[RFC,3/12] mach, hurd: Cast through uintptr_t

When casting between a pointer and an integer of a different size, GCC
emits a warning (which is escalated to a build failure by -Werror).
Indeed, if what you start with is a pointer, which you then cast to a
shorter integer and then back again, you're going to cut off some bits
of the pointer.

But if you start with an integer (such as mach_port_t), then cast it to
a longer pointer (void *), and then back to a shorter integer, you are
fine. To keep GCC happy, cast through an intermediary uintptr_t, which
is always the same size as a pointer.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
---
 htl/cthreads-compat.c |  5 +++--
 hurd/fopenport.c      | 15 ++++++++++-----
 hurd/hurd/port.h      |  2 +-
 hurd/port-cleanup.c   |  3 ++-
 hurd/vpprintf.c       |  6 ++++--
 mach/devstream.c      |  9 +++++----
 6 files changed, 25 insertions(+), 15 deletions(-)

Applied, thanks!

Sergey Bugaev, le dim. 12 févr. 2023 14:10:34 +0300, a ecrit:
> When casting between a pointer and an integer of a different size, GCC
> emits a warning (which is escalated to a build failure by -Werror).
> Indeed, if what you start with is a pointer, which you then cast to a
> shorter integer and then back again, you're going to cut off some bits
> of the pointer.
> 
> But if you start with an integer (such as mach_port_t), then cast it to
> a longer pointer (void *), and then back to a shorter integer, you are
> fine. To keep GCC happy, cast through an intermediary uintptr_t, which
> is always the same size as a pointer.
> 
> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
> ---
>  htl/cthreads-compat.c |  5 +++--
>  hurd/fopenport.c      | 15 ++++++++++-----
>  hurd/hurd/port.h      |  2 +-
>  hurd/port-cleanup.c   |  3 ++-
>  hurd/vpprintf.c       |  6 ++++--
>  mach/devstream.c      |  9 +++++----
>  6 files changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/htl/cthreads-compat.c b/htl/cthreads-compat.c
> index 55043a8b..2a0a95b6 100644
> --- a/htl/cthreads-compat.c
> +++ b/htl/cthreads-compat.c
> @@ -25,8 +25,9 @@ void
>  __cthread_detach (__cthread_t thread)
>  {
>    int err;
> +  pthread_t pthread = (pthread_t) (uintptr_t) thread;
>  
> -  err = __pthread_detach ((pthread_t) thread);
> +  err = __pthread_detach (pthread);
>    assert_perror (err);
>  }
>  weak_alias (__cthread_detach, cthread_detach)
> @@ -40,7 +41,7 @@ __cthread_fork (__cthread_fn_t func, void *arg)
>    err = __pthread_create (&thread, NULL, func, arg);
>    assert_perror (err);
>  
> -  return (__cthread_t) thread;
> +  return (__cthread_t) (uintptr_t) thread;
>  }
>  weak_alias (__cthread_fork, cthread_fork)
>  
> diff --git a/hurd/fopenport.c b/hurd/fopenport.c
> index 60afb445..be6aa30c 100644
> --- a/hurd/fopenport.c
> +++ b/hurd/fopenport.c
> @@ -28,9 +28,10 @@ readio (void *cookie, char *buf, size_t n)
>    mach_msg_type_number_t nread;
>    error_t err;
>    char *bufp = buf;
> +  io_t io = (io_t) (uintptr_t) cookie;
>  
>    nread = n;
> -  if (err = __io_read ((io_t) cookie, &bufp, &nread, -1, n))
> +  if (err = __io_read (io, &bufp, &nread, -1, n))
>      return __hurd_fail (err);
>  
>    if (bufp != buf)
> @@ -50,8 +51,9 @@ writeio (void *cookie, const char *buf, size_t n)
>  {
>    vm_size_t wrote;
>    error_t err;
> +  io_t io = (io_t) (uintptr_t) cookie;
>  
> -  if (err = __io_write ((io_t) cookie, buf, n, -1, &wrote))
> +  if (err = __io_write (io, buf, n, -1, &wrote))
>      return __hurd_fail (err);
>  
>    return wrote;
> @@ -65,7 +67,8 @@ seekio (void *cookie,
>  	off64_t *pos,
>  	int whence)
>  {
> -  error_t err = __io_seek ((file_t) cookie, *pos, whence, pos);
> +  io_t io = (io_t) (uintptr_t) cookie;
> +  error_t err = __io_seek (io, *pos, whence, pos);
>    return err ? __hurd_fail (err) : 0;
>  }
>  
> @@ -74,8 +77,9 @@ seekio (void *cookie,
>  static int
>  closeio (void *cookie)
>  {
> +  io_t io = (io_t) (uintptr_t) cookie;
