Switch __ARM_FEATURE_CRYPTO to __ARM_FEATURE_{AES,SHA2}.
The latest version of ACLE splits __ARM_FEATURE_CRYPTO into two defines
to reflect that, starting ARMv8.2, the cryptography extension can
include {AES,PMULL} and {SHA1,SHA256} separately.
Also standardize on __ARM_NEON, which is the recommended symbol from
ACLE, and the only one defined on non-Apple aarch64 targets. Digging
through GCC history, __ARM_NEON__ is a bit older. __ARM_NEON was added
in GCC's 9e94a7fc5ab770928b9e6a2b74e292d35b4c94da from 2012, part of GCC
4.8.0.
I suspect we can stop paying attention to __ARM_NEON__ at this point,
but I've left both working for now. __ARM_FEATURE_{AES,SHA2} is definite
too new to fully replace __ARM_FEATURE_CRYPTO.
Tested on Linux that -march=armv8-a+aes now also drops the fallback AES
code. Previously, we would pick up -march=armv8-a+crypto, but not
-march=armv8-a+aes. Also tested that, on an OPENSSL_STATIC_ARMCAP build,
-march=armv8-a+sha2 sets the SHA-1 and SHA-256 features.
Change-Id: I749bdbc501ba2da23177ddb823547efcd77e5c98
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/50847
Reviewed-by: Adam Langley <agl@google.com>
diff --git a/BUILDING.md b/BUILDING.md
index 64b1520..10645be 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -170,10 +170,12 @@
capability information has to be provided by a combination of compile-time
information and the operating system.
-BoringSSL determines capabilities at compile-time based on `__ARM_NEON__`,
-`__ARM_FEATURE_CRYPTO`, and other preprocessor symbols reported by the compiler.
+BoringSSL determines capabilities at compile-time based on `__ARM_NEON`,
+`__ARM_FEATURE_AES`, and other preprocessor symbols defined in
+[Arm C Language Extensions (ACLE)](https://developer.arm.com/architectures/system-architectures/software-standards/acle).
These values are usually controlled by the `-march` flag. You can also define
-any of the following to enable the corresponding ARM feature.
+any of the following to enable the corresponding ARM feature, but using the ACLE
+symbols via `-march` is recommended.
* `OPENSSL_STATIC_ARMCAP_NEON`
* `OPENSSL_STATIC_ARMCAP_AES`
