svn commit: r340676 - in head/sys: kern sys

[Mateusz Guzik]

On 11/20/18, Warner Losh <imp at bsdimp.com> wrote:
> On Tue, Nov 20, 2018 at 8:28 AM Mateusz Guzik <mjguzik at gmail.com> wrote:
>
>> On 11/20/18, Konstantin Belousov <kostikbel at gmail.com> wrote:
>> >> +#if defined(__mips__) || defined(__powerpc__)
>> > Please note what I asked about this #ifdefs in the review. mips
>> > and powerpc machine/atomic.h should define some symbol like
>> > __ATOMIC_NO_64_OPS and this case should be handled in less
>> > arch-explicit
>> > manner.
>> >
>>
>> Right, should have mentioned that in the commit message.
>>
>> Anyhow, mips has some degree of 64 bit ops even for 32 bits so
>> this becomes more iffy. In particular it does have atomic_add_64.
>> I don't have a good way to test mips atomics and since non-atomic
>> version for powerpc was needed anyway I decided not to try to
>> add one.
>>
>
> I thought the 64-bit stuff was not present in true 32-bit mips at all. You
> need the lld/scd instructions to do 64-bit atomics which are only available
> in a 64-bit environment (eg n32 or n64 execution).  They throw a fatal
> machine error if you execute them in o32 land.
>
> And I think the proper ifdef for this is defined(mips) &&
> !defined(__mips_n64) && !defined(__mips_n32) or something horrible like
> that to not pessimize 64-bit executions.
>

And powerpc will require something of similar sort (as reported by Mark
MIllard). It gets quite ugly indeed.

I don't have strong opinion how to express the ifdefs, I think this is least
bad if sticking to a mi header:

diff --git a/sys/sys/systm.h b/sys/sys/systm.h
index a1b98c5660c..fab94ee7979 100644
--- a/sys/sys/systm.h
+++ b/sys/sys/systm.h
@@ -523,7 +523,11 @@ int alloc_unr_specific(struct unrhdr *uh, u_int item);
 int alloc_unrl(struct unrhdr *uh);
 void free_unr(struct unrhdr *uh, u_int item);

-#if defined(__mips__) || defined(__powerpc__)
+#if defined(mips) && !defined(__mips_n64) && !defined(__mips_n32)
+#define UNR64_LOCKED
+#endif
+
+#if defined(__powerpc__) && !defined(__powerpc64__)
 #define UNR64_LOCKED
 #endif


-- 
Mateusz Guzik <mjguzik gmail.com>