Re: clear_cache on Alpha architecture not implemented?

[Camm Maguire <camm at maguirefamily dot org>]

Greetings, and thanks for this very helpful synopsis.

I'm wondering if there is a simple configure time test to detect when
this has been fixed.  If I just aborted using __builtin___clear_cache if
it is in fact a noop on alpha, ppc, ppc64, and ia64, would this suffice?

Take care,

Richard Henderson <rth@redhat.com> writes:

> On 05/03/2012 10:51 AM, Camm Maguire wrote:
>> The goal was to exercise the very helpful gcc __builtin___clear_cache
>> support, and to avoid having to maintain our own assembler for all the
>> different cpus in this regard.  Clearly, it is easy to revert this on a
>> per architecture basis if absolutely necessary.  If gcc does or does not
>> plan on fixing this, please let me know so gcl can adjust as needed.
>
> While we can probably fix this, you should know that __builtin_clear_cache
> is highly tied to the implementation of trampolines for the target.  Thus
> there are at least 3 targets that do not handle this "properly":
>
> For alpha, we emit imb directly during the trampoline_init target hook.
>
> For powerpc32, the libgcc routine __clear_cache is unimplemented, but the
> cache flushing for trampolines is inside the __trampoline_setup routine.
>
> For powerpc64 and ia64, the ABI for function calls allows trampolines to
> be implemented without emitting any insns, and thus the icache need not be
> flushed at all.  And thus we never bothered implementing __builtin_clear_cache.
>
> So, the fact of the matter is that you can't reliably use this builtin for
> arbitrary targets for any gcc version up to 4.7.  Feel free to submit an
> enhancement request via bugzilla so that we can remember to address this
> for gcc 4.8.
>

-- 
Camm Maguire			     		    camm@maguirefamily.org
==========================================================================
"The earth is but one country, and mankind its citizens."  --  Baha'u'llah