lkml.org 
[lkml]   [2007]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH 0/24] make atomic_read() behave consistently across all architectures
Date
>>>> atomic_dec() writes
>>>> to memory, so it _does_ have "volatile semantics", implicitly, as
>>>> long as the compiler cannot optimise the atomic variable away
>>>> completely -- any store counts as a side effect.
>>>
>>> I don't think an atomic_dec() implemented as an inline "asm volatile"
>>> or one that uses a "forget" macro would have the same re-ordering
>>> guarantees as an atomic_dec() that uses a volatile access cast.
>>
>> The "asm volatile" implementation does have exactly the same
>> reordering guarantees as the "volatile cast" thing,
>
> I don't think so.

"asm volatile" creates a side effect. Side effects aren't
allowed to be reordered wrt sequence points. This is exactly
the same reason as why "volatile accesses" cannot be reordered.

>> if that is
>> implemented by GCC in the "obvious" way. Even a "plain" asm()
>> will do the same.
>
> Read the relevant GCC documentation.

I did, yes.

> [ of course, if the (latest) GCC documentation is *yet again*
> wrong, then alright, not much I can do about it, is there. ]

There was (and is) nothing wrong about the "+m" documentation, if
that is what you are talking about. It could be extended now, to
allow "+m" -- but that takes more than just "fixing" the documentation.


Segher

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-08-18 02:11    [W:0.305 / U:5.404 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site