Re: [PATCH] Add SYSCALL_LONG/SYSCALL_ULONG to pass long to syscall [BZ #25810]

[Florian Weimer <fw@deneb.enyo.de>]

* H. J. Lu:

> On Sun, Apr 12, 2020 at 1:44 PM Florian Weimer <fw@deneb.enyo.de> wrote:
>>
>> * H. J. Lu:
>>
>> > nohup: ignoring input and appending output to 'nohup.out'
>> > gnu-tools-1:pts/5[130]> m nohup.out
>> > In file included from ../sysdeps/x86_64/nptl/tls.h:28,
>> >                  from ../include/errno.h:25,
>> >                  from ../sysdeps/unix/sysv/linux/fexecve.c:18:
>> > ../sysdeps/unix/sysv/linux/fexecve.c: In function ‘fexecve’:
>> > ../sysdeps/unix/sysv/linux/x86_64/x32/sysdep.h:56:6: error: cast from pointer to
>> >  integer of different size [-Werror=pointer-to-int-cast]
>> >    56 |    : (long long int) (X))
>> >       |      ^
>>
>> Please try something like this:
>>
>> #define ARGIFY(X)                                                       \
>>   ({                                                                    \
>>     _Pragma ("GCC diagnostic push");                                    \
>>     _Pragma ("GCC diagnostic ignored \"-Wpointer-to-int-cast\"");       \
>>     (sizeof (X) <= 4 && (__typeof__ (X)) 0 < (__typeof__ (X)) -1)       \
>>       ? (long long int) (unsigned long int) (X)                         \
>>       : (long int long) (X);                                            \
>>     _Pragma ("GCC diagnostic pop");                                     \
>>   })
>>
>> (__builtin_choose_expr does not work because it only suppresses
>> errors, not warnings.)
>>
>> It may not work in some cases because (__typeof__ (X)) 0 is not valid
>> if X is an array.
>
> It compiles, but doesn't work.  We need to cast the input of
>
> #define TYPEFY(X, name) __typeof__ ((X) - (X)) name
> #define ARGIFY(X) ((__typeof__ ((X) - (X))) (X))
>
> to unsigned long long.

Why does it fail?  Are there any arguments besides pointers which must
not be sign-extended to 64 bits?  According to syscall(2), I don't
think, so I still think we can make this work if we just avoid
sign-extending pointers.