Re: [Gcl-devel] clear_cache on Alpha architecture not implemented?

[Camm Maguire]

Greetings!  As a followup, I should note that sh4 and hppa are also
broken.  I currently have this in configure.in

case $use in
     sh4*) ;; #FIXME
     hppa*) ;; #FIXME
     *) 
     AC_MSG_CHECKING(__builtin___clear_cache)
                AC_TRY_COMPILE([],
                               [void *v,*ve;
                                __builtin___clear_cache(v,ve);
                                ],
                                [AC_DEFINE(HAVE_BUILTIN_CLEAR_CACHE)
                                 AC_MSG_RESULT(yes)],
                                 AC_MSG_RESULT(no));;
esac

Perhaps I should just add alpha, powerpc, ppc64, and ia64 to the
exception list and deal with this in the future if memory serves.

Take care,


Richard Henderson <address@hidden> 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.
>
>
>
> r~
>
>
>
>

-- 
Camm Maguire                                        address@hidden
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