* Paul E. McKenney [off-list ref] wrote:

From: Will Deacon <redacted>

linux/compiler.h is included indirectly by linux/types.h via
uapi/linux/types.h -> uapi/linux/posix_types.h -> linux/stddef.h
-> uapi/linux/stddef.h and is needed to provide a proper definition of
offsetof.

Unfortunately, compiler.h requires a definition of
smp_read_barrier_depends() for defining lockless_dereference and soon
for defining READ_ONCE, which means that all
users of READ_ONCE will need to include asm/barrier.h to avoid splats
such as:

   In file included from include/uapi/linux/stddef.h:1:0,
                    from include/linux/stddef.h:4,
                    from arch/h8300/kernel/asm-offsets.c:11:
   include/linux/list.h: In function 'list_empty':

quoted

quoted

include/linux/compiler.h:343:2: error: implicit declaration of function 'smp_read_barrier_depends' [-Werror=implicit-function-declaration]

     smp_read_barrier_depends(); /* Enforce dependency ordering from x */ \
     ^

A better alternative is to include asm/barrier.h in linux/compiler.h,
but this requires a type definition for "bool" on some architectures
(e.g. x86), which is defined later by linux/types.h. Type "bool" is also
used directly in linux/compiler.h, so the whole thing is pretty fragile.

This patch splits compiler.h in two: compiler-types.h contains type
annotations, definitions and the compiler-specific parts, whereas
compiler.h #includes compiler-types.h and additionally defines macros
such as {READ,WRITE.ACCESS}_ONCE.

uapi/linux/stddef.h and linux/linkage.h are then moved over to include
linux/compiler-types.h, which fixes the build for h8 and blackfin.

Reported-by: kbuild test robot <redacted>
Signed-off-by: Will Deacon <redacted>
Signed-off-by: Paul E. McKenney <redacted>
[ paulmck: Add Will's fixes for issues reported by kbuild test robot. ]
---
 arch/arm/include/asm/ptrace.h   |   3 +-
 arch/sparc/include/asm/ptrace.h |   1 +
 arch/um/include/shared/init.h   |   2 +-
 include/linux/compiler-clang.h  |   2 +-
 include/linux/compiler-gcc.h    |   2 +-
 include/linux/compiler-intel.h  |   2 +-
 include/linux/compiler-types.h  | 274 ++++++++++++++++++++++++++++++++++++++++
 include/linux/compiler.h        | 265 +-------------------------------------

The common pattern is to use an underscore (compiler_types.h), not a hyphen 
(compiler-types.h) ...

Even the patch description cites such an example, posix_types.h:

linux/compiler.h is included indirectly by linux/types.h via
uapi/linux/types.h -> uapi/linux/posix_types.h -> linux/stddef.h

Thanks,

	Ingo