On Thu, Mar 14, 2002 at 03:37:38PM +1100, Rusty Russell wrote:
> > I am also a bit concerned however about aliasing that the compiler
> > might not detect. For example, with this code:
> >
> > this_cpu(foo) = 13;
> > per_cpu(foo, 0) = 15;
> > printf("foo=%d\n", this_cpu(foo);
> >
> > might print the wrong value if gcc thinks that the first and second
> > assignment never alias each other. Does HIDE_RELOC() take care of
> > this also?
>
> I'd be pretty sure the compiler can't assume that. Richard would
> know...
I can't think of a way your current code is invalid. It's all
hidden behind an asm. The compiler could guess the two addresses
are the same iff smp_processor_id() is the constant 0, aka UP.
> > On a side-note, would you mind moving __per_cpu_data from smp.h into
> > compiler.h? I'd like to use it in processor.h and from that file, I
> > can't include smp.h due to a recursive dependency.
This definitely needs to be per-architecture. On Alpha, I think I
can use the Thread Local Storage model to be added to binutils 2.13
(and potentially compiler support to gcc 3.[23]). IA-64 may be able
to do the same. It's certain that x86 can't, since the userland
model requires %gs:0 point to the thread base, and the kernel folk
would never cotton to the segment swapping that would be needed.
r~
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This archive was generated by hypermail 2b29 : Fri Mar 15 2002 - 22:00:17 EST