net: Use packed structures for networking

PXE boot is broken with GCC 7.1 due option '-fstore-merging' enabled
by default for '-O2':

BOOTP broadcast 1
data abort
pc : [<8ff8bb30>]          lr : [<00004f1f>]
reloc pc : [<17832b30>]    lr : [<878abf1f>]
sp : 8f558bc0  ip : 00000000     fp : 8ffef5a4
r10: 8ffed248  r9 : 8f558ee0     r8 : 8ffef594
r7 : 0000000e  r6 : 8ffed700     r5 : 00000000  r4 : 8ffed74e
r3 : 00060101  r2 : 8ffed230     r1 : 8ffed706  r0 : 00000ddd
Flags: nzcv  IRQs off  FIQs off  Mode SVC_32
Resetting CPU ...

Core reason is usage of structures for network headers without packed
attribute.

Reviewed-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/net/dns.h b/net/dns.h
index c4e96af..c55a5c1 100644
--- a/net/dns.h
+++ b/net/dns.h
@@ -29,7 +29,7 @@ struct header {
 	uint16_t	nauth;		/* Authority PRs */
 	uint16_t	nother;		/* Other PRs */
 	unsigned char	data[1];	/* Data, variable length */
-};
+} __attribute__((packed));
 
 void dns_start(void);		/* Begin DNS */