[U-Boot] [RFC PATCH v2] ARM: Avoid compiler optimization for usages of readb, writeb and friends.

Albert ARIBAUD
2010-12-21T12:51:51Z

Le 21/12/2010 13:35, Alexander Holler a ?crit :

> Hmm, is there actual somethinbg which should forbid the compiler to
> generate such code which rereads something? It might not be nice, but I
> don't think that it is forbidden for a compiler to do so. So the proper
> way to handle such, might be to use asm to avoid that the compiler
> touches that register.

Yes there is something that should prevent a compiler from inserting
reads: these accesses are to hardware, not memory, and may cause side
effects even on read (these could be acknowledges, for instance; I've
seen instances of that myself on some HW).

Another way to look at it is that the semantics of " *ptr = value " is a
pure write and should not result in a write-then-read.

> Regards,
>
> Alexander

Amicalement,
--
Albert.