* register long sp asm("r1") incorrect
@ 2010-02-09 15:24 Pavel Machek
2010-02-11 5:31 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 8+ messages in thread
From: Pavel Machek @ 2010-02-09 15:24 UTC (permalink / raw)
To: benh, paulus, linuxppc-dev, kernel list
...according to gcc docs, sp should be global, or placement in
register is not guaranteed (except at asm boundaries, but there are
none).
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-09 15:24 register long sp asm("r1") incorrect Pavel Machek
@ 2010-02-11 5:31 ` Benjamin Herrenschmidt
2010-02-15 7:34 ` Pavel Machek
0 siblings, 1 reply; 8+ messages in thread
From: Benjamin Herrenschmidt @ 2010-02-11 5:31 UTC (permalink / raw)
To: Pavel Machek; +Cc: linuxppc-dev, paulus, kernel list
On Tue, 2010-02-09 at 16:24 +0100, Pavel Machek wrote:
> ...according to gcc docs, sp should be global, or placement in
> register is not guaranteed (except at asm boundaries, but there are
> none).
Sorry I'm not sure I grok what you mean.
Cheers,
Ben.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-11 5:31 ` Benjamin Herrenschmidt
@ 2010-02-15 7:34 ` Pavel Machek
2010-02-15 19:59 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 8+ messages in thread
From: Pavel Machek @ 2010-02-15 7:34 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: linuxppc-dev, paulus, kernel list
> On Tue, 2010-02-09 at 16:24 +0100, Pavel Machek wrote:
> > ...according to gcc docs, sp should be global, or placement in
> > register is not guaranteed (except at asm boundaries, but there are
> > none).
>
> Sorry I'm not sure I grok what you mean.
Well, according to gcc doscs and my experience, local "register int
__asm()" variables only work by accident (or not at all).
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-15 7:34 ` Pavel Machek
@ 2010-02-15 19:59 ` Benjamin Herrenschmidt
2010-02-15 20:28 ` Pavel Machek
0 siblings, 1 reply; 8+ messages in thread
From: Benjamin Herrenschmidt @ 2010-02-15 19:59 UTC (permalink / raw)
To: Pavel Machek; +Cc: linuxppc-dev, paulus, kernel list
On Mon, 2010-02-15 at 08:34 +0100, Pavel Machek wrote:
> > On Tue, 2010-02-09 at 16:24 +0100, Pavel Machek wrote:
> > > ...according to gcc docs, sp should be global, or placement in
> > > register is not guaranteed (except at asm boundaries, but there
> are
> > > none).
> >
> > Sorry I'm not sure I grok what you mean.
>
> Well, according to gcc doscs and my experience, local "register int
> __asm()" variables only work by accident (or not at all).
Hrm... we definitely rely on that for our thread_info() access, and so
far it has worked well for us, but I'll poke our gcc folks just in case.
Cheers,
Ben.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-15 19:59 ` Benjamin Herrenschmidt
@ 2010-02-15 20:28 ` Pavel Machek
2010-02-15 21:04 ` Benjamin Herrenschmidt
0 siblings, 1 reply; 8+ messages in thread
From: Pavel Machek @ 2010-02-15 20:28 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: linuxppc-dev, paulus, kernel list
On Tue 2010-02-16 06:59:52, Benjamin Herrenschmidt wrote:
> On Mon, 2010-02-15 at 08:34 +0100, Pavel Machek wrote:
> > > On Tue, 2010-02-09 at 16:24 +0100, Pavel Machek wrote:
> > > > ...according to gcc docs, sp should be global, or placement in
> > > > register is not guaranteed (except at asm boundaries, but there
> > are
> > > > none).
> > >
> > > Sorry I'm not sure I grok what you mean.
> >
> > Well, according to gcc doscs and my experience, local "register int
> > __asm()" variables only work by accident (or not at all).
>
> Hrm... we definitely rely on that for our thread_info() access, and so
> far it has worked well for us, but I'll poke our gcc folks just in case.
Thanks, and let me know about any results.
