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Subject: Re: [PATCH] compiler.h: Fix barrier_data() on clang
To:     Andreas Schwab <schwab@linux-m68k.org>,
        Arvind Sankar <nivedita@alum.mit.edu>
Cc:     Nathan Chancellor <natechancellor@gmail.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        clang-built-linux@googlegroups.com, linux-kernel@vger.kernel.org,
        linux-riscv@lists.infradead.org
References: <20201014212631.207844-1-nivedita@alum.mit.edu>
 <87sg999ot0.fsf@igel.home>
From:   Randy Dunlap <rdunlap@infradead.org>
Message-ID: <0dbaca2d-9ad0-8c1a-a280-97be01cac2bd@infradead.org>
Date:   Mon, 16 Nov 2020 09:53:46 -0800
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On 11/16/20 9:47 AM, Andreas Schwab wrote:
> On Okt 14 2020, Arvind Sankar wrote:
> 
>> Commit
>>   815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
>>
>> neglected to copy barrier_data() from compiler-gcc.h into
>> compiler-clang.h. The definition in compiler-gcc.h was really to work
>> around clang's more aggressive optimization, so this broke
>> barrier_data() on clang, and consequently memzero_explicit() as well.
>>
>> For example, this results in at least the memzero_explicit() call in
>> lib/crypto/sha256.c:sha256_transform() being optimized away by clang.
>>
>> Fix this by moving the definition of barrier_data() into compiler.h.
>>
>> Also move the gcc/clang definition of barrier() into compiler.h,
>> __memory_barrier() is icc-specific (and barrier() is already defined
>> using it in compiler-intel.h) and doesn't belong in compiler.h.
>>
>> Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
>> Fixes: 815f0ddb346c ("include/linux/compiler*.h: make compiler-*.h mutually exclusive")
> 
> This breaks build on riscv:
> 
>   CC [M]  drivers/net/ethernet/emulex/benet/be_main.o
> In file included from ./include/vdso/processor.h:10,
>                  from ./arch/riscv/include/asm/processor.h:11,
>                  from ./include/linux/prefetch.h:15,
>                  from drivers/net/ethernet/emulex/benet/be_main.c:14:
> ./arch/riscv/include/asm/vdso/processor.h: In function 'cpu_relax':
> ./arch/riscv/include/asm/vdso/processor.h:14:2: error: implicit declaration of function 'barrier' [-Werror=implicit-function-declaration]
>    14 |  barrier();
>       |  ^~~~~~~
> cc1: some warnings being treated as errors
> make[5]: *** [scripts/Makefile.build:283: drivers/net/ethernet/emulex/benet/be_main.o] Error 1
> make[4]: *** [scripts/Makefile.build:500: drivers/net/ethernet/emulex/benet] Error 2
> make[3]: *** [scripts/Makefile.build:500: drivers/net/ethernet/emulex] Error 2
> make[2]: *** [scripts/Makefile.build:500: drivers/net/ethernet] Error 2
> make[1]: *** [scripts/Makefile.build:500: drivers/net] Error 2
> make: *** [Makefile:1799: drivers] Error 2

Hi,
What kernel version are you building?
This should be fixed in 5.10-rc4 by
commit 3347acc6fcd4ee71ad18a9ff9d9dac176b517329;
specifically this portion of it:

diff --git a/include/asm-generic/barrier.h b/include/asm-generic/barrier.h
index 798027bb89be..640f09479bdf 100644
--- a/include/asm-generic/barrier.h
+++ b/include/asm-generic/barrier.h
@@ -13,6 +13,7 @@
 
 #ifndef __ASSEMBLY__
 
+#include <linux/compiler.h>
 #include <asm/rwonce.h>
 
 #ifndef nop


-- 
~Randy