Re: [PATCH] compiler.h: Fix barrier_data() on clang

Randy Dunlap
2020-11-16T17:54:14Z

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