[dpdk-stable] patch 'mbuf: avoid integer promotion in prepend/adj/chain' has been queued to stable release 18.02.2

[luca.boccassi at gmail.com]

Hi,

FYI, your patch has been queued to stable release 18.02.2

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 05/25/18. So please
shout if anyone has objections.

Thanks.

Luca Boccassi

---
>From f622d2e35942e94e43746ef9f1fe64f4a0f54a4b Mon Sep 17 00:00:00 2001
From: Andy Green <andy at warmcat.com>
Date: Tue, 22 May 2018 09:24:42 +0800
Subject: [PATCH] mbuf: avoid integer promotion in prepend/adj/chain

[ upstream commit 9d0b59f84e1170b12a128cdcccab5711f25b5dd8 ]

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")

Signed-off-by: Andy Green <andy at warmcat.com>
Acked-by: Bruce Richardson <bruce.richardson at intel.com>
---
 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 38299992e..f247e43ca 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1686,7 +1686,10 @@ 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);
 
@@ -1746,8 +1749,11 @@ 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;
 }
@@ -1859,8 +1865,11 @@ 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 */
-- 
2.14.2