On Sat, 24 Nov 2007 17:22:36 +0000
Luciano Rocha <[EMAIL PROTECTED]> wrote:
> On Sat, Nov 24, 2007 at 05:19:31PM +0100, Pierre Ossman wrote:
> > It most certainly does not. gcc will assume that an int* has int alignment.
> > memcpy() is a builtin, which gcc can translate to pretty much anything. And
> > C specifies that a pointer to foo, will point to a real object of type foo,
> > so gcc can't be blamed for the unsafe typecasts. I have tested this the
> > hard way, so this is not just speculation.
>
> Yes, on *int and other assumed aligned pointers, gcc uses its internal
> version.
>
> However, my point is that those pointers, unless speaking of packed
> structures, can safely be assumed aligned, while char*/void* can't.
>
I get the sensation we're violently in agreement here, just misunderstanding
each other. :)
_My_ point was that the documentation should mention that normal, unpacked C
objects have alignments that influence the code generated by
__builtin_memcpy(). As such, one should always make sure to have either src or
dst be char*/void* when alignment cannot be guaranteed. The example in the
documentation has this, but it isn't explicit that this is required.
Rgds
--
-- Pierre Ossman
Linux kernel, MMC maintainer http://www.kernel.org
PulseAudio, core developer http://pulseaudio.org
rdesktop, core developer http://www.rdesktop.org
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