Re: WAW and RAW warnings in kernel build
Just because I'm lazy, I'd appreciate a copy of the .s file :).
There have been a couple of bugs around predication in the past,
too.
On Tue, 2003-08-05 at 15:36, Richard Harke wrote:
> Before trying to locate the precise lines in the kernel, I tried
> an experiment. I I took a small routine in assembly
> from the book "IA64 and Elementary Functions" (page 36) and
> assembled it. I got several WAW warnings. All the instructions
> involved are predicated with it arranged that only one
> predicate will be true. But apparently the assembler can't detect that.
> I don't know how much the assembler tries to do in this case
> but appears to me to be non-trivial. This case involves four
> predicates all set on the same pass in a loop. But the tests that
> set them are controlled by two more predictates that are set
> on a previous pass. And the numbers have changed because
> of register rotation.
>
> I can stil try to find the lines in question in the kernel, if anybody
> thinks that would be useful. Also, I could email a copy of the
> routine described above.
>
> Richard
>
> On Tuesday 05 August 2003 09:19 am, Al Stone wrote:
> > If someone will send me the snippets of code
> > with the warnings, I'll take a look at both the code
> > and gas to see what it's doing....
> >
> > On Mon, 2003-08-04 at 15:04, David Mosberger wrote:
> > > >>>>> On Mon, 4 Aug 2003 10:03:50 -0600, Bjorn Helgaas
> > > >>>>> <bjorn.helgaas@hp.com> said:
> > >
> > > Bjorn> They've been there for years, so I've learned to ignore them.
> > >
> > > I wouldn't want to encourage people to ignore those messages. Yes,
> > > some of them can be ignored, but if you develop new assembly code, I'd
> > > definitely pay attention.
> > >
> > > Unfortunately, GCC sometimes doesn't provide sufficient annotation to
> > > the assembler so that it could know that the offending code is indeed
> > > safe.
> > >
> > > Also, in the hand-coded assembly routines, there are a few places
> > > where hazard warnings are a bit difficult to avoid. It's something we
> > > should fix eventually, but it may require some help from gas.
> > >
> > > --david
--
Ciao,
al
----------------------------
Al Stone
Linux & Open Source Lab
Hewlett-Packard Company
Phone: 970-898-0345
Telnet: 898-0345
Fax: 970-898-3804
E-mail: ahs3@fc.hp.com
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