Messages in this thread | | | From | Paul Wagland <> | Subject | Re: [PATCH][2.6.6-rc3] gcc-3.4.0 fixes | Date | Thu, 29 Apr 2004 22:46:19 +0200 |
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On Apr 29, 2004, at 11:30, 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?
http://es-sun2.fernuni-hagen.de/cgi-bin/info2html?(gcc)Subscripting
The ability to manipulate a cast was always a gcc extension, whether by design or feature I am not sure. The problem is that it breaks C++ templates in a bad way. Here is where the extension is documented for GCC 3.3.3
http://gcc.gnu.org/onlinedocs/gcc-3.3.3/gcc/Lvalues.html
This extension is now obsoleted.
> Previous code was agnostic to type of ptr, but you code presume ptr > being char pointer (to effectively increment by 4 bytes).
Yes, and the previous code assumed that that ptr was not a pointer to a 64 bit value, since dereferencing it on most platforms would then explode. I bet that both assumptions are just as safe ;-) However if you really wanted to be safe then you could do
ptr += sizeof (__32) / sizeof (*ptr);
Again, assuming that we are not using a greater then 4 byte ptr*, since otherwise it would not increment... But personally I think that this is not required.
Cheers, Paul [unhandled content-type:application/pgp-signature]
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