Re: [PATCH 16/19] linux/compiler.h: Split into compiler.h and compiler-types.h

[Ingo Molnar]

* Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> wrote:

> From: Will Deacon <will.deacon@xxxxxxx>
> 
> 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':
> >> 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 <fengguang.wu@xxxxxxxxx>
> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> [ 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