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doc/crypto/OPENSSL_ia32cap.pod update [from HEAD].

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Andy Polyakov 2007-11-11 20:10:09 +00:00
parent 2ea3cd8abc
commit a1cc568288
1 changed files with 22 additions and 14 deletions
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doc/crypto/OPENSSL_ia32cap.pod
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@ -17,19 +17,27 @@ register after executing CPUID instruction with EAX=1 input value (see
Intel Application Note #241618). Naturally it's meaningful on IA-32[E] Intel Application Note #241618). Naturally it's meaningful on IA-32[E]
platforms only. The variable is normally set up automatically upon platforms only. The variable is normally set up automatically upon
toolkit initialization, but can be manipulated afterwards to modify toolkit initialization, but can be manipulated afterwards to modify
crypto library behaviour. For the moment of this writing three bits are crypto library behaviour. For the moment of this writing six bits are
significant, namely bit #28 denoting Hyperthreading, which is used to significant, namely:
distinguish Intel P4 core, bit #26 denoting SSE2 support, and bit #4
denoting presence of Time-Stamp Counter. Clearing bit #26 at run-time 1. bit #28 denoting Hyperthreading, which is used to distiguish
for example disables high-performance SSE2 code present in the crypto cores with shared cache;
library. You might have to do this if target OpenSSL application is 2. bit #26 denoting SSE2 support;
executed on SSE2 capable CPU, but under control of OS which does not 3. bit #25 denoting SSE support;
support SSE2 extentions. Even though you can manipulate the value 4. bit #23 denoting MMX support;
programmatically, you most likely will find it more appropriate to set 5. bit #20, reserved by Intel, is used to choose between RC4 code
up an environment variable with the same name prior starting target pathes;
application, e.g. 'env OPENSSL_ia32cap=0x10 apps/openssl', to achieve 6. bit #4 denoting presence of Time-Stamp Counter.
same effect without modifying the application source code.
Alternatively you can reconfigure the toolkit with no-sse2 option and For example, clearing bit #26 at run-time disables high-performance
recompile. 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 =cut