From: Michael Qiu <michael.qiu@intel.com>
Date: Thu, 4 Dec 2014 04:16:04 +0000 (+0800)
Subject: net: fix build with gcc 4.4.7 and strict aliasing
X-Git-Tag: spdx-start~9961
X-Git-Url: http://git.droids-corp.org/?a=commitdiff_plain;h=2b039d5f20a3;hp=42c035e7bbfe95f26ee4ddf2559b94f574974a86;p=dpdk.git

net: fix build with gcc 4.4.7 and strict aliasing

include/rte_ip.h:161: error: dereferencing pointer ‘u16’
        does break strict-aliasing rules
include/rte_ip.h:157: note: initialized from here
        ...

The root cause is that, compile enable strict aliasing by default,
while in function rte_raw_cksum() try to convert 'const char *'
to 'const uint16_t *'.

This workaround is to solve the compile issue of GCC strict-aliasing (two
different type pointers should not be point to the same memory address).

For GCC 4.4.7 it will definitely occurs if  flags "-fstrict-aliasing"
and "-Wall" used.

Signed-off-by: Michael Qiu <michael.qiu@intel.com>
[Thomas: add workaround comment]
Acked-by: Thomas Monjalon <thomas.monjalon@6wind.com>
---

diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
index 61e44579a3..46f049716a 100644
--- a/lib/librte_net/rte_ip.h
+++ b/lib/librte_net/rte_ip.h
@@ -154,7 +154,9 @@ struct ipv4_hdr {
 static inline uint16_t
 rte_raw_cksum(const char *buf, size_t len)
 {
-	const uint16_t *u16 = (const uint16_t *)buf;
+	/* workaround gcc strict-aliasing warning */
+	uintptr_t ptr = (uintptr_t)buf;
+	const uint16_t *u16 = (const uint16_t *)ptr;
 	uint32_t sum = 0;
 
 	while (len >= (sizeof(*u16) * 4)) {