Re: Show stopper bugs for 5.0

[Michael Lorenz <macallan%netbsd.org@localhost>]

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Hello,

On May 20, 2008, at 19:58, Tim Rightnour wrote:

> On 20-May-2008 Michael Lorenz wrote:
> > - - at least on my 2x 7400 I need additional cache flushes in ld.so,
> > otherwise the CPU occasionally tries to use reloc entries not yet
> > written into memory which leads to userland crashes. Doesn't seem to
> > happen with 745x CPUs, others with 7400s have reported the same
> > problem. I'll check if it still happens, if it does we'll need to
> > think about a proper solution here.
>
> Whats the rationale for not adding those cache flushes in?  Does it  
> cause a
> significant slowdown?  If so, how much?  Would you be willing to run a
> bytebench with and without the fix and post the results?  If its a  
> minor
> slowdown, I'm inclined to just do it, maybe with an option to disable?

I didn't commit the fix yet because chuq thinks that's just a  
workaround for a problem elsewhere, but I couldn't find anything  
remotely related in the 7400 errata list. He's got a dual 7455 which  
doesn't have this problem - his CPUs have L3 cache though, no idea if  
that's significant. I doubt the slowdown is even measurable - it only  
happens when something loads a shared object.

The patch I'm using right now is this:
Index: ppc_reloc.c
===================================================================
RCS file: /cvsroot/src/libexec/ld.elf_so/arch/powerpc/ppc_reloc.c,v
retrieving revision 1.40
diff -u -w -r1.40 ppc_reloc.c
- --- ppc_reloc.c 23 May 2006 16:27:41 -0000      1.40
+++ ppc_reloc.c 21 May 2008 00:38:23 -0000
@@ -239,7 +239,7 @@
                 * in _rtld_setup_pltgot() after all the entries  
have been
                 * initialized.
                 */
- -               /* __syncicache(where - 3, 12); */
+               __syncicache(where - 3, 12);
        }

        return 0;

have fun
Michael


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