[PATCH] eliminate compiler warning for xpc_channel.c

[PATCH] eliminate compiler warning for xpc_channel.c

[Dean Nelson]

Placate a compiler warning that 'msg' may be used uninitialized in
function xpc_initiate_allocate().

Signed-off-by: Dean Nelson <dcn@sgi.com>


Index: linux-2.6/arch/ia64/sn/kernel/xpc_channel.c
=================================--- linux-2.6.orig/arch/ia64/sn/kernel/xpc_channel.c	2006-04-03 08:26:22.000000000 -0500
+++ linux-2.6/arch/ia64/sn/kernel/xpc_channel.c	2006-04-04 08:25:51.691831163 -0500
@@ -1831,7 +1831,7 @@
 {
 	struct xpc_partition *part = &xpc_partitions[partid];
 	enum xpc_retval ret = xpcUnknownReason;
-	struct xpc_msg *msg;
+	struct xpc_msg *msg = msg;
 
 
 	DBUG_ON(partid <= 0 || partid >= XP_MAX_PARTITIONS);

RE: [PATCH] eliminate compiler warning for xpc_channel.c

[Luck, Tony]

> Placate a compiler warning that 'msg' may be used uninitialized in
> function xpc_initiate_allocate().

Which version of which compiler ... at first glance the code looks
trivially OK (&msg is passed to xpc_allocate_msg() before it is used).
On closer inspection I assume that the compiler must have inlined
xpc_allocate_msg() in order to detect this, and there are four "return"
statements in there that can return w/o doing the initialization. So
the warning is real, and we are not just "placating" the compiler.

-	struct xpc_msg *msg;
+	struct xpc_msg *msg = msg;

Did you mean to say "*msg = NULL"?

-Tony

Re: [PATCH] eliminate compiler warning for xpc_channel.c

[Matthew Wilcox]

On Tue, Apr 04, 2006 at 07:23:32AM -0700, Luck, Tony wrote:
> -	struct xpc_msg *msg;
> +	struct xpc_msg *msg = msg;
> 
> Did you mean to say "*msg = NULL"?

this is actually an ANSI-permitted idiom for shutting up compiler
warnings while not actually initialising the variable.

RE: [PATCH] eliminate compiler warning for xpc_channel.c

[Luck, Tony]

>> Did you mean to say "*msg = NULL"?
>
> this is actually an ANSI-permitted idiom for shutting up compiler
> warnings while not actually initialising the variable.

So I learned something new today!

But then this patch is wrong ... it shuts the compiler up
and leaves 4 ways that xpc_allocate_msg() can return without doing
the initialization, so that msg will be used uninitialized.

-Tony

Re: [PATCH] eliminate compiler warning for xpc_channel.c

[Dean Nelson]

On Tue, Apr 04, 2006 at 07:34:08AM -0700, Luck, Tony wrote:
> >> Did you mean to say "*msg = NULL"?
> >
> > this is actually an ANSI-permitted idiom for shutting up compiler
> > warnings while not actually initialising the variable.
> 
> So I learned something new today!
> 
> But then this patch is wrong ... it shuts the compiler up
> and leaves 4 ways that xpc_allocate_msg() can return without doing
> the initialization, so that msg will be used uninitialized.

You are correct: "*msg = NULL" is the right answer.

The compiler being used is: "gcc (GCC) 4.1.0 (SUSE Linux)".

In the past when I've seen complier warnings of this nature, it usually
(but not always) turned out that the compiler was unable to 'see' that
things were really okay. In this particular case, I hadn't seen this
warning until just yesterday (my build machine was just updated a few
days ago), and since nothing in this area of the code had changed for
some time now, I just assumed that the compiler was not seeing things
properly. It didn't occur to me that xpc_allocate_msg() was possibly
being inlined and thus the compiler was giving a correct warning that
should not be ignored.

Do you want a new patch, or are you comfortable with switching the
'msg' to a 'NULL'?

Thanks for looking more closely than I obviously did.

Dean

RE: [PATCH] eliminate compiler warning for xpc_channel.c

[Luck, Tony]

> Do you want a new patch, or are you comfortable with switching the
> 'msg' to a 'NULL'?

I'll switch it to NULL.

-Tony