Re: [Qemu-devel] [PATCH] Fix conversions from pointer to int and vice versa

[Markus Armbruster <armbru@redhat.com>]

Stefan Weil <weil@mail.berlios.de> writes:

> Here the int values fds[0], sigfd, s, sock and fd are converted
> to void pointers which are later converted back to an int value.
>
> These conversions should always use intptr_t instead of unsigned long.
>
> They are needed for environments where sizeof(long) != sizeof(void *).

To be precise: when you want to cast a pointer to a signed integer type
and back without loss, intptr_t is the signed integer type to use.

But here we're dealing with the opposite case: cast int to pointer and
back.

> Signed-off-by: Stefan Weil <weil@mail.berlios.de>
> ---
>  cpus.c           |    8 ++++----
>  migration-tcp.c  |    4 ++--
>  migration-unix.c |    4 ++--
>  qemu-char.c      |    4 ++--
>  4 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/cpus.c b/cpus.c
> index 0f33945..3c4e1b8 100644
> --- a/cpus.c
> +++ b/cpus.c
> @@ -267,7 +267,7 @@ static void qemu_event_increment(void)
>  
>  static void qemu_event_read(void *opaque)
>  {
> -    int fd = (unsigned long)opaque;
> +    int fd = (intptr_t)opaque;
>      ssize_t len;
>      char buffer[512];
>  

Why can't you cast straight to int?

> @@ -295,7 +295,7 @@ static int qemu_event_init(void)
>          goto fail;
>      }
>      qemu_set_fd_handler2(fds[0], NULL, qemu_event_read, NULL,
> -                         (void *)(unsigned long)fds[0]);
> +                         (void *)(intptr_t)fds[0]);
>  
>      io_thread_fd = fds[1];
>      return 0;

Why can't you cast straight to void *?

[More of the same snipped...]