Allow .arch directives with Clang.
Some, very recent, versions of Clang now support `.arch`. Allow them to
see these directives with BORINGSSL_CLANG_SUPPORTS_DOT_ARCH.
BUG=39
Change-Id: I122ab4b3d5f14502ffe0c6e006950dc64abf0201
Reviewed-on: https://boringssl-review.googlesource.com/10600
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: Adam Langley <agl@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>
diff --git a/BUILDING.md b/BUILDING.md
index 5631ded..522bee1 100644
--- a/BUILDING.md
+++ b/BUILDING.md
@@ -134,6 +134,18 @@
Note that if a feature is enabled in this way, but not actually supported at
run-time, BoringSSL will likely crash.
+## Assembling ARMv8 with Clang
+
+In order to support the ARMv8 crypto instructions, Clang requires that the
+architecture be `armv8-a+crypto`. However, setting that as a general build flag
+would allow the compiler to assume that crypto instructions are *always*
+supported, even without testing for them.
+
+It's possible to set the architecture in an assembly file using the `.arch`
+directive, but only very recent versions of Clang support this. If
+`BORINGSSL_CLANG_SUPPORTS_DOT_ARCH` is defined then `.arch` directives will be
+used with Clang, otherwise you may need to craft acceptable assembler flags.
+
# Running tests
There are two sets of tests: the C/C++ tests and the blackbox tests. For former
diff --git a/crypto/aes/asm/aesv8-armx.pl b/crypto/aes/asm/aesv8-armx.pl
index 121154a..a180426 100644
--- a/crypto/aes/asm/aesv8-armx.pl
+++ b/crypto/aes/asm/aesv8-armx.pl
@@ -51,7 +51,7 @@
.text
___
$code.=<<___ if ($flavour =~ /64/);
-#if !defined(__clang__)
+#if !defined(__clang__) || defined(BORINGSSL_CLANG_SUPPORTS_DOT_ARCH)
.arch armv8-a+crypto
#endif
___
diff --git a/crypto/modes/asm/ghashv8-armx.pl b/crypto/modes/asm/ghashv8-armx.pl
index 3a7b8d8..15fc478 100644
--- a/crypto/modes/asm/ghashv8-armx.pl
+++ b/crypto/modes/asm/ghashv8-armx.pl
@@ -59,7 +59,7 @@
.text
___
$code.=<<___ if ($flavour =~ /64/);
-#if !defined(__clang__)
+#if !defined(__clang__) || defined(BORINGSSL_CLANG_SUPPORTS_DOT_ARCH)
.arch armv8-a+crypto
#endif
___
