mpc8xx and ld.so problem

[Yuli Barcohen]

>>>>> Marcelo Tosatti writes:

    Yuli> [...deleted...]

    Jason> Ha. Funny. The glibc powerpc maintainer doesn't want any
    Jason> embedded fixes in the mainline. Last I checked, that was for
    Jason> 'the tools vendors' to fix.

    Jason> "We won't work around processor bugs" is their philosophy.

    Yuli> [...deleted...]

    Yuli> I investigated the problem a bit when I had trouble with a
    Yuli> self-compiled glibc a year or so ago. IIRC, I found bug in the
    Yuli> memset code, not in the chip. The code was just wrong for
    Yuli> cache line sizes not equal to 32. So memset.S is good for 60x
    Yuli> series (PQII included) but for 8xx it fails.

    Marcelo> I suppose you didnt actually use dcbz for userspace memset
    Marcelo> on 8xx?

Standard glibc did. After the fix, it doesn't do it any more on our
systems.

    Yuli> We use dcbX instructions in some kernel drivers and since we
    Yuli> never had any problems with those drivers I'm a bit surprised
    Yuli> to hear that all 8xx chips have got that bug.

    Marcelo> The problem is that the DAR register is correctly unset (it
    Marcelo> comes as NULL IIRC) on pagefaults for the dcbz
    Marcelo> instruction. The dcbz instructions you issue are probably
    Marcelo> always works on kernel addresses whose pagetables are
    Marcelo> present?

It's not dcbz, it's dcbi/dcbf. And yes, they work on kernel addresses. I
never investigated if the page tables are present or not because there
were no problems.

    Marcelo> Joakim has developed a workaround for the
    Marcelo> problem... although I promised him several times to test it
    Marcelo> I never managed to get dcbz to work on the kernel copying
    Marcelo> functions. :(

[...patch deleted...]

Well, if I manage to find time, I'll try it. No timetables though. I'm
not sure if using dcbz in user-space memset is such a great
optimisation. It well can be an example of over-engineering.

-- 
========================================================================
 Yuli Barcohen       | Phone +972-9-765-1788 |  Software Project Leader
 yuli at arabellasw.com | Fax   +972-9-765-7494 | Arabella Software, Israel
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