Re: [PATCH][2.6.6-rc3] gcc-3.4.0 fixes

[Ihar 'Philips' Filipau]

Denis Vlasenko wrote:
> On Thursday 29 April 2004 12:30, Ihar 'Philips' Filipau wrote:
>
> > Mikael Pettersson wrote:
> >
> > > This patch fixes three warnings from gcc-3.4.0 in 2.6.6-rc3:
> > > - drivers/char/ftape/: use of cast-as-lvalue
> > > 		if (get_unaligned((__u32*)ptr)) {
> > > -			++(__u32*)ptr;
> > > +			ptr += sizeof(__u32);
> > > 		} else {
> >
> >   Can anyone explain what is the problem with this?
> >   To me it seems pretty ligitimate code - why it was outlawed in gcc 3.4?
>
>
> cast is not a lvalue. ++(__u32*)ptr is nonsense, just like ++4.

  Yes. I see. C goes in direction of C++.
  For me cast in C is always "forget original type and assume this type."
  From this standpoint it makes a lot of sense. Is just like
((stuct { char a,b,c,d;})4).a - never tryed it in gcc (3.3 does not 
accept it), but IIRC was possible on old PC C compilers - Turbo C 2/3 - 
not sure name/version, but I used it. (Yes! recalled - M$VC/winbase.h 
use this kind of macros for manipulating bytes/words/dwords/etc)
  And in old C classes it was always said that in C you can convert 
anything to everything, it just size of types must be the same.

  Why not after all?

> ptr = (void*) ((char*)ptr + sizeof(__u32));

  No Nice, But Accepted.

  I have just checked my code base - I do not use this feature in any 
way ;-)

--
Ihar 'Philips' Filipau  / with best regards from Saarbruecken.
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