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Diffstat (limited to 'doc/crypto/OPENSSL_ia32cap.pod')
-rw-r--r-- | doc/crypto/OPENSSL_ia32cap.pod | 34 |
1 files changed, 34 insertions, 0 deletions
diff --git a/doc/crypto/OPENSSL_ia32cap.pod b/doc/crypto/OPENSSL_ia32cap.pod new file mode 100644 index 0000000000..46afd19880 --- /dev/null +++ b/doc/crypto/OPENSSL_ia32cap.pod @@ -0,0 +1,34 @@ +=pod + +=head1 NAME + +OPENSSL_ia32cap + +=head1 SYNOPSIS + + extern unsigned long OPENSSL_ia32cap; + unsigned long *OPENSSL_ia32cap_loc(); + +=head1 DESCRIPTION + +OPENSSL_ia32cap is a variable containing IA-32 processor capabilities +bit vector as it appears in EDX register after executing CPUID +instruction with EAX=1 input value (see Intel Application Note +#241618). Naturally it's defined/meaningful on IA-32 platforms only. +The variable is normally set up automatically upon toolkit +initialization and can be manipulated afterwards to modify crypto +library behaviour. For the moment of this writing only two bits are +significant, namely bit #26 denoting SSE2 support, and bit #4 denoting +presence of Time-Stamp Counter. Resetting bit #26 at run-time for +example disables high-performance SSE2 code present in the crypto +library. You might have to do this if target OpenSSL application is +executed on SSE2 capable CPU, but under control of OS which does not +support SSE2 extentions. Even though you can programmatically +manipulate the value, you most likely will find it more appropriate to +set up an environment variable with the same name prior starting target +application, e.g. 'env OPENSSL_ia32cap=0x10 apps/openssl', to achieve +same effect without modifying the application source code. +Alternatively you can reconfigure the toolkit with no-sse2 option and +recompile. + +=cut |