Why didn't more x86 boxes break... well, it's pretty natural an
implementation of the BIOS to not clobber registers that aren't outputs.
Arguably the BIOSes that do are still buggy, since there isn't a
well-defined calling sequence for the BIOS and the convention that has
evolved is "don't clobber anything unless it's an output."
It's still wrong, however, especially since it means omitting the *real*
SMAP check.
-hpa
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