On Wed, Jun 28, 2017 at 01:21:43PM +0200, Thomas Gleixner wrote:
> On Wed, 28 Jun 2017, Dmitry Vyukov wrote:
> > On Wed, Jun 28, 2017 at 1:10 PM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> > >> In my case I ended up with something like:
> > >>
> > >> __typeof__(foo) __ptr = __ptr;
> > >>
> > >> which compiler decided to turn into 0.
> > >>
> > >> Thank you, macros.
> > >>
> > >> We can add more underscores, but the problem can happen again. Should
> > >> we prefix current function/macro name to all local vars?..
> > >
> > > Actually we can void that ___ptr dance completely.
> > >
> > > Thanks,
> > >
> > > tglx
> > >
> > > 8<--------------------
> > >
> > > --- a/include/asm-generic/atomic-instrumented.h
> > > +++ b/include/asm-generic/atomic-instrumented.h
> > > @@ -359,37 +359,32 @@ static __always_inline bool atomic64_add
> > >
> > > #define cmpxchg(ptr, old, new) \
> > > ({ \
> > > - __typeof__(ptr) ___ptr = (ptr); \
> > > - kasan_check_write(___ptr, sizeof(*___ptr)); \
> > > + kasan_check_write((ptr), sizeof(*(ptr))); \
> > > arch_cmpxchg((ptr), (old), (new)); \
> > > })
> > >
> > > #define sync_cmpxchg(ptr, old, new) \
> > > ({ \
> > > - __typeof__(ptr) ___ptr = (ptr); \
> > > - kasan_check_write(___ptr, sizeof(*___ptr)); \
> > > - arch_sync_cmpxchg(___ptr, (old), (new)); \
> > > + kasan_check_write((ptr), sizeof(*(ptr))); \
> > > + arch_sync_cmpxchg((ptr), (old), (new)); \
> > > })
> > >
> > > #define cmpxchg_local(ptr, old, new) \
> > > ({ \
> > > - __typeof__(ptr) ____ptr = (ptr); \
> > > - kasan_check_write(____ptr, sizeof(*____ptr)); \
> > > - arch_cmpxchg_local(____ptr, (old), (new)); \
> > > + kasan_check_write((ptr), sizeof(*(ptr))); \
> > > + arch_cmpxchg_local((ptr), (old), (new)); \
> >
> >
> > /\/\/\/\/\/\/\/\/\/\/\/\
> >
> > These are macros.
> > If ptr is foo(), then we will call foo() twice.
>
> Sigh, is that actually used?
For better or worse, we can't rule it out.
We'd risk even more subtle bugs in future trying to rely on that not
being the case. :/
> That's all insane. The whole crap gets worse because:
>
> cmpxchg() can be used on u8, u16, u32 ....
Yup, that's the whole reason for the macro insanity in the fist place.
Anoother option is something like:
static inline unsigned long
cmpxchg_size(unsigned long *ptr, unsigned long old, unsigned long new, int size)
{
kasan_check_write(ptr, size);
switch (size) {
case 1:
return arch_cmpxchg((u8 *)ptr, (u8)old, (u8)new);
case 2:
return arch_cmpxchg((u16 *)ptr, (u16)old, (u16)new);
case 4:
return arch_cmpxchg((u32 *)ptr, (u32)old, (u32)new);
case 8:
return arch_cmpxchg((u64 *)ptr, (u64)old, (u64)new);
}
BUILD_BUG();
}
#define cmpxchg(ptr, old, new) \
cmpxchg_size(ptr, old, new, sizeof(*ptr))
Thanks,
Mark.
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