Re: [Qemu-devel] [PATCH v2] i386: Use #defines instead of magic numbers for CPUID cache information

[Eduardo Habkost]

On Fri, Aug 30, 2013 at 04:51:20PM +0200, Andreas Färber wrote:
> Am 27.08.2013 17:24, schrieb Eduardo Habkost:
> > This is an attempt to make the CPUID cache topology code clearer, by
> > replacing the magic numbers in the code with #defines, and moving all
> > the cache information to the same place in the file.
> > 
> > I took care of comparing the assembly output of compiling
> > target-i386/cpu.c before and after applying this change, to make sure
> > not a single bit was changed on cpu_x86_cpuid() before and after
> > applying this patch (unfortunately I had to manually check existing
> > differences, because of __LINE__ expansions on
> > object_class_dynamic_cast_assert() calls).
> > 
> > This even keeps the code bug-compatible with the previous version: today
> > the cache information returned on AMD cache information leaves (CPUID
> > 0x80000005 & 0x80000006) do not match the information returned on CPUID
> > leaves 2 and 4. The L2 cache information on CPUID leaf 2 also doesn't
> > match the information on CPUID leaf 2. The new constants should make it
> > easier to eventually fix those inconsistencies. All inconsistencies I
> > have found are documented in code comments.
> > 
> > Signed-off-by: Eduardo Habkost <address@hidden>
> > Reviewed-by: liguang <address@hidden>
> > ---
> > Changes v1 -> v2:
> >  * s/leafs/leaves/ on code comments
> > ---
> >  target-i386/cpu.c | 184 
> > +++++++++++++++++++++++++++++++++++++++++++++++-------
> >  1 file changed, 162 insertions(+), 22 deletions(-)
> 
> I think this is a good idea and the code looked sane, but it is unclear
> to me from v1 whether Li Guang has verified as part of his review that
> all the bits match the original ones or just that Coding Style and
> general idea is okay?
> 
> I'm therefore holding off applying this one for today's pull, waiting
> until either someone confirms Eduardo's results or I find the time to do
> so myself, the former being appreciated. :)

In case anybody wants to verify it: compile it before/after applying the
patch, with:
  make CFLAGS='-save-temps -DNDEBUG
and save x86_64-softmmu/cpu.s file from each run.

You are going to see some differences between both files due to __LINE__
being used as argument to object*_dynamic_cast_assert(), but nothing
else.

-- 
Eduardo