diff options
Diffstat (limited to 'doc/crypto/OPENSSL_ia32cap.pod')
-rw-r--r-- | doc/crypto/OPENSSL_ia32cap.pod | 96 |
1 files changed, 0 insertions, 96 deletions
diff --git a/doc/crypto/OPENSSL_ia32cap.pod b/doc/crypto/OPENSSL_ia32cap.pod deleted file mode 100644 index 5bcb82e3cfed..000000000000 --- a/doc/crypto/OPENSSL_ia32cap.pod +++ /dev/null @@ -1,96 +0,0 @@ -=pod - -=head1 NAME - -OPENSSL_ia32cap, OPENSSL_ia32cap_loc - the IA-32 processor capabilities vector - -=head1 SYNOPSIS - - unsigned long *OPENSSL_ia32cap_loc(void); - #define OPENSSL_ia32cap ((OPENSSL_ia32cap_loc())[0]) - -=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:ECX register pair after executing CPUID instruction with EAX=1 -input value (see Intel Application Note #241618). Naturally it's -meaningful on x86 and x86_64 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 following bits are significant: - -=over - -=item bit #4 denoting presence of Time-Stamp Counter. - -=item bit #19 denoting availability of CLFLUSH instruction; - -=item bit #20, reserved by Intel, is used to choose among RC4 code paths; - -=item bit #23 denoting MMX support; - -=item bit #24, FXSR bit, denoting availability of XMM registers; - -=item bit #25 denoting SSE support; - -=item bit #26 denoting SSE2 support; - -=item bit #28 denoting Hyperthreading, which is used to distinguish -cores with shared cache; - -=item bit #30, reserved by Intel, denotes specifically Intel CPUs; - -=item bit #33 denoting availability of PCLMULQDQ instruction; - -=item bit #41 denoting SSSE3, Supplemental SSE3, support; - -=item bit #43 denoting AMD XOP support (forced to zero on non-AMD CPUs); - -=item bit #57 denoting AES-NI instruction set extension; - -=item bit #59, OSXSAVE bit, denoting availability of YMM registers; - -=item bit #60 denoting AVX extension; - -=item bit #62 denoting availability of RDRAND instruction; - -=back - -For example, clearing bit #26 at run-time disables high-performance -SSE2 code present in the crypto library, while clearing bit #24 -disables SSE2 code operating on 128-bit XMM register bank. You might -have to do the latter if target OpenSSL application is executed on SSE2 -capable CPU, but under control of OS that does not enable XMM -registers. 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=0x16980010 apps/openssl', or -better yet 'env OPENSSL_ia32cap=~0x1000000 apps/openssl' to achieve same -effect without modifying the application source code. Alternatively you -can reconfigure the toolkit with no-sse2 option and recompile. - -Less intuitive is clearing bit #28. The truth is that it's not copied -from CPUID output verbatim, but is adjusted to reflect whether or not -the data cache is actually shared between logical cores. This in turn -affects the decision on whether or not expensive countermeasures -against cache-timing attacks are applied, most notably in AES assembler -module. - -The vector is further extended with EBX value returned by CPUID with -EAX=7 and ECX=0 as input. Following bits are significant: - -=over - -=item bit #64+3 denoting availability of BMI1 instructions, e.g. ANDN; - -=item bit #64+5 denoting availability of AVX2 instructions; - -=item bit #64+8 denoting availability of BMI2 instructions, e.g. MUXL -and RORX; - -=item bit #64+18 denoting availability of RDSEED instruction; - -=item bit #64+19 denoting availability of ADCX and ADOX instructions; - -=back |