linux-kernel - Re: [PATCH RESEND] virtio: Fix typecast of pointer in vring

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Date:	Sun, 5 Jul 2015 12:58:53 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Thomas Huth <thuth@...hat.com>
Cc:	virtualization@...ts.linux-foundation.org,
	linux-api@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] virtio: Fix typecast of pointer in vring_init()

On Thu, Jul 02, 2015 at 09:21:22AM +0200, Thomas Huth wrote:
> The virtio_ring.h header is used in userspace programs (ie. QEMU),
> too. Here we can not assume that sizeof(pointer) is the same as
> sizeof(long), e.g. when compiling for Windows, so the typecast in
> vring_init() should be done with (uintptr_t) instead of (unsigned long).
> 
> Signed-off-by: Thomas Huth <thuth@...hat.com>

This seems to break some userspace too:

  INSTALL usr/include/linux/ (413 files)
  CHECK   usr/include/linux/ (413 files)
  HOSTCC  Documentation/accounting/getdelays
  HOSTCC  Documentation/connector/ucon
  HOSTCC  Documentation/mic/mpssd/mpssd.o
In file included from Documentation/mic/mpssd/mpssd.c:36:0:
./usr/include/linux/virtio_ring.h: In function ‘vring_init’:
./usr/include/linux/virtio_ring.h:146:24: error: ‘uintptr_t’ undeclared
(first use in this function)
  vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] +
sizeof(__virtio16)
                        ^
./usr/include/linux/virtio_ring.h:146:24: note: each undeclared
identifier is reported only once for each function it appears in
scripts/Makefile.host:108: recipe for target
'Documentation/mic/mpssd/mpssd.o' failed
make[3]: *** [Documentation/mic/mpssd/mpssd.o] Error 1
scripts/Makefile.build:403: recipe for target 'Documentation/mic/mpssd'
failed
make[2]: *** [Documentation/mic/mpssd] Error 2
scripts/Makefile.build:403: recipe for target 'Documentation/mic' failed
make[1]: *** [Documentation/mic] Error 2


E.g. fuse.h has this code:
#ifdef __KERNEL__
#include <linux/types.h>
#else
#include <stdint.h>
#endif

Maybe we need something similar.

> ---
>  include/uapi/linux/virtio_ring.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/virtio_ring.h b/include/uapi/linux/virtio_ring.h
> index 915980a..8682551 100644
> --- a/include/uapi/linux/virtio_ring.h
> +++ b/include/uapi/linux/virtio_ring.h
> @@ -143,7 +143,7 @@ static inline void vring_init(struct vring *vr, unsigned int num, void *p,
>  	vr->num = num;
>  	vr->desc = p;
>  	vr->avail = p + num*sizeof(struct vring_desc);
> -	vr->used = (void *)(((unsigned long)&vr->avail->ring[num] + sizeof(__virtio16)
> +	vr->used = (void *)(((uintptr_t)&vr->avail->ring[num] + sizeof(__virtio16)
>  		+ align-1) & ~(align - 1));
>  }
>  
> -- 
> 1.8.3.1
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