Add framework for yet another assembler module dubbed "cpuid." Idea

is to have a placeholder to small routines, which can be written only
in assembler. In IA-32 case this includes processor capability
identification and access to Time-Stamp Counter. As discussed earlier
OPENSSL_ia32cap is introduced to control recently added SSE2 code
pathes (see docs/crypto/OPENSSL_ia32cap.pod). For the moment the
code is operational on ELF platforms only. I haven't checked it yet,
but I have all reasons to believe that Windows build should fail to
link too. I'll be looking into it shortly...

1 files changed, 34 insertions, 0 deletions

diff --git a/doc/crypto/OPENSSL_ia32cap.pod b/doc/crypto/OPENSSL_ia32cap.pod
new file mode 100644
index 0000000000..46afd19880
--- /dev/null
+++ b/doc/crypto/OPENSSL_ia32cap.pod
@@ -0,0 +1,34 @@
+=pod
+
+=head1 NAME
+
+OPENSSL_ia32cap
+
+=head1 SYNOPSIS
+
+ extern unsigned long OPENSSL_ia32cap;
+ unsigned long *OPENSSL_ia32cap_loc();
+
+=head1 DESCRIPTION
+
+OPENSSL_ia32cap is 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 defined/meaningful on IA-32 platforms only.
+The variable is normally set up automatically upon toolkit
+initialization and can be manipulated afterwards to modify crypto
+library behaviour. For the moment of this writing only two bits are
+significant, namely bit #26 denoting SSE2 support, and bit #4 denoting
+presence of Time-Stamp Counter. Resetting 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 programmatically
+manipulate the value, 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=0x10 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