From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Mon, 3 Dec 2018 16:50:03 +0300 From: Vladimir Davydov Subject: Re: [PATCH 04/11] sio: fix passing negative size_t to sio_add_to_iov Message-ID: <20181203135003.beibxo7vwnwiam2m@esperanza> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: To: Vladislav Shpilevoy Cc: tarantool-patches@freelists.org List-ID: On Fri, Nov 30, 2018 at 06:39:36PM +0300, Vladislav Shpilevoy wrote: > sio_add_to_iov moves struct iov position on a > specified offset, positive or negative. But its offset > argument has size_t type, which is unsigned. Make it > be ssize_t. > > This worked before thanks to how negative numbers are > stored. For example, consider > > uint8_t value = 100; > uint8_t offset = -5; > > Value is stored as 0110 0100. > Offset is stored as 1111 1011. (Yes, 1011, not 1010). > > Sum of the values above is 0001 0101 1111 - first quad > overflows and is truncated, so the result is > 0101 1111 = 95 - correct. > --- > src/sio.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/src/sio.h b/src/sio.h > index ab0a243cd..ff383aa36 100644 > --- a/src/sio.h > +++ b/src/sio.h > @@ -84,7 +84,7 @@ sio_move_iov(struct iovec *iov, size_t nwr, size_t *iov_len) > * to adjust to a partial write. > */ > static inline void > -sio_add_to_iov(struct iovec *iov, size_t size) > +sio_add_to_iov(struct iovec *iov, ssize_t size) > { > iov->iov_len += size; 'iov_len' has type size_t so 'size' will be converted to size_t before the operation, in other words this patch has, in fact, no effect. Anyway, it's OK to apply unary minus to an unsigned variable: no matter how integer types are stored, whether the machine uses two's-complement or not, it should work so that (-x + x) equals 0. That being said, I don't think we need this patch.