egcs-1.1.2 breaks ping(1) on i386

[Jeffrey A Law]

  In message <199904120025.UAA01830@sleipnir.valparaiso.cl>you write:
  > ------- =_aaaaaaaaaa0
  > Content-Type: text/plain; charset="us-ascii"
  > Content-ID: <1823.923876521.1@sleipnir.valparaiso.cl>
  > 
  > The ping source from the widely deployed netkit-0.10 breaks when compiled
  > on ia32 with egcs-1.1.2. A testcase follows, with annotated .s file (buggy
  > asm pointed out by "Petr Vandrovec Ing. VTEI" <VANDROVE@vc.cvut.cz>).
  > 
  > ------- =_aaaaaaaaaa0
  > Content-Type: text/plain; name="tst.c"; charset="us-ascii"
  > Content-ID: <1823.923876521.2@sleipnir.valparaiso.cl>
  > Content-Description: Checksum routine from ping.c in netkit-0.10 source (ed
  > ited)
  > 
  > /*
  >  * in_cksum --
  >  *	Checksum routine for Internet Protocol family headers (C Version)
  >  */
  > static int
  > in_cksum(unsigned short *addr, int len)
  > {
  > 	register int nleft = len;
  > 	register unsigned short *w = addr;
  > 	register int sum = 0;
  > 	unsigned short answer = 0;
  > 
  > 	/*
  > 	 * Our algorithm is simple, using a 32 bit accumulator (sum), we add
  > 	 * sequential 16 bit words to it, and at the end, fold back all the
  > 	 * carry bits from the top 16 bits into the lower 16 bits.
  > 	 */
  > 	while (nleft > 1)  {
  > 		sum += *w++;
  > 		nleft -= 2;
  > 	}
  > 
  > 	/* mop up an odd byte, if necessary */
  > 	if (nleft == 1) {
  > 		*(unsigned char *)(&answer) = *(unsigned char *)w ;
  > 		sum += answer;
  > 	}
  > 
  > 	/* 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);			/* add carry */
  > 	answer = ~sum;				/* truncate to 16 bits */
  > 	return(answer);
  > }
I just checked this with the current sources and I'm pretty sure we generate
correct code with the gcc-2.95 CVS sources.


Jeff