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Fix aliasing bug causing in_cksum() to fail on odd packet sizes

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due to compiler optimization.

PR:		bin/13292
Suggested by:	wollman
This commit is contained in:
Pierre Beyssac 1999-11-15 20:04:53 +00:00
parent 309c48c65b
commit 3ec12efecc
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=53191
1 changed files with 9 additions and 5 deletions
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14
sbin/ping/ping.c
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@ -929,7 +929,10 @@ in_cksum(addr, len)
register int nleft = len; register int nleft = len;
register u_short *w = addr; register u_short *w = addr;
register int sum = 0; register int sum = 0;
u_short answer = 0; union {
u_int16_t us;
u_int8_t uc[2];
} answer;
/* /*
* Our algorithm is simple, using a 32 bit accumulator (sum), we add * Our algorithm is simple, using a 32 bit accumulator (sum), we add
@ -943,15 +946,16 @@ in_cksum(addr, len)
/* mop up an odd byte, if necessary */ /* mop up an odd byte, if necessary */
if (nleft == 1) { if (nleft == 1) {
*(u_char *)(&answer) = *(u_char *)w ; answer.uc[0] = *(u_char *)w;
sum += answer; answer.uc[1] = 0;
sum += answer.us;
} }
/* add back carry outs from top 16 bits to low 16 bits */ /* add back carry outs from top 16 bits to low 16 bits */
sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */ sum = (sum >> 16) + (sum & 0xffff); /* add hi 16 to low 16 */
sum += (sum >> 16); /* add carry */ sum += (sum >> 16); /* add carry */
answer = ~sum; /* truncate to 16 bits */ answer.us = ~sum; /* truncate to 16 bits */
return(answer); return(answer.us);
} }
/* /*