Re: [PATCH 9/24] make atomic_read() behave consistently on ia64

Chris Snook
2007-08-10T22:44:03Z

Luck, Tony wrote:
>> Use atomic64_read to read an atomic64_t.
>
> Thanks Andreas!
>
> Chris: This bug is why the 8-byte loads got changed to 4-byte + sign-extend
> by your change to atomic_read().

I figured as much. Thanks for confirming this.

> With this applied together with shuffling the volatile from the
> declaration to the usage (in both atomic_read() and atomic_set()
> the generated code *almost* reverts to the original.
>
> There are some differences where ld4 have turned into ld8 though.
> Are these bugs in the use of atomic_add() and atomic_sub(). E.g.
> the first of these changes is in: ipc/msg.c:freeque() where we have:
>
> atomic_sub(msg->q_cbytes, &msg_bytes);
>
> Now the type of msg->q_cbytes is "unsigned long" ... so it seems a
> poor idea to subtract such a large typed object from "msg_bytes"
> which is a mere slip of an atomic_t.
>
> Or is there some other type-wrangling that needs to happen in
> include/asm-ia64/atomic.h? There are a total of nineteen of
> these ld4->ld8 transforms.

Possibly. Either that or we've uncovered some latent bugs. Maybe a
combination of the two. Can you list those 19 changes so we can
evaluate them? I'm told there were some *(volatile *) bugs fixed in gcc
recently, so it's also possible your 3.4.6 is showing those. I can test
that on a more recent gcc on ia64 if it's inconvenient for you to do so
on your test box.

-- Chris