[Gc] Re: Powerpc/m68k issue running test_stack

Thorsten Glaser tg at mirbsd.de
Wed Nov 21 10:51:11 PST 2012

Hi Ivan,

sorry for my three a bit disoriented quick posts. I had wanted
to do some “quick” tests, and then, thinking that was “it”,
posted the results, but got something new after each message ☹

Ivan Maidanski dixit:

>Could you summarize please you suggestion how to fix this?

I need to make a couple more checks. *Maybe* it got fixed
with the new eglibc patch already, since the Debian package
7.3~alpha3+git20121114-1 unexpectedly *passed* all its tests.

So, right now, do nothing.

>Use GCC builtins for AO_test_and_set_full and AO_compare_and_swap_full
>for m68k if GCC 4.6+, right?

The GCC builtins can be used on m68k if *all* of these two
conditions are matched:
• GCC 4.6 or above
• a link-time check with the functions passes, to weed
  out GCC builds that do not yet have the patch to add
  these functions
• a Linux kernel with certain bugs fixed, no non-Linux
  (I can dig out exact versions if you want, but for
  now, roughly 3.2 or up should work)

However, it’s slower in all cases. I’m Cc’ing the porter
list so the Debian and Linux kernel people can say whether
they think that libatomic-ops should continue to use CAS
and friends, or switch to the kernel function if available.

The Linux kernel version check is run-time, but honestly,
if it’s there at compile time it’ll be there at run-time
too, besides GCC and others use the kernel helper as well
nowadays. A non-Linux kernel can't use them, though.

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stupidity in its gene-pool[…]never eradicated[…]magic evens the odds that way.
It's[…]harder to die for us than[…]muggles[…]wonder if, as technology[…]better
[…]same will[…]happen there too. Dursleys' continued existence indicates so.

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