[lkml]   [2008]   [Apr]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC patch 23/27] Immediate Values - Powerpc Optimization NMI MCE support
Mathieu Desnoyers writes:

> * Paul Mackerras ( wrote:
> > Mathieu Desnoyers writes:
> >
> > > Use an atomic update for immediate values.
> >
> > What is meant by an "atomic" update in this context? AFAICS you are
> > using memcpy, which is not in any way guaranteed to be atomic.
> >
> > Paul.
> I expect memcpy to perform the copy in one memory access, given I put a
> .align 2
> before the 2 bytes instruction. It makes sure the instruction modified
> fits in a single, aligned, memory write.

My original question was in the context of the powerpc architecture,
where instructions are always 4 bytes long and aligned. So that's not
an issue.

> Or maybe am I expecting too much from memcpy ?

I don't think memcpy gives you any such guarantees. It would be quite
within its rights to say "it's only a few bytes, I'll do it byte by

If you really want it to be atomic (which I agree is probably a good
idea), I think the best way to do it is to use an asm to generate a
sth (store halfword) instruction to the immediate field (instruction
address + 2). That's on powerpc of course; I don't know what you
would do on other architectures.


 \ /
  Last update: 2008-04-17 02:37    [W:0.236 / U:0.720 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site