Date: Sun, 6 Jun 1999 23:07:42 -0700 (PDT) From: Bryce Newall <data@dreamhaven.net> To: FreeBSD Questions List <freebsd-questions@freebsd.org> Cc: trv@dreamhaven.net Subject: Possible C library bug? Message-ID: <Pine.NEB.4.10.9906062301420.99176-100000@ds9.dreamhaven.net>
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Greetings!
One of my users recently brought to my attention a possible bug in either
the FreeBSD C compilers (cc and gcc), or one of the libraries. The bug
has to do with attempting to close a file that was never successfully
opened. In other words, with a statement something like:
f = fopen("filename", "r");
If the fopen fails, for whatever reason, and f has a value of NULL, then
this statement:
flose(f);
will return a segmentation fault, instead of simply not doing anything.
Here is a piece of code that he wrote to test it:
include <stdio.h>
/* Purpose: to test how fclose() handles NULL pointers.
*/
void main() {
int iStat;
FILE *fp;
char szLine[BUFSIZ];
fp = fopen("doesnotexist.file", "r");
if (!fp) {
iStat = fclose(fp);
} else {
fgets(szLine, BUFSIZ, fp);
iStat = fclose(fp);
}
}
I logged into his account, and performed the following tests: (The file
above is the one called testgcc.c)
trv@calico:/home/trv/src>% cc -o testcc testgcc.c
trv@calico:/home/trv/src>% gcc -o testgcc testgcc.c
trv@calico:/home/trv/src>% ./testcc
Segmentation fault (core dumped)
trv@calico:/home/trv/src>% ./testgcc
Segmentation fault (core dumped)
trv@calico:/home/trv/src>% uname -a
FreeBSD calico.dreamhaven.net 3.1-STABLE FreeBSD 3.1-STABLE #4: Thu May 13
16:50:23 MDT 1999
root@calico.dreamhaven.net:/usr/src/sys/compile/CALICO i386
As you can see, the program dumped core both with cc and gcc. I made the
same test on a Linux system:
bahamut:/root# cc -o testcc testgcc.c
bahamut:/root# gcc -o testgcc testgcc.c
bahamut:/root# ./testcc
bahamut:/root# ./testgcc
bahamut:/root# uname -a
Linux bahamut 2.0.35 #5 Sun Dec 13 08:57:24 EST 1998 i586
No problem there. Same thing with a Solaris machine, aside from a gcc
compiler warning:
[9]newall@rohan:/home/ma/t/newall % cc -o testcc testgcc.c
[10]newall@rohan:/home/ma/t/newall % gcc -o testgcc testgcc.c
testgcc.c: In function `main':
testgcc.c:6: warning: return type of `main' is not `int'
[11]newall@rohan:/home/ma/t/newall % ./testcc
[12]newall@rohan:/home/ma/t/newall % ./testgcc
[13]newall@rohan:/home/ma/t/newall % uname -a
SunOS rohan 5.6 Generic_105181-14 sun4u sparc SUNW,Ultra-Enterprise
Perhaps there's a compiler flag that is required under FreeBSD, but not
under these other OS's? Or do you think this may indeed be a bug?
Thanks for your time!
**********************************************************************
* Bryce Newall * Email: data@dreamhaven.net *
* WWW: http://www.dreamhaven.net/~data * ICQ: 32620929 *
* "Insanity takes its toll. Please have exact change." *
**********************************************************************
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