Re: [Xen-devel] Build errors with latest xen-unstable from staging

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Sun, 2011-02-06 at 19:01 +0000, Kamala Narasimhan wrote:
> FYI - Pulled the latest xen-unstable from staging to sync some patches and got
> these trivial errors while compiling -
> 
> xl_cmdimpl.c: In function âprint_domain_vcpuinfoâ:
> xl_cmdimpl.c:3351: warning: âfirstsetâ may be used uninitialized in this 
> function
> xl_cmdimpl.c:3351: note: âfirstsetâ was declared here
> xl_cmdimpl.c:3350: warning: âbitmaskâ may be used uninitialized in this 
> function
> xl_cmdimpl.c:3350: note: âbitmaskâ was declared here
> xl_cmdimpl.c:3350: warning: âpmapâ may be used uninitialized in this function
> xl_cmdimpl.c:3350: note: âpmapâ was declared here
> 
> GCC version - 4.2.4.  Initializing the three variables it complained about 
> fixed
> the issue.

They are actually initialised before use, during the first pass through
the for loop when i==0 and state==0, but I can see how gcc would be
unable to figure that out (in fact I'm not sure about firstset myself).

In the Linux kernel they have a macro to annotate such instances:
        /*
         * A trick to suppress uninitialized variable warning without 
generating any
         * code
         */
        #define uninitialized_var(x) x = x
        
Do we want something similar?

>   If this trivial change should require a signed off line, here it is
> - Signed-off-by: Kamala Narasimhan <kamala.narasimhan@xxxxxxxxxx>

Always just assume a change does.

Ian.
> 
> diff -r 7ada6faef565 tools/libxl/xl_cmdimpl.c
> --- a/tools/libxl/xl_cmdimpl.c        Sun Feb 06 17:26:31 2011 +0000
> +++ b/tools/libxl/xl_cmdimpl.c        Sun Feb 06 13:53:50 2011 -0500
> @@ -3347,8 +3347,8 @@ static void print_bitmap(uint8_t *map, i
>  static void print_bitmap(uint8_t *map, int maplen, FILE *stream)
>  {
>      int i;
> -    uint8_t pmap, bitmask;
> -    int firstset, state = 0;
> +    uint8_t pmap = 0, bitmask = 0;
> +    int firstset = 0, state = 0;
> 
>      for (i = 0; i < maplen; i++) {
>          if (i % 8 == 0) {
> 
> Kamala
> 
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