43 lines
1.7 KiB
Text
43 lines
1.7 KiB
Text
=pod
|
|
|
|
=head1 NAME
|
|
|
|
OPENSSL_ia32cap - finding the IA-32 processor capabilities
|
|
|
|
=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 six bits are
|
|
significant, namely:
|
|
|
|
1. bit #28 denoting Hyperthreading, which is used to distiguish
|
|
cores with shared cache;
|
|
2. bit #26 denoting SSE2 support;
|
|
3. bit #25 denoting SSE support;
|
|
4. bit #23 denoting MMX support;
|
|
5. bit #20, reserved by Intel, is used to choose between RC4 code
|
|
pathes;
|
|
6. bit #4 denoting presence of Time-Stamp Counter.
|
|
|
|
For example, clearing bit #26 at run-time 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. on Intel P4 processor 'env
|
|
OPENSSL_ia32cap=0x12900010 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
|