V2 [PATCH 2/3] x32: Properly pass long to syscall [BZ #25810]

[H.J. Lu]

On Mon, Apr 13, 2020 at 2:13 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>
> * H. J. Lu via Libc-alpha:
>
> >> > diff --git a/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h b/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
> >> > index 2b5cf0c0ea..67335c2a7f 100644
> >> > --- a/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
> >> > +++ b/sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h
> >> > @@ -44,6 +44,20 @@
> >> >  # define ZERO_EXTEND_5 movl %r8d, %r8d;
> >> >  # undef ZERO_EXTEND_6
> >> >  # define ZERO_EXTEND_6 movl %r9d, %r9d;
> >> > +#else /*! __ASSEMBLER__ */
> >> > +# undef ARGIFY
> >> > +/* Enforce zero-extension for pointers and array system call arguments.
> >> > +   For integer types, extend to int64_t (the full register) using a
> >> > +   regular cast, resulting in zero or sign extension based on the
> >> > +   signedness of the original type.  */
> >> > +# define ARGIFY(X) \
> >> > + ({                                                                  \
> >> > +    _Pragma ("GCC diagnostic push");                                 \
> >> > +    _Pragma ("GCC diagnostic ignored \"-Wpointer-to-int-cast\"");    \
> >> > +    (__builtin_classify_type (X) == 5                                        \
> >> > +     ? (uintptr_t) (X) : (int64_t) (X));                             \
> >> > +    _Pragma ("GCC diagnostic pop");                                  \
> >> > +  })
> >> >  #endif       /* __ASSEMBLER__ */
> >> >
> >> >  #endif /* linux/x86_64/x32/sysdep.h */
> >>
> >> I face a similar issue when fixing BZ#12683 for x32, and one possible
> >> solution I found was:
> >>
> >>   #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;                                                      \
> >>   })
> >
> > This is similar to what I have checked in.
>
> I think Adhemerval specifically meant the additional cast using
> __typeof__ to suppress the warning (which I did not think of).

His patch:

https://sourceware.org/pipermail/libc-alpha/2020-April/112520.html

also needs to suppress -Wpointer-to-int-cast

> The _Pragma construct as written is a Clang porting hazard because it
> causes the statement expression to return void (which is a Clang/GCC
> discrepancy).  Rather than introducing a temporary, using the
> __typeof__ hack is probably the better way of fixing it.

I don't think it works on array.

-- 
H.J.