Il ven 9 mag 2025, 09:58 Daniel P. Berrangé <berra...@redhat.com> ha
scritto:
> On Fri, May 09, 2025 at 07:48:57AM +0200, Markus Armbruster wrote:
> > Nabih Estefan <nabiheste...@google.com> writes:
> >
> > > From: Peter Foley <pefo...@google.com>
> > >
> > > e.g.
> > > I 2025-02-28 09:51:05.240071-0800 624 stream.go:47
> qemu: Uninitialized value was created by an allocation of 'key_in_cur.i' in
> the stack frame
> > > I 2025-02-28 09:51:05.240187-0800 624 stream.go:47
> qemu: #0 0xaaaac49f489c in keyval_parse_one
> third_party/qemu/util/keyval.c:190:5
> > >
> > > Signed-off-by: Peter Foley <pefo...@google.com>
> > > Signed-off-by: Nabih Estefan <nabiheste...@google.com>
> > > ---
> > > util/keyval.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/util/keyval.c b/util/keyval.c
> > > index a70629a481..f33c64079d 100644
> > > --- a/util/keyval.c
> > > +++ b/util/keyval.c
> > > @@ -187,7 +187,7 @@ static const char *keyval_parse_one(QDict *qdict,
> const char *params,
> > > {
> > > const char *key, *key_end, *val_end, *s, *end;
> > > size_t len;
> > > - char key_in_cur[128];
> > > + char key_in_cur[128] = {};
> > > QDict *cur;
> > > int ret;
> > > QObject *next;
> >
> > Prior review of Peter's patch concluded this must be false positive:
> >
> https://lore.kernel.org/qemu-devel/14168384-ecdb-4c05-8267-ac5ef1c46...@redhat.com/
>
> While I agree with Paolo's reasoning, I think it is still worth adding an
> explicit initializer, because it makes it easier for both humans and
> machines
> to reason about correctless.
>
The problem is that, in the exact same (impossible) case there would have
to be another uninitialized variable, s. So the patch ends up making it
harder to understand what are the invariants of the function.
One should fix the compiler instead.
Paolo
> To reinforce that we don't have an actual bug though, also note that qemu
> unconditionally builds with -ftrivial-auto-var-init=zero. So if we happen
> to forget any, it won't cause a bug in the common case of a
> zero-initializer.
>
> With regards,
> Daniel
> --
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