[PATCH] mips: Fix unroll macro when building with Clang

From: Nathan Chancellor <natechancellor@gmail.com>
To: Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <paul.burton@mips.com>,
	James Hogan <jhogan@kernel.org>
Cc: linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org,
	clang-built-linux@googlegroups.com,
	Nick Desaulniers <ndesaulniers@google.com>,
	Nathan Chancellor <natechancellor@gmail.com>
Subject: [PATCH] mips: Fix unroll macro when building with Clang
Date: Thu, 10 Oct 2019 13:31:59 -0700	[thread overview]
Message-ID: <20191010203159.20565-1-natechancellor@gmail.com> (raw)

Building with Clang errors after commit 6baaeadae911 ("MIPS: Provide
unroll() macro, use it for cache ops") since the GCC_VERSION macro
is defined in include/linux/compiler-gcc.h, which is only included
in compiler.h when using GCC:

In file included from arch/mips/kernel/mips-mt.c:20:
./arch/mips/include/asm/r4kcache.h:254:1: error: use of undeclared
identifier 'GCC_VERSION'; did you mean 'S_VERSION'?
__BUILD_BLAST_CACHE(i, icache, Index_Invalidate_I, Hit_Invalidate_I, 32,
)
^
./arch/mips/include/asm/r4kcache.h:219:4: note: expanded from macro
'__BUILD_BLAST_CACHE'
                        cache_unroll(32, kernel_cache, indexop,
                        ^
./arch/mips/include/asm/r4kcache.h:203:2: note: expanded from macro
'cache_unroll'
        unroll(times, _cache_op, insn, op, (addr) + (i++ * (lsize)));
        ^
./arch/mips/include/asm/unroll.h:28:15: note: expanded from macro
'unroll'
        BUILD_BUG_ON(GCC_VERSION >= 40700 &&                    \
                     ^

Use CONFIG_GCC_VERSION, which will always be set by Kconfig.
Additionally, Clang 8 had improvements around __builtin_constant_p so
use that as a lower limit for this check with Clang (although MIPS
wasn't buildable until Clang 9); building a kernel with Clang 9.0.0
has no issues after this change.

Fixes: 6baaeadae911 ("MIPS: Provide unroll() macro, use it for cache ops")
Link: https://github.com/ClangBuiltLinux/linux/issues/736
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
 arch/mips/include/asm/unroll.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/mips/include/asm/unroll.h b/arch/mips/include/asm/unroll.h
index df1cdcfc5a47..c628747d4ecd 100644
--- a/arch/mips/include/asm/unroll.h
+++ b/arch/mips/include/asm/unroll.h
@@ -25,7 +25,8 @@
 	 * generate reasonable code for the switch statement,	\
 	 * so we skip the sanity check for those compilers.	\
 	 */							\
-	BUILD_BUG_ON(GCC_VERSION >= 40700 &&			\
+	BUILD_BUG_ON((CONFIG_GCC_VERSION >= 40700 ||		\
+		      CONFIG_CLANG_VERSION >= 80000) &&		\
 		     !__builtin_constant_p(times));		\
 								\
 	switch (times) {					\
-- 
2.23.0