>    error_t error = __mach_port_deallocate (__mach_task_self (),
> -					  (mach_port_t) cookie);
> +					  io);
>    if (error)
>      return __hurd_fail (error);
>    return 0;
> @@ -127,6 +131,7 @@ __fopenport (mach_port_t port, const char *mode)
>        return NULL;
>      }
>  
> -  return fopencookie ((void *) port, mode, funcsio);
> +  return fopencookie ((void *) (uintptr_t) port,
> +                      mode, funcsio);
>  }
>  weak_alias (__fopenport, fopenport)
> diff --git a/hurd/hurd/port.h b/hurd/hurd/port.h
> index fdba8db5..1e473978 100644
> --- a/hurd/hurd/port.h
> +++ b/hurd/hurd/port.h
> @@ -96,7 +96,7 @@ _hurd_port_locked_get (struct hurd_port *port,
>    if (result != MACH_PORT_NULL)
>      {
>        link->cleanup = &_hurd_port_cleanup;
> -      link->cleanup_data = (void *) result;
> +      link->cleanup_data = (void *) (uintptr_t) result;
>        _hurd_userlink_link (&port->users, link);
>      }
>    __spin_unlock (&port->lock);
> diff --git a/hurd/port-cleanup.c b/hurd/port-cleanup.c
> index 08ab3d47..ad43b830 100644
> --- a/hurd/port-cleanup.c
> +++ b/hurd/port-cleanup.c
> @@ -26,7 +26,8 @@
>  void
>  _hurd_port_cleanup (void *cleanup_data, jmp_buf env, int val)
>  {
> -  __mach_port_deallocate (__mach_task_self (), (mach_port_t) cleanup_data);
> +  mach_port_t port = (mach_port_t) (uintptr_t) cleanup_data;
> +  __mach_port_deallocate (__mach_task_self (), port);
>  }
>  
>  /* We were cancelled while using a port, and called from the cleanup unwinding.
> diff --git a/hurd/vpprintf.c b/hurd/vpprintf.c
> index fe734946..010f04ca 100644
> --- a/hurd/vpprintf.c
> +++ b/hurd/vpprintf.c
> @@ -25,8 +25,9 @@
>  static ssize_t
>  do_write (void *cookie,	const char *buf, size_t n)
>  {
> +  io_t io = (io_t) (uintptr_t) cookie;
>    vm_size_t amount = n;
> -  error_t error = __io_write ((io_t) cookie, buf, n, -1, &amount);
> +  error_t error = __io_write (io, buf, n, -1, &amount);
>    if (error)
>      return __hurd_fail (error);
>    return n;
> @@ -51,7 +52,8 @@ vpprintf (io_t port, const char *format, va_list arg)
>  #endif
>  
>    _IO_cookie_init (&temp_f.cfile, _IO_NO_READS,
> -		   (void *) port, (cookie_io_functions_t) { write: do_write });
> +                   (void *) (uintptr_t) port,
> +                   (cookie_io_functions_t) { write: do_write });
>  
>    done = __vfprintf_internal (&temp_f.cfile.__fp.file, format, arg, 0);
>  
> diff --git a/mach/devstream.c b/mach/devstream.c
> index 09272d10..cfa9a4f4 100644
> --- a/mach/devstream.c
> +++ b/mach/devstream.c
> @@ -28,7 +28,7 @@
>  static ssize_t
>  devstream_write (void *cookie, const char *buffer, size_t n)
>  {
> -  const device_t dev = (device_t) cookie;
> +  const device_t dev = (device_t) (uintptr_t) cookie;
>  
>    int write_some (const char *p, size_t to_write)
>      {
> @@ -83,7 +83,7 @@ devstream_write (void *cookie, const char *buffer, size_t n)
>  static ssize_t
>  devstream_read (void *cookie, char *buffer, size_t to_read)
>  {
> -  const device_t dev = (device_t) cookie;
> +  const device_t dev = (device_t) (uintptr_t) cookie;
>  
>    kern_return_t err;
>    mach_msg_type_number_t nread = to_read;
> @@ -112,7 +112,8 @@ devstream_read (void *cookie, char *buffer, size_t to_read)
>  static int
>  dealloc_ref (void *cookie)
>  {
> -  if (__mach_port_deallocate (mach_task_self (), (mach_port_t) cookie))
> +  const device_t dev = (device_t) (uintptr_t) cookie;
> +  if (__mach_port_deallocate (mach_task_self (), dev))
>      {
>        errno = EINVAL;
>        return -1;
> @@ -131,7 +132,7 @@ mach_open_devstream (mach_port_t dev, const char *mode)
>        return NULL;
>      }
>  
> -  stream = _IO_fopencookie ((void *) dev, mode,
> +  stream = _IO_fopencookie ((void *) (uintptr_t) dev, mode,
>  			    (cookie_io_functions_t) { write: devstream_write,
>  						      read: devstream_read,
>  						      close: dealloc_ref });
> -- 
> 2.39.1
> 
>