Re: [Xen-devel] [PATCH v2] libxc: Fix buffer length for get_suspend_file

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-03-18 at 13:58 +0000, Ian Jackson wrote:
> Declaring a formal parameter to have an array type doesn't result in
> the parameter actually having an array type.  The type is "adjusted"
> to a pointer.  (C99 6.9.1(7), 6.7.5.3.)
> 
> So the use of sizeof in xc_suspend.c:get_suspend_file was wrong.
> Instead, use the #define.  Also get rid of the array size, as it is
> misleading.
> 
> Newer versions of gcc warn about the erroneous code:
>   xc_suspend.c:39:25: error: argument to 'sizeof' in 'snprintf' call
>     is the same expression as the destination; did you mean to provide
>     an explicit length? [-Werror=sizeof-pointer-memaccess]
> 
> Reported-By: Julien Grall <julien.grall@xxxxxxxxxx>
> Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

Although I do wonder if it would be less error prone to push the size up
to a parameter to get_suspend_file where it is (presumably) near to the
declaration of the array.

> CC: Julien Grall <julien.grall@xxxxxxxxxx>
> 
> --
> v2: Actually change the declaration of buf.
> ---
>  tools/libxc/xc_suspend.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/libxc/xc_suspend.c b/tools/libxc/xc_suspend.c
> index 84ee139..200d381 100644
> --- a/tools/libxc/xc_suspend.c
> +++ b/tools/libxc/xc_suspend.c
> @@ -34,9 +34,9 @@
>  
>  #define SUSPEND_FILE_BUFLEN (sizeof(SUSPEND_LOCK_FILE) + 10)
>  
> -static void get_suspend_file(char buf[SUSPEND_FILE_BUFLEN], int domid)
> +static void get_suspend_file(char buf[], int domid)
>  {
> -    snprintf(buf, sizeof(buf), SUSPEND_LOCK_FILE, domid);
> +    snprintf(buf, SUSPEND_FILE_BUFLEN, SUSPEND_LOCK_FILE, domid);
>  }
>  
>  static int lock_suspend_event(xc_interface *xch, int domid, int *lockfd)



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel