| |
|
 |
|
 |
|
|
|
| |
|
|
xen-devel
Re: [Xen-devel] Build errors with latest xen-unstable from staging
Ian Campbell wrote:
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 ‘print_domain_vcpuinfo’:
xl_cmdimpl.c:3351: warning: ‘firstset’ may be used uninitialized in this
function
xl_cmdimpl.c:3351: note: ‘firstset’ was declared here
xl_cmdimpl.c:3350: warning: ‘bitmask’ may be used uninitialized in this function
xl_cmdimpl.c:3350: note: ‘bitmask’ was declared here
xl_cmdimpl.c:3350: warning: ‘pmap’ may be used uninitialized in this function
xl_cmdimpl.c:3350: note: ‘pmap’ 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).
I agree with Ian, looking through the code again I can confirm that they
are _not_ used uninitialized. Even firstset is set when the state
switches from 0 to 1 and is only used later in state 1 and 3, so it is safe.
It seems like the compiler is not smart enough to recognize this,
especially the modulo operation could be a barrier for the analysis, I
think.
According to the manpage those warning are only emitted on -O, which I
left out for my testing, so I didn't spot this warning. Sorry.
To appease the compiler I would ack the fix, though from an academic
point of view it is not necessary.
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?
I don't think so. x = x looks more like a hack, if we can easily
initialize the variables, we should do so.
Regards,
Andre.
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
--
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel
|
|
|
| |
|
Home