Re: [PATCH] vl: Fix an assert failure in error path

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Jun 09, 2021 at 02:09:47PM +0200, Markus Armbruster wrote:
> Paolo Bonzini <pbonzini@redhat.com> writes:
> 
> > On 10/06/21 10:47, Zhenzhong Duan wrote:
> >> Based on the description of error_setg(), the local variable err in
> >> qemu_maybe_daemonize() should be initialized to NULL.
> >> Without fix, the uninitialized *errp triggers assert failure which
> >> doesn't show much valuable information.
> >> Before the fix:
> >> qemu-system-x86_64: ../util/error.c:59: error_setv: Assertion `*errp == NULL' failed.
> >> After fix:
> >> qemu-system-x86_64: cannot create PID file: Cannot open pid file: Permission denied
> >> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> >> ---
> >>   softmmu/vl.c | 2 +-
> >>   1 file changed, 1 insertion(+), 1 deletion(-)
> >> diff --git a/softmmu/vl.c b/softmmu/vl.c
> >> index 326c1e9080..feb4d201f3 100644
> >> --- a/softmmu/vl.c
> >> +++ b/softmmu/vl.c
> >> @@ -2522,7 +2522,7 @@ static void qemu_process_help_options(void)
> >>     static void qemu_maybe_daemonize(const char *pid_file)
> >>   {
> >> -    Error *err;
> >> +    Error *err = NULL;
> 
> Common mistake, I'm afraid.

Initializing isn't likely to be a performance impact, so I'd think
we should make 'checkpatch.pl' complain about any 'Error *' variable
that is not initialized to NULL, as a safety net, even if not technically
required in some cases.

Regards,
Daniel
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