On Wed, 2014-05-28 at 17:11 -0500, Cody P Schafer wrote:
> On Wed, May 28, 2014 at 5:05 PM, Cody P Schafer <d...@codyps.com> wrote:
> > On Wed, May 28, 2014 at 3:45 AM, David Laight <david.lai...@aculab.com>
> > wrote:
> >> From: Cody P Schafer
> >>> Rather manually specifying the size of the integer to be converted, key
> >>> off of the type size. Reduces duplicate size info and the occurance of
> >>> certain types of bugs (using the wrong sized conversion).
> >> ...
> >>> +#define be_to_cpu(v) \
> >>> + __builtin_choose_expr(sizeof(v) == sizeof(uint8_t) , v, \
> >>> + __builtin_choose_expr(sizeof(v) == sizeof(uint16_t),
> >>> be16_to_cpu(v), \
> >>> + __builtin_choose_expr(sizeof(v) == sizeof(uint32_t),
> >>> be32_to_cpu(v), \
> >>> + __builtin_choose_expr(sizeof(v) == sizeof(uint64_t),
> >>> be64_to_cpu(v), \
> >>> + (void)0))))
> >> ...
> >>
> >> I'm not at all sure that using the 'size' of the constant will reduce
> >> the number of bugs - it just introduces a whole new category of bugs.
> >
> > Certainly, if you mis-size the argument (and thus have missized one of
> > the variables containing the be value, probably a bug anyhow), there
> > will be problems.
> >
> > I put this interface together because of an actual bug I wrote into
> > the initial code of the hv_24x7 driver (resized a struct member
> > without adjusting the be*_to_cpu() sizing).
> > Having this "auto sizing" macro means I can avoid encoding the size of
> > a struct field in multiple places.
>
> To clarify, the point I'm making here is that this simply cuts out 1
> more place we can screw up endianness conversion sizing.
It does screw up other types when you do things like:
u8 foo = some_function();
cpu_to_be(foo + 1);
the return value is sizeof(int) not u8
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
