[PATCH] asm-generic: fix ffs -Wshadow warning

[PATCH] asm-generic: fix ffs -Wshadow warning

[Arnd Bergmann]

From: Arnd Bergmann <arnd@arndb.de>

gcc -Wshadow warns about the ffs() definition that has the
same name as the global ffs() built-in:

include/asm-generic/bitops/builtin-ffs.h:13:28: warning: declaration of 'ffs' shadows a built-in function [-Wshadow]

This is annoying because 'make W=2' warns every time this
header gets included.

Change it to use a #define instead, making callers directly
reference the builtin.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 include/asm-generic/bitops/builtin-ffs.h | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/include/asm-generic/bitops/builtin-ffs.h b/include/asm-generic/bitops/builtin-ffs.h
index 458c85ebcd15..1dacfdb4247e 100644
--- a/include/asm-generic/bitops/builtin-ffs.h
+++ b/include/asm-generic/bitops/builtin-ffs.h
@@ -10,9 +10,6 @@
  * the libc and compiler builtin ffs routines, therefore
  * differs in spirit from the above ffz (man ffs).
  */
-static __always_inline int ffs(int x)
-{
-	return __builtin_ffs(x);
-}
+#define ffs(x) __builtin_ffs(x)
 
 #endif
-- 
2.27.0

RE: [PATCH] asm-generic: fix ffs -Wshadow warning

[David Laight]

From: Arnd Bergmann
> Sent: 26 October 2020 16:00
> 
> From: Arnd Bergmann <arnd@arndb.de>
> 
> gcc -Wshadow warns about the ffs() definition that has the
> same name as the global ffs() built-in:
> 
> include/asm-generic/bitops/builtin-ffs.h:13:28: warning: declaration of 'ffs' shadows a built-in
> function [-Wshadow]
> 
> This is annoying because 'make W=2' warns every time this
> header gets included.
> 
> Change it to use a #define instead, making callers directly
> reference the builtin.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  include/asm-generic/bitops/builtin-ffs.h | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/include/asm-generic/bitops/builtin-ffs.h b/include/asm-generic/bitops/builtin-ffs.h
> index 458c85ebcd15..1dacfdb4247e 100644
> --- a/include/asm-generic/bitops/builtin-ffs.h
> +++ b/include/asm-generic/bitops/builtin-ffs.h
> @@ -10,9 +10,6 @@
>   * the libc and compiler builtin ffs routines, therefore
>   * differs in spirit from the above ffz (man ffs).
>   */
> -static __always_inline int ffs(int x)
> -{
> -	return __builtin_ffs(x);
> -}
> +#define ffs(x) __builtin_ffs(x)
> 
>  #endif
> --
> 2.27.0

An alternative would be to add #define ffs(x) our_inline_ffs(x)
before the inline function definition.

I though the idea of the __builtin_ prefix was that you could
have a function with the same name :-(

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH] asm-generic: fix ffs -Wshadow warning

[Arnd Bergmann]

On Mon, Oct 26, 2020 at 5:44 PM David Laight <David.Laight@aculab.com> wrote:
>
> An alternative would be to add #define ffs(x) our_inline_ffs(x)
> before the inline function definition.

Yes, that would also work.

> I though the idea of the __builtin_ prefix was that you could
> have a function with the same name :-(

It does multiple things, but one of the things it does is that
the ffs() falls back to the libc-provided ffs() function. You can
define a global ffs() like the libc implementation does, but
defining your own means that it will be used in place of
the official one, which is what the warning is for.

       Arnd