Add OPENSSL_SMALL.

Intel's P-256 code has very large tables and things like Chromium just
don't need that extra size. However, servers generally do so this change
adds an OPENSSL_SMALL define that currently just drops the 64-bit P-224
but will gate Intel's P-256 in the future too.

Change-Id: I2e55c6e06327fafabef9b96d875069d95c0eea81
Reviewed-on: https://boringssl-review.googlesource.com/6362
Reviewed-by: Adam Langley <alangley@gmail.com>

BUILDING.md

@@ -71,6 +71,10 @@ Windows, where functions need to be tagged with `dllimport` when coming from a
 shared library, define `BORINGSSL_SHARED_LIBRARY` in any code which `#include`s
 the BoringSSL headers.
 
+In order to serve environments where code-size is important as well as those
+where performance is the overriding concern, `OPENSSL_SMALL` can be defined to
+remove some code that is especially large.
+
 ### Building for Android
 
 It's possible to build BoringSSL with the Android NDK using CMake. This has

CMakeLists.txt

@@ -81,6 +81,7 @@ if((CMAKE_COMPILER_IS_GNUCXX AND CMAKE_C_COMPILER_VERSION VERSION_GREATER "4.8.9
 endif()
 
 add_definitions(-DBORINGSSL_IMPLEMENTATION)
+add_definitions(-DOPENSSL_SMALL)
 
 if (BUILD_SHARED_LIBS)
   add_definitions(-DBORINGSSL_SHARED_LIBRARY)

crypto/ec/ec.c

@@ -228,7 +228,7 @@ static const struct curve_data P521 = {
 const struct built_in_curve OPENSSL_built_in_curves[] = {
     {
         NID_secp224r1, &P224,
-#if defined(BORINGSSL_USE_INT128_CODE)
+#if defined(BORINGSSL_USE_INT128_CODE) && !defined(OPENSSL_SMALL)
         EC_GFp_nistp224_method,
 #else
         0,

crypto/ec/p224-64.c

@@ -19,7 +19,8 @@
 
 #include <openssl/base.h>
 
-#if defined(OPENSSL_64_BIT) && !defined(OPENSSL_WINDOWS)
+#if defined(OPENSSL_64_BIT) && !defined(OPENSSL_WINDOWS) && \
+    !defined(OPENSSL_SMALL)
 
 #include <openssl/bn.h>
 #include <openssl/ec.h>
@@ -1337,4 +1338,4 @@ const EC_METHOD *EC_GFp_nistp224_method(void) {
   return &ret;
 }
 
-#endif
+#endif  /* 64_BIT && !WINDOWS && !SMALL */