Date: Tue, 13 Jun 2000 12:23:01 -0400 (EDT) From: Mikhail Teterin <mi@privatelabs.com> To: FreeBSD-gnats-submit@freebsd.org Subject: i386/19245: -fexpensive-optimizations buggy (even with -O) Message-ID: <200006131623.MAA61270@misha.privatelabs.com>
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>Number: 19245
>Category: i386
>Synopsis: -fexpensive-optimizations buggy (even with -O)
>Confidential: no
>Severity: serious
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Tue Jun 13 09:30:00 PDT 2000
>Closed-Date:
>Last-Modified:
>Originator: Mikhail Teterin
>Release: FreeBSD 4.0-STABLE i386
>Organization:
Virtual Estates, Inc.
>Environment:
CPU: Pentium II/Pentium II Xeon/Celeron (334.09-MHz 686-class CPU)
Pentium Pro MTRR support enabled
>Description:
The attached piece of code, when compiled with
``-O -fexpensive-optimizations'', produces incorrect
binary on FreeBSD-4.0 .
I tested the same compiler line on Mandrake Linux (an
identical machine hardware-wise) and it compiles correctly.
Mandrake's cc is the same as on FreeBSD:
Reading specs from
/usr/lib/gcc-lib/i586-mandrake-linux/2.95.2/specs
gcc version 2.95.2 19991024 (release)
vs. our
Using builtin specs.
gcc version 2.95.2 19991024 (release)
But their assembler is newer:
GNU assembler version 2.9.5 (i686-pc-linux-gnu)
using BFD version 2.9.5.0.16
vs. our
GNU assembler version 2.9.1 (i386-unknown-freebsdelf),
using BFD version 2.9.1
>How-To-Repeat:
Save the C-code below into a file bug.c. Then compile it with
cc -O -fexpensive-optimizations bug.c -o bug
As you can see from the code, the hostname output by both
printfs shoud be the same, and on Linux and on FreeBSD without
the -fexpensive-optimizations flag it is:
Calling rfc1035QuestionPack with hostname 0xbffffe32 (./bug)
In rfc1035QuestionPack: hostname is 0xbffffe32 (./bug)
Yet, with the -fexpensive-optimizations flag, the hostname
argument is passed in the register, which, apparently, is
sometimes not loaded with the value and remains zero, resulting
in:
Calling rfc1035QuestionPack with hostname 0xbfbff8f0 (./bug)
In rfc1035QuestionPack: hostname is 0x0 ((null))
The code is stripped from the squid23's lib/rfc1035.c (I found
this because squid was crashing on every request and restarting)
-- I tried to reduce it to the bare minimum needed to reproduce
the bug.
/* beginning of end.c */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <assert.h>
#include <strings.h>
static off_t
rfc1035QuestionPack(char *buf,
size_t sz,
const char *hostname,
unsigned short class
)
{
off_t off = 0;
unsigned short s;
printf("In rfc1035QuestionPack: hostname is %p (%s)\n",
hostname, hostname);
s = htons(class);
memcpy(buf + off, &s, sizeof(s));
off += sizeof(s);
assert(off <= sz);
return off;
}
static unsigned short
rfc1035BuildAQuery(const char *hostname, char *buf, size_t sz)
{
off_t offset = 0;
printf("Calling rfc1035QuestionPack with hostname %p (%s)\n",
hostname, hostname);
offset += rfc1035QuestionPack(buf + offset,
sz - offset,
hostname,
1
);
return 0;
}
int main(int argc, char *argv[]) {
char buf[1024];
rfc1035BuildAQuery(argv[argc - 1], buf, 1024);
return 0;
}
/* end of bug.c */
>Fix:
Get the new assembler/binutils and add -fno-expensive-optimizations
to all CFLAGS in the meantime. Anything else?
>Release-Note:
>Audit-Trail:
>Unformatted:
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