register long sp asm("r1") incorrect

register long sp asm("r1") incorrect

[Pavel Machek]

...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

Re: register long sp asm("r1") incorrect

[Benjamin Herrenschmidt]

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.

Re: register long sp asm("r1") incorrect

[Pavel Machek]

> 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

Re: register long sp asm("r1") incorrect

[Benjamin Herrenschmidt]

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.

Re: register long sp asm("r1") incorrect

[Pavel Machek]

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

Re: register long sp asm("r1") incorrect

[Benjamin Herrenschmidt]

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.

Re: register long sp asm("r1") incorrect

[H. Peter Anvin]

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.

Re: register long sp asm("r1") incorrect

[Pavel Machek]

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