1=pod 2 3=head1 NAME 4 5OPENSSL_ia32cap - finding the IA-32 processor capabilities 6 7=head1 SYNOPSIS 8 9 unsigned long *OPENSSL_ia32cap_loc(void); 10 #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc())) 11 12=head1 DESCRIPTION 13 14Value returned by OPENSSL_ia32cap_loc() is address of a variable 15containing IA-32 processor capabilities bit vector as it appears in EDX 16register after executing CPUID instruction with EAX=1 input value (see 17Intel Application Note #241618). Naturally it's meaningful on IA-32[E] 18platforms only. The variable is normally set up automatically upon 19toolkit initialization, but can be manipulated afterwards to modify 20crypto library behaviour. For the moment of this writing three bits are 21significant, namely bit #28 denoting Hyperthreading, which is used to 22distinguish Intel P4 core, bit #26 denoting SSE2 support, and bit #4 23denoting presence of Time-Stamp Counter. Clearing bit #26 at run-time 24for example disables high-performance SSE2 code present in the crypto 25library. You might have to do this if target OpenSSL application is 26executed on SSE2 capable CPU, but under control of OS which does not 27support SSE2 extentions. Even though you can manipulate the value 28programmatically, you most likely will find it more appropriate to set 29up an environment variable with the same name prior starting target 30application, e.g. 'env OPENSSL_ia32cap=0x10 apps/openssl', to achieve 31same effect without modifying the application source code. 32Alternatively you can reconfigure the toolkit with no-sse2 option and 33recompile. 34 35=cut 36