linux-kernel - [PATCH AUTOSEL 4.4 18/37] lib/mpi: Fix 64-bit MIPS build with Clang

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Message-Id: <20200608232750.3370747-18-sashal@kernel.org>
Date:   Mon,  8 Jun 2020 19:27:30 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Sasha Levin <sashal@...nel.org>,
        clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 4.4 18/37] lib/mpi: Fix 64-bit MIPS build with Clang

From: Nathan Chancellor <natechancellor@...il.com>

[ Upstream commit 18f1ca46858eac22437819937ae44aa9a8f9f2fa ]

When building 64r6_defconfig with CONFIG_MIPS32_O32 disabled and
CONFIG_CRYPTO_RSA enabled:

lib/mpi/generic_mpih-mul1.c:37:24: error: invalid use of a cast in a
inline asm context requiring an l-value: remove the cast
or build with -fheinous-gnu-extensions
                umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
                ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lib/mpi/longlong.h:664:22: note: expanded from macro 'umul_ppmm'
                 : "=d" ((UDItype)(w0))
                         ~~~~~~~~~~^~~
lib/mpi/generic_mpih-mul1.c:37:13: error: invalid use of a cast in a
inline asm context requiring an l-value: remove the cast
or build with -fheinous-gnu-extensions
                umul_ppmm(prod_high, prod_low, s1_ptr[j], s2_limb);
                ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
lib/mpi/longlong.h:668:22: note: expanded from macro 'umul_ppmm'
                 : "=d" ((UDItype)(w1))
                         ~~~~~~~~~~^~~
2 errors generated.

This special case for umul_ppmm for MIPS64r6 was added in
commit bbc25bee37d2b ("lib/mpi: Fix umul_ppmm() for MIPS64r6"), due to
GCC being inefficient and emitting a __multi3 intrinsic.

There is no such issue with clang; with this patch applied, I can build
this configuration without any problems and there are no link errors
like mentioned in the commit above (which I can still reproduce with
GCC 9.3.0 when that commit is reverted). Only use this definition when
GCC is being used.

This really should have been caught by commit b0c091ae04f67 ("lib/mpi:
Eliminate unused umul_ppmm definitions for MIPS") when I was messing
around in this area but I was not testing 64-bit MIPS at the time.

Link: https://github.com/ClangBuiltLinux/linux/issues/885
Reported-by: Dmitry Golovin <dima@...ovin.in>
Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 lib/mpi/longlong.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/mpi/longlong.h b/lib/mpi/longlong.h
index f1f31c754b3e..70f5cf8deab3 100644
--- a/lib/mpi/longlong.h
+++ b/lib/mpi/longlong.h
@@ -671,7 +671,7 @@ do {						\
 	**************  MIPS/64  **************
 	***************************************/
 #if (defined(__mips) && __mips >= 3) && W_TYPE_SIZE == 64
-#if defined(__mips_isa_rev) && __mips_isa_rev >= 6
+#if defined(__mips_isa_rev) && __mips_isa_rev >= 6 && defined(CONFIG_CC_IS_GCC)
 /*
  * GCC ends up emitting a __multi3 intrinsic call for MIPS64r6 with the plain C
  * code below, so we special case MIPS64r6 until the compiler can do better.
-- 
2.25.1