linux-kernel - Re: [PATCH] compiler.h: Fix barrier

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Message-ID: <87sg999ot0.fsf@igel.home>
Date:   Mon, 16 Nov 2020 18:47:23 +0100
From:   Andreas Schwab <schwab@...ux-m68k.org>
To:     Arvind Sankar <nivedita@...m.mit.edu>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org
Subject: Re: [PATCH] compiler.h: Fix barrier_data() on clang

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@...m.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

Andreas.

-- 
Andreas Schwab, schwab@...ux-m68k.org
GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510  2552 DF73 E780 A9DA AEC1
"And now for something completely different."