[PATCH v4 04/21] nptl: x32: Fix Race conditions in pthread cancellation [BZ#12683]

[H.J. Lu]

On Tue, Apr 7, 2020 at 6:55 AM Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
>
> On 07/04/2020 10:41, H.J. Lu wrote:
> > On Tue, Apr 7, 2020 at 6:40 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >>
> >> On Tue, Apr 7, 2020 at 6:33 AM Adhemerval Zanella
> >> <adhemerval.zanella@linaro.org> wrote:
> >>>
> >>>
> >>>
> >>> On 07/04/2020 09:54, H.J. Lu wrote:
> >>>> On Tue, Apr 7, 2020 at 5:47 AM Adhemerval Zanella via Libc-alpha
> >>>> <libc-alpha@sourceware.org> wrote:
> >>>>>
> >>>>>
> >>>>>
> >>>>> On 03/04/2020 18:22, Joseph Myers wrote:
> >>>>>> On Fri, 3 Apr 2020, Adhemerval Zanella via Libc-alpha wrote:
> >>>>>>
> >>>>>>> This patches adds the x32 modification required for the BZ#12683.
> >>>>>>> It follows the x86_64-x32 ABI and pointers are zero-extended.
> >>>>>>> However, compiler may not see such cases and accuse a cast from pointer
> >>>>>>> to integer of different size and for such cases the warning is
> >>>>>>> explict disabled.
> >>>>>>
> >>>>>> MIPS n32 uses an intermediate cast to (__typeof__ ((X) - (X))), so that a
> >>>>>> conversion to a different size is never directly from a pointer type.
> >>>>>> Does something like that help here to avoid the warning without needing to
> >>>>>> use diagnostic pragmas?
> >>>>>
> >>>>> The intermediate cast to (__typeof__ ((X) - (X))) is not suffice for x32
> >>>>> (the resulting argumetn it will passed as function argument instead of
> >>>>> asm input).  I have replaced with:
> >>>>>
> >>>>>   #define __SSC(__x)                                              \
> >>>>>   ({                                                            \
> >>>>>     __syscall_arg_t __arg = sizeof (1 ? (__x) : 0ULL) < 8       \
> >>>>>       ? (unsigned long int) (uintptr_t)(__x)                    \
> >>>>>       : (__syscall_arg_t) (__typeof__ ((__x) - (__x))) (__x);   \
> >>>>>     __arg;                                                      \
> >>>>>   })
> >>>>>
> >>>>
> >>>> Have you looked at libc-pointer-arith.h?
> >>>
> >>> That was my first approach, by using cast_to_integer macro. I tried to
> >>> change its internals to zero extend pointers correctly, but I couldn't
> >>> find a easier way without also adding the cast point suppression
> >>> warning in this original patch.
> >>
> >> Have you looked at sysdeps/unix/sysv/linux/x86_64/sysdep.h?
> >>
> >
> > /* Create a variable 'name' based on type 'X' to avoid explicit types.
> >    This is mainly used set use 64-bits arguments in x32.   */
> > #define TYPEFY(X, name) __typeof__ ((X) - (X)) name
> > /* Explicit cast the argument to avoid integer from pointer warning on
> >    x32.  */
> > #define ARGIFY(X) ((__typeof__ ((X) - (X))) (X))
> >
>
> Yes, I was the one that actually added them (78ca091cdd2). But for this
> case, the issue is it requires another implicit cast on the
> __syscall_cancel call itself.  The difference here is the call is not
> done through an asm input anymore.

Do you have a git branch I can try?

-- 
H.J.