Re: [Qemu-devel] [PATCH V2] build: remove compile warning

[Wenchao Xia]

  I insist to remove compile warning since I want gcc check my code with
strict rule.

> Wenchao Xia <address@hidden> writes:
>
> > This patch simply remove "variable may be used uninitialized" warning.
> >
> > Signed-off-by: Wenchao Xia <address@hidden>
> > ---
> > V2: Address Stefan and Peter's comments, use 0 in send_msg() instead of
> > initialize mhHeader.
> >
> >   libcacard/vscclient.c |    3 +--
> >   util/iov.c            |    2 +-
> >   2 files changed, 2 insertions(+), 3 deletions(-)

> > diff --git a/util/iov.c b/util/iov.c
> > index cc6e837..b91cfb9 100644
> > --- a/util/iov.c
> > +++ b/util/iov.c
> > @@ -146,7 +146,7 @@ ssize_t iov_send_recv(int sockfd, struct iovec *iov, 
> > unsigned iov_cnt,
> >   {
> >       ssize_t total = 0;
> >       ssize_t ret;
> > -    size_t orig_len, tail;
> > +    size_t orig_len = 0, tail;
> >       unsigned niov;
> >
> >       while (bytes > 0) {
>
> Here are the uses of orig_len:
>
>          if (tail) {
>              /* second, fixup the last element, and remember the original
>               * length */
>              assert(niov < iov_cnt);
>              assert(iov[niov].iov_len > tail);
>              orig_len = iov[niov].iov_len;
>              iov[niov++].iov_len = tail;
>          }
>
>          ret = do_send_recv(sockfd, iov, niov, do_send);
>
>          /* Undo the changes above before checking for errors */
>          if (tail) {
>              iov[niov-1].iov_len = orig_len;
>          }
>
>
> gcc is too stupid to understand the control flow.  The initialization
> shuts it up.
>
> Personally, I dislike "shut up" initializations, because when you
> mistakenly adds a new uninitialized use, you get the arbitrary "shut up"
> value without warning.
>
> Possible alternative:
>
>          if (tail) {
>              /* second, fixup the last element, and remember the original
>               * length */
>              assert(niov < iov_cnt);
>              assert(iov[niov].iov_len > tail);
>              orig_len = iov[niov].iov_len;
>              iov[niov++].iov_len = tail;
>              ret = do_send_recv(sockfd, iov, niov, do_send);
>              /* Undo the changes above before checking for errors */
>              iov[niov-1].iov_len = orig_len;
>          } else {
>              ret = do_send_recv(sockfd, iov, niov, do_send);
>          }
  OK to work, but duplicated a line. I think it is not bad to give
default value as zero, even there will be new use later.

--
Best Regards

Wenchao Xia