x86_64-mont5.pl checks for both BMI1 and BMI2, because the MULX path
also uses the ANDN instruction. Some history here from upstream:
a5bb5bca52f57021a4017521c55a6b3590bbba7a, dated 2013-10-03, added the
MULX path to x86_64-mont5.pl. At the time, the cpuid check was
BMI2+ADX. (MULX comes from BMI2.)
37de2b5c1e370b493932552556940eb89922b027, dated 2013-10-09, made
BN_mod_exp_mont_consttime prefer the MULX mont5 code over the AVX2 rsaz
code, with a matching BMI2+ADX cpuid check.
8fc8f486f7fa098c9fbb6a6ae399e3c6856e0d87, dated 2016-01-25, tweaked some
code to use the ANDN instruction, from BMI1. Correspondingly, it changed
the cpuid check to be BMI1+BMI2+ADX. The BN_mod_exp_mont_consttime check
was left unchanged.
This CL fixes our version of the BN_mod_exp_mont_consttime check to
match the assembly, by also checking BMI1. (This should be a no-op.
Presumably any processor with BMI2 also has BMI1.)
Change-Id: Ib0cacc7e2be840d970460eef4dd9ded7fb24231c
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/51547
Reviewed-by: Adam Langley <agl@google.com>
David Benjamin
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