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