Re: [PATCH] Handle SForced in storage_modifiers

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

On Mon, Nov 14, 2016 at 02:12:16PM -0500, Jeff Layton wrote:
> We have been seeing errors like this for a while now in the sparse
> Fedora package, when doing kernel builds:
> 
>     ./include/linux/err.h:53:25: warning: dereference of noderef expression
>     ./include/linux/err.h:35:16: warning: dereference of noderef expression
> 
> This spews all over the build because this comes from IS_ERR(), which
> is called everywhere. Even odder, it turns out that if we build the
> package with -fpic turned off, then it works fine.
> 
> With some brute-force debugging, I think I've finally found the cause.
> This array is missing the SForced element. When this is added then the
> problem goes away.
> 
> As to why this goes away when -fpic is removed, I can only assume that
> we get lucky with the memory layout and have a zeroed out region just
> beyond the end of the array.
> 
> Fixes: 3829c4d8b097776e6b3472290a9fae08a705ab7a
> Cc: Al Viro <viro@ftp.linux.org.uk>
> Signed-off-by: Jeff Layton <jlayton@redhat.com>
> ---
>  parse.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/parse.c b/parse.c
> index 205e12644a6c..b290ff2636f2 100644
> --- a/parse.c
> +++ b/parse.c
> @@ -1286,7 +1286,8 @@ static unsigned long storage_modifiers(struct decl_state *ctx)
>  		[SAuto] = MOD_AUTO,
>  		[SExtern] = MOD_EXTERN,
>  		[SStatic] = MOD_STATIC,
> -		[SRegister] = MOD_REGISTER
> +		[SRegister] = MOD_REGISTER,
> +		[SForced] = 0
>  	};
>  	return mod[ctx->storage_class] | (ctx->is_inline ? MOD_INLINE : 0)
>  		| (ctx->is_tls ? MOD_TLS : 0);
> -- 

Humm,

The array is statically initialized and never modified,
your patch shouldn't change anything, and this regardless of
the memory layout or compiler options.


Luc Van Oostenryck