| =pod |
| |
| =head1 NAME |
| |
| OPENSSL_ia32cap |
| |
| =head1 SYNOPSIS |
| |
| unsigned long *OPENSSL_ia32cap_loc(void); |
| #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc())) |
| |
| =head1 DESCRIPTION |
| |
| Value returned by OPENSSL_ia32cap_loc() is address of 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 meaningful on IA-32[E] |
| platforms only. The variable is normally set up automatically upon |
| toolkit initialization, but can be manipulated afterwards to modify |
| crypto library behaviour. For the moment of this writing three bits are |
| significant, namely bit #28 denoting Hyperthreading, which is used to |
| distinguish Intel P4 core, bit #26 denoting SSE2 support, and bit #4 |
| denoting presence of Time-Stamp Counter. Clearing 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 manipulate the value |
| programmatically, 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 |