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-15 20:28 ` Pavel Machek
@ 2010-02-15 21:04 ` Benjamin Herrenschmidt
2010-02-15 22:15 ` H. Peter Anvin
0 siblings, 1 reply; 8+ messages in thread
From: Benjamin Herrenschmidt @ 2010-02-15 21:04 UTC (permalink / raw)
To: Pavel Machek; +Cc: linuxppc-dev, paulus, kernel list
On Mon, 2010-02-15 at 21:28 +0100, Pavel Machek wrote:
> On Tue 2010-02-16 06:59:52, Benjamin Herrenschmidt wrote:
> > On Mon, 2010-02-15 at 08:34 +0100, Pavel Machek wrote:
> > > > On Tue, 2010-02-09 at 16:24 +0100, Pavel Machek wrote:
> > > > > ...according to gcc docs, sp should be global, or placement in
> > > > > register is not guaranteed (except at asm boundaries, but there
> > > are
> > > > > none).
> > > >
> > > > Sorry I'm not sure I grok what you mean.
> > >
> > > Well, according to gcc doscs and my experience, local "register int
> > > __asm()" variables only work by accident (or not at all).
> >
> > Hrm... we definitely rely on that for our thread_info() access, and so
> > far it has worked well for us, but I'll poke our gcc folks just in case.
>
> Thanks, and let me know about any results.
All the gcc folks I talked to say something along the lines that there
is no way in hell it doesn't work :-)
It's true that most other use of it we have are global scope (local_paca
in r13, glibc use of r2/r13, etc...) afaik, but since r1 itself is the
stack pointer always, I think they pretty much guarantee it works.
I'm CCing a couple of experts just to be sure.
Cheers,
Ben.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-15 21:04 ` Benjamin Herrenschmidt
@ 2010-02-15 22:15 ` H. Peter Anvin
2010-02-18 22:57 ` Pavel Machek
0 siblings, 1 reply; 8+ messages in thread
From: H. Peter Anvin @ 2010-02-15 22:15 UTC (permalink / raw)
To: Benjamin Herrenschmidt; +Cc: kernel list, linuxppc-dev, paulus, Pavel Machek
On 02/15/2010 01:04 PM, Benjamin Herrenschmidt wrote:
>
> It's true that most other use of it we have are global scope (local_paca
> in r13, glibc use of r2/r13, etc...) afaik, but since r1 itself is the
> stack pointer always, I think they pretty much guarantee it works.
>
It should work, because r1, being the stack pointer, is already marked a
reserved register in gcc.
The reference Pavel is citing bascially states that gcc won't globally
reserve the register, which is true, but it is already reserved anyway.
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: register long sp asm("r1") incorrect
2010-02-15 22:15 ` H. Peter Anvin
@ 2010-02-18 22:57 ` Pavel Machek
0 siblings, 0 replies; 8+ messages in thread
From: Pavel Machek @ 2010-02-18 22:57 UTC (permalink / raw)
To: H. Peter Anvin; +Cc: kernel list, linuxppc-dev, paulus
On Mon 2010-02-15 14:15:17, H. Peter Anvin wrote:
> On 02/15/2010 01:04 PM, Benjamin Herrenschmidt wrote:
> >
> > It's true that most other use of it we have are global scope (local_paca
> > in r13, glibc use of r2/r13, etc...) afaik, but since r1 itself is the
> > stack pointer always, I think they pretty much guarantee it works.
> >
>
> It should work, because r1, being the stack pointer, is already marked a
> reserved register in gcc.
>
> The reference Pavel is citing bascially states that gcc won't globally
> reserve the register, which is true, but it is already reserved anyway.
Ok, thanks for clarification.
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2010-02-19 19:36 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
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2010-02-09 15:24 register long sp asm("r1") incorrect Pavel Machek
2010-02-11 5:31 ` Benjamin Herrenschmidt
2010-02-15 7:34 ` Pavel Machek
2010-02-15 19:59 ` Benjamin Herrenschmidt
2010-02-15 20:28 ` Pavel Machek
2010-02-15 21:04 ` Benjamin Herrenschmidt
2010-02-15 22:15 ` H. Peter Anvin
2010-02-18 22:57 ` Pavel Machek
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