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Date: Fri, 9 Sep 2005 18:34:15 +0100
From: viro@ZenIV.linux.org.uk
To: Linus Torvalds <torvalds@osdl.org>
Cc: Andreas Schwab <schwab@suse.de>, linux-kernel@vger.kernel.org
Subject: Re: [sparse fix] (was Re: [PATCH] bogus cast in bio.c)
Message-ID: <20050909173415.GS9623@ZenIV.linux.org.uk>
References: <20050909155356.GF9623@ZenIV.linux.org.uk> <je4q8u1agp.fsf@sykes.suse.de> <20050909163643.GO9623@ZenIV.linux.org.uk> <20050909172938.GQ9623@ZenIV.linux.org.uk>
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On Fri, Sep 09, 2005 at 06:29:38PM +0100, viro@ZenIV.linux.org.uk wrote:
> > fs/bio.c:686:15: warning: incorrect type in assignment (different address spaces)
> > fs/bio.c:686:15:    expected void [noderef] *iov_base<asn:1>
> > fs/bio.c:686:15:    got void [noderef] *<noident>
> > from the first form (cast to __user void *).  Lovely...
> > 
> > OK, I think I know what's going on there, will fix.
> 
> What happens is actually pretty simple - we get address_space(1) handled
> in declaration_specifiers(), which sets ctype->as to 1.  Then we see
> "void" and eventually get to
>                         ctype->base_type = type;
>                 }
> 
>                 check_modifiers(&token->pos, s, ctype->modifiers);
>                 apply_ctype(token->pos, &thistype, ctype);
> with thistype coming from lookup for "void".  And that, of course, has
> zero ->as.  Now apply_ctype merrily buggers ctype->as and we have 0...
> 
> So AFAICS proper fix for sparse should be to check thistype->as to see
> if it really has any intention to change ->as.  ACK?

PS: obvious testcase for that one:

#define X __attribute__((address_space(1)))    
void X *p;
void X *q;
void foo(unsigned long n)
{
        p = (void X *)n;
        q = (X void *)n;
}