Lack of documentation for OPENSSL_ia32cap_P

Jan Just Keijser janjust at
Sat Jul 25 23:56:10 UTC 2020

On 23/07/20 02:35, Jakob Bohm via openssl-users wrote:
> The OPENSSL_ia32cap_P variable, its bitfields and the code that sets
> it (in assembler) seemto have no clear documentation.
> Looking at, I see jumps to ".Lintel" etc. being 
> conditional
> on stuff other than the CPU being an Intel CPU, while the code in 
> there is
> generally unreadable due to the backwards SCO assembler format and the 
> lack
> of clear comments about register usage such as "Here, EDX holds XXX 
> and ESI
> holds YYYY" or eventhe code rationale "P50 microarchitecture stepping A
> incorrectly implements FDIV, so clear out private bit for using that in
> bignum implementations"
> As there is an external interface for changing the variable via an 
> environment
> var, the lack of documentation makes that useless except for "cargo-cult"
> copying of values from old mailing list posts.
in the openssl 1.1.1g tree there's a file 'doc/man3/OPENSSL_ia32cap.pod' 
which documents it a little - not sure if that is still up-to-date though...



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