From 9d0b59f84e1170b12a128cdcccab5711f25b5dd8 Mon Sep 17 00:00:00 2001 From: Andy Green Date: Tue, 22 May 2018 09:24:42 +0800 Subject: [PATCH] mbuf: avoid integer promotion in prepend/adj/chain GCC 8.1 warned: In function 'rte_pktmbuf_prepend': rte_mbuf.h:1908:17: warning: conversion from 'int' to 'uint16_t' {aka 'short unsigned int'} may change value [-Wconversion] m->data_off -= len; ^~~ m->data_off is a uint16_t uint16_t data_off; len (a uint16_t) is promoted to an int using -=. Do the subtraction explicitly and cast the result to uint16_t. The below += or -= changes are solving the same thing. In function 'rte_pktmbuf_adj': rte_mbuf.h:1969:17: warning: conversion from 'int' to 'uint16_t' {aka 'short unsigned int'} may change value [-Wconversion] m->data_off += len; ^~~ In function 'rte_pktmbuf_chain': rte_mbuf.h:2082:19: warning: conversion from 'int' to 'uint16_t' {aka 'short unsigned int'} may change value [-Wconversion] head->nb_segs += tail->nb_segs; ^~~~ Also uint16_t uint16_t nb_segs; /**< Number of segments. */ Fixes: 08b563ffb19d ("mbuf: replace data pointer by an offset") Fixes: 1a60a0daa6e4 ("mbuf: fix segments number type increase") Cc: stable@dpdk.org Signed-off-by: Andy Green Acked-by: Bruce Richardson --- lib/librte_mbuf/rte_mbuf.h | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h index 0e89a69270..e136d12b74 100644 --- a/lib/librte_mbuf/rte_mbuf.h +++ b/lib/librte_mbuf/rte_mbuf.h @@ -1908,7 +1908,10 @@ static inline char *rte_pktmbuf_prepend(struct rte_mbuf *m, if (unlikely(len > rte_pktmbuf_headroom(m))) return NULL; - m->data_off -= len; + /* NB: elaborating the subtraction like this instead of using + * -= allows us to ensure the result type is uint16_t + * avoiding compiler warnings on gcc 8.1 at least */ + m->data_off = (uint16_t)(m->data_off - len); m->data_len = (uint16_t)(m->data_len + len); m->pkt_len = (m->pkt_len + len); @@ -1968,8 +1971,11 @@ static inline char *rte_pktmbuf_adj(struct rte_mbuf *m, uint16_t len) if (unlikely(len > m->data_len)) return NULL; + /* NB: elaborating the addition like this instead of using + * += allows us to ensure the result type is uint16_t + * avoiding compiler warnings on gcc 8.1 at least */ m->data_len = (uint16_t)(m->data_len - len); - m->data_off += len; + m->data_off = (uint16_t)(m->data_off + len); m->pkt_len = (m->pkt_len - len); return (char *)m->buf_addr + m->data_off; } @@ -2081,8 +2087,11 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail cur_tail = rte_pktmbuf_lastseg(head); cur_tail->next = tail; - /* accumulate number of segments and total length. */ - head->nb_segs += tail->nb_segs; + /* accumulate number of segments and total length. + * NB: elaborating the addition like this instead of using + * -= allows us to ensure the result type is uint16_t + * avoiding compiler warnings on gcc 8.1 at least */ + head->nb_segs = (uint16_t)(head->nb_segs + tail->nb_segs); head->pkt_len += tail->pkt_len; /* pkt_len is only set in the head */ -- 2.20.1