Re: [PATCH] mm/kasan: fix kasan_check_read() compiler warning

[Nick Desaulniers]

On Tue, Jul 9, 2019 at 11:36 AM Arnd Bergmann <arnd@xxxxxxxx> wrote:
>
> The kasan_check_read() is marked 'inline', which usually includes
> the 'always_inline' attribute. In some configuration, gcc decides that
> it cannot inline this, causing a build failure:
>
> In file included from include/linux/compiler.h:257,
>                  from arch/x86/include/asm/current.h:5,
>                  from include/linux/sched.h:12,
>                  from include/linux/ratelimit.h:6,
>                  from fs/dcache.c:18:
> include/linux/compiler.h: In function 'read_word_at_a_time':
> include/linux/kasan-checks.h:31:20: error: inlining failed in call to always_inline 'kasan_check_read': function attribute mismatch

Sounds like the error `function attribute mismatch` is saying:
kasan_check_read has one set of function attributes, but the call site
read_word_at_a_time has different function attributes, so I wont
inline kasan_check_read into read_word_at_a_time.
__no_kasan_or_inline changes based on CONFIG_KASAN; was this from a
kasan build or not?

>  static inline bool kasan_check_read(const volatile void *p, unsigned int size)
>                     ^~~~~~~~~~~~~~~~
> In file included from arch/x86/include/asm/current.h:5,
>                  from include/linux/sched.h:12,
>                  from include/linux/ratelimit.h:6,
>                  from fs/dcache.c:18:
> include/linux/compiler.h:280:2: note: called from here
>   kasan_check_read(addr, 1);
>   ^~~~~~~~~~~~~~~~~~~~~~~~~
>
> While I have no idea why it does this, but changing the call to the
> internal __kasan_check_read() fixes the issue.
>
> Fixes: dc55b51f312c ("mm/kasan: introduce __kasan_check_{read,write}")
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
>  include/linux/compiler.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index f0fd5636fddb..22909500ba1d 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -277,7 +277,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
>  static __no_kasan_or_inline
>  unsigned long read_word_at_a_time(const void *addr)
>  {
> -       kasan_check_read(addr, 1);
> +       __kasan_check_read(addr, 1);
>         return *(unsigned long *)addr;
>  }
>
> --
> 2.20.0
>


-- 
Thanks,
~Nick Desaulniers