&xor ("ecx","eax");
&bt ("ecx",21);
&jnc (&label("nocpuid"));
+ &xor ("eax","eax");
+ &cpuid ();
+ &xor ("eax","eax");
+ &cmp ("ebx",0x756e6547); # "Genu"
+ &setne (&LB("eax"));
+ &mov ("ebp","eax");
+ &cmp ("edx",0x49656e69); # "ineI"
+ &setne (&LB("eax"));
+ &or ("ebp","eax");
+ &cmp ("ecx",0x6c65746e); # "ntel"
+ &setne (&LB("eax"));
+ &or ("ebp","eax");
&mov ("eax",1);
&cpuid ();
+ &bt ("edx",28); # test hyper-threading bit
+ &jnc (&label("nocpuid"));
+ &cmp ("ebp",0);
+ &jne (&label("notintel"));
+ &or ("edx",1<<20); # use reserved bit to engage RC4_CHAR
+&set_label("notintel");
+ &shr ("ebx",16);
+ &cmp (&LB("ebx"),1); # see if cache is shared(*)
+ &ja (&label("nocpuid"));
+ &and ("edx",~(1<<28)); # clear hyper-threading bit if not
&set_label("nocpuid");
&mov ("eax","edx");
&mov ("edx","ecx");
&function_end("OPENSSL_ia32_cpuid");
+# (*) on Core2 this value is set to 2 denoting the fact that L2
+# cache is shared between cores.
&external_label("OPENSSL_ia32cap_P");
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 five bits are
-significant, namely bit #28 denoting Hyperthreading, which is used to
-distinguish Intel P4 core, bit #26 denoting SSE2 support, bit #25
-denoting SSE support, bit #23 denoting MMX support, and bit #4 denoting
-presence of Time-Stamp Counter. Clearing bit #26 at run-time for
-example 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. 'env OPENSSL_ia32cap=0x12800010 apps/openssl', to
-achieve same effect without modifying the application source code.
-Alternatively you can reconfigure the toolkit with no-sse2 option and
-recompile.
+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