[dpdk-stable] patch 'mbuf: avoid integer promotion in prepend/adj/chain' has been queued to LTS release 17.11.5

[Yongseok Koh <yskoh@mellanox.com>]

Hi,

FYI, your patch has been queued to LTS release 17.11.5

Note it hasn't been pushed to http://dpdk.org/browse/dpdk-stable yet.
It will be pushed if I get no objections before 01/04/19. So please
shout if anyone has objections.

Also note that after the patch there's a diff of the upstream commit vs the patch applied
to the branch. If the code is different (ie: not only metadata diffs), due for example to
a change in context or macro names, please double check it.

Thanks.

Yongseok

---
>From 91f14efa3ea358957b7292d406fe1cf3627b4c78 Mon Sep 17 00:00:00 2001
From: Andy Green <andy@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@warmcat.com>
Acked-by: Bruce Richardson <bruce.richardson@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 8c63a9fdb..e6fd86f29 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1666,7 +1666,10 @@ 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);
 
@@ -1726,8 +1729,11 @@ 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;
 }
@@ -1839,8 +1845,11 @@ 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 */
-- 
2.11.0

---
  Diff of the applied patch vs upstream commit (please double-check if non-empty:
---
--- -	2019-01-02 23:59:13.975320321 -0800
+++ 0036-mbuf-avoid-integer-promotion-in-prepend-adj-chain.patch	2019-01-02 23:59:12.105818000 -0800
@@ -1,8 +1,10 @@
-From 9d0b59f84e1170b12a128cdcccab5711f25b5dd8 Mon Sep 17 00:00:00 2001
+From 91f14efa3ea358957b7292d406fe1cf3627b4c78 Mon Sep 17 00:00:00 2001
 From: Andy Green <andy@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':
@@ -36,7 +38,6 @@
 
 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 <andy@warmcat.com>
 Acked-by: Bruce Richardson <bruce.richardson@intel.com>
@@ -45,10 +46,10 @@
  1 file changed, 13 insertions(+), 4 deletions(-)
 
 diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
-index 0e89a6927..e136d12b7 100644
+index 8c63a9fdb..e6fd86f29 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,
+@@ -1666,7 +1666,10 @@ static inline char *rte_pktmbuf_prepend(struct rte_mbuf *m,
  	if (unlikely(len > rte_pktmbuf_headroom(m)))
  		return NULL;
  
@@ -60,7 +61,7 @@
  	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)
+@@ -1726,8 +1729,11 @@ static inline char *rte_pktmbuf_adj(struct rte_mbuf *m, uint16_t len)
  	if (unlikely(len > m->data_len))
  		return NULL;
  
@@ -73,7 +74,7 @@
  	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
+@@ -1839,8 +1845,11 @@ static inline int rte_pktmbuf_chain(struct rte_mbuf *head, struct rte_mbuf *tail
  	cur_tail = rte_pktmbuf_lastseg(head);
  	cur_tail->next = tail;