Date: Fri, 21 Jul 2000 17:37:51 -0400 From: System Administrator <admin@chemcomp.com> To: Rahul Siddharthan <rsidd@physics.iisc.ernet.in> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Tar bug??? Message-ID: <3978C2AF.7A6362D4@chemcomp.com> References: <3978A6F6.55C3E578@chemcomp.com> <20000722021522.A8449@physics.iisc.ernet.in>
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Rahul Siddharthan wrote:
>
> System Administrator said on Jul 21, 2000 at 15:39:34:
> >
> > I was about to submit a PR when a doubt crossed my mind. Is this a bug
> > or a "feature"?
> >
> > $ tar -f /home/backup/arch.tar -A -v -C /net /net/basil
> > tar: Segmentation fault
> > $
> >
> > Curiously, no core is dumped, so I cannot really debug (?) the problem.
> > How could I? Why isn't there a core anyways?
>
> It would dump core only if it has write permission in the current
> working directory. Try running the same command from your
> home directory, if you aren't doing that already.
Ah! That's better...
> Looks like a bug to me.
Indeed.
(gdb) bt
#0 0x8073976 in vfprintf ()
#1 0x80729c4 in fprintf ()
#2 0x8072cb0 in vfprintf ()
#3 0x8052292 in msg_perror (
str=0x80825c0 "read error at byte %ld reading %d bytes in file %s")
at port.c:1138
#4 0x8054845 in append_file (p=0x8092095 "/net/basil") at update.c:228
#5 0x8054724 in update_archive () at update.c:182
#6 0x8052b11 in main (argc=8, argv=0xbfbffc18) at tar.c:231
#7 0x80480f9 in _start ()
(gdb)
I can trace back the problem to the call:
228 msg_perror ("read error at byte %ld reading %d bytes in file %s",
statbuf.st_size - bytes_left, bufsiz, p);
(gdb) p statbuf.st_size - bytes_left
$5 = 0
(gdb) p p
$6 = 0x8092095 "/net/basil"
(gdb) p bufsiz
$7 = 1024
The problem seems to be that when msg_perror is called with a 0 (zero)
arg, it crashes. Now the problem is that va_arg() is completely out of
my range.. :)
In fact, the real faulty line is:
#3 0x8052292 in msg_perror (
str=0x80825c0 "read error at byte %ld reading %d bytes in file %s")
at port.c:1138
vfprintf (stderr, str, args);
But I can't just display the value of args and I really don't understand
(and never did) the whole va_arg() working principles.
(gdb) print args
No symbol "args" in current context.
(gdb)
ARG(H)!
Can someone help me out with this so I can send a PR and get this over
with? :))
Something very strange is that it crashes only when accessing
'automounted' directories:
bash-2.03$ ./tar -f /dev/null -A -v -C . /tmp
bash-2.03$ ./tar -f /dev/null -A -v -C . /
bash-2.03$ ./tar -f /dev/null -A -v -C . /net/basil/u
./tar: Segmentation fault (core dumped)
bash-2.03$ ./tar -f /dev/null -A -v -C . /net/basil/u/jocelyn
./tar: Segmentation fault (core dumped)
bash-2.03$ ./tar -f /dev/null -A -v -C . /usr/tmp
bash-2.03$ ./tar -f /dev/null -A -v -C . /usr/local/bin
bash-2.03$ ./tar -f /dev/null -A -v -C . /net/sky/usr/home
./tar: Segmentation fault (core dumped)
bash-2.03$
And also, it does not crash with the -c function:
bash-2.03$ ./tar -f /dev/null -c -v -C . /net/sky/usr/home
./tar: Removing leading / from absolute path names in the archive.
net/sky/usr/home/
[...]
Weird. But thanks a lot for the core dump hint! I'll remember...
--
Antoine Beaupre
System Administrator
Chemical Computing Group, Inc.
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