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

["H.J. Lu" <hjl.tools@gmail.com>]

On Sat, Apr 11, 2020 at 7:45 AM Florian Weimer <fw@deneb.enyo.de> wrote:
>
> * H. J. Lu:
>
> > On Sat, Apr 11, 2020 at 3:01 AM Florian Weimer <fw@deneb.enyo.de> wrote:
> >>
> >> * H. J. Lu via Libc-alpha:
> >>
> >> > For inline syscalls, SYSCALL_LONG and SYSCALL_ULONG are introduced as
> >> > wrappers for long and unsigned long arguments.
> >>
> >> Do the arguments have the correct types?  Then I think you can do the
> >
> > Yes, they have correct types.  But it is not the problem.  Take this example:
> >
> > int munmap(void *addr, size_t length);
> >
> > The type of length is unsigned int (size_t) for x32 and is unsigned long
> > (64bit) in kernel.  We have no way to know the type which kernel expects.
>
> Is it possible to extend all 32-bit arguments?  Ot is this incorrect
> for negative int arguments, which must not have their upper bits set?

      ssize_t msgrcv(int msqid, void *msgp, size_t msgsz, long msgtyp,
                      int msgflg);

      * If msgtyp is 0, then the first message in the queue is read.

       * If  msgtyp  is greater than 0, then the first message in the queue of
         type msgtyp is read, unless MSG_EXCEPT was specified  in  msgflg,  in
         which case the first message in the queue of type not equal to msgtyp
         will be read.

       * If msgtyp is less than 0, then the first message in  the  queue  with
         the  lowest  type  less than or equal to the absolute value of msgtyp
         will be read.

In this syscall, msgtyp should be sign-extended to 64-bit.


H.J.

-- 
H.J.