Re: [PATCH 2/2] compiler.h: Include asm/rwonce.h under ARM64 and ALPHA to fix build errors

[Yonghong Song]

On 1/13/21 2:57 AM, Tiezhu Yang wrote:
> When make M=samples/bpf on the Loongson 3A3000 platform which
> belongs to MIPS arch, there exists many similar build errors
> about 'asm/rwonce.h' file not found, so include it only under
> CONFIG_ARM64 and CONFIG_ALPHA due to it exists only in arm64
> and alpha arch.
>
>    CLANG-bpf  samples/bpf/xdpsock_kern.o
> In file included from samples/bpf/xdpsock_kern.c:2:
> In file included from ./include/linux/bpf.h:9:
> In file included from ./include/linux/workqueue.h:9:
> In file included from ./include/linux/timer.h:5:
> In file included from ./include/linux/list.h:9:
> In file included from ./include/linux/kernel.h:10:
> ./include/linux/compiler.h:246:10: fatal error: 'asm/rwonce.h' file not found
>           ^~~~~~~~~~~~~~
> 1 error generated.
>
> $ find . -name rwonce.h
> ./include/asm-generic/rwonce.h
> ./arch/arm64/include/asm/rwonce.h
> ./arch/alpha/include/asm/rwonce.h
>
> Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> ---
>   include/linux/compiler.h | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index b8fe0c2..bdbe759 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -243,6 +243,12 @@ static inline void *offset_to_ptr(const int *off)
>    */
>   #define prevent_tail_call_optimization()	mb()
>   
> +#ifdef CONFIG_ARM64
>   #include <asm/rwonce.h>
> +#endif
> +
> +#ifdef CONFIG_ALPHA
> +#include <asm/rwonce.h>
> +#endif

I do not think this fix is correct. x86 does not define its own
rwonce.h and still compiles fine.

As noted in the above, we have include/asm-generic/rwonce.h.
Once you do a proper build, you will have rwonce.h in arch
generated directory like

-bash-4.4$ find . -name rwonce.h
./include/asm-generic/rwonce.h
./arch/alpha/include/asm/rwonce.h
./arch/arm64/include/asm/rwonce.h
./arch/x86/include/generated/asm/rwonce.h

for mips, it should generated in 
arch/mips/include/generated/asm/rwonce.h. Please double check why this 
does not happen.

>   
>   #endif /* __LINUX_COMPILER_H */