cpu cycles to access shorts without them and three to access
signed bytes if I recall correctly.
I chose to configure gcc with -with-cpu=strongarm to generate code that
would be most efficient on the NetWinder.
Scott
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