diff options
Diffstat (limited to 'openssl/doc/crypto/OPENSSL_ia32cap.pod')
-rw-r--r-- | openssl/doc/crypto/OPENSSL_ia32cap.pod | 113 |
1 files changed, 83 insertions, 30 deletions
diff --git a/openssl/doc/crypto/OPENSSL_ia32cap.pod b/openssl/doc/crypto/OPENSSL_ia32cap.pod index 2e659d34a..90156d219 100644 --- a/openssl/doc/crypto/OPENSSL_ia32cap.pod +++ b/openssl/doc/crypto/OPENSSL_ia32cap.pod @@ -2,42 +2,95 @@ =head1 NAME -OPENSSL_ia32cap - finding the IA-32 processor capabilities +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())) + unsigned int *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 -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. +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. 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 +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 |