Date: 11 Dec 2000 17:29:16 -0000 From: Peter Pentchev <roam@orbitel.bg> To: FreeBSD-gnats-submit@freebsd.org Subject: bin/23472: gdb weirdness on programs compiled with -ggdb Message-ID: <20001211172916.4381.qmail@ringworld.nanolink.com> Resent-Message-ID: <200012111740.eBBHe1m40780@freefall.freebsd.org>
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>Number: 23472
>Category: bin
>Synopsis: gdb weirdness on programs compiled with -ggdb
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Dec 11 09:40:00 PST 2000
>Closed-Date:
>Last-Modified:
>Originator: Peter Pentchev
>Release: FreeBSD 4.2-STABLE i386
>Organization:
Orbitel JSCo.
>Environment:
FreeBSD FreeBSD 4.2-STABLE #6: Mon Dec 11 12:57:38 EET 2000 root@ringworld.oblivion.bg:/usr/obj/usr/src/sys/RINGWORLD
>Description:
If a program is compiled with -ggdb, gdb sometimes loses track of local
variables' addresses and/or contents.
>How-To-Repeat:
Consider the following program:
#include <stdio.h>
#include <unistd.h>
#define BUFLEN 100
int
readstring(char *s, int len) {
printf("readstring(%p, %d) called, s='%s'\n", s, len, s);
return 0;
}
int
main(void) {
char str[BUFLEN] = "string";
printf("in main: str=%p, sizeof(str)=%d, str='%s'\n", str, sizeof(str), str);
readstring(str, sizeof(str));
return 0;
}
..and the following Makefile:
CFLAGS = -g3 -ggdb
all: zettest
clean:
rm -f zettest
Following is the transcript of a gdb session.
Script started on Mon Dec 11 17:48:52 2000
[roam@ringwraith ~/c/misc/zettest]$ gdb zettest
GNU gdb 4.18
Copyright 1998 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB. Type "show warranty" for details.
This GDB was configured as "i386-unknown-freebsd"...
(gdb) br main
Breakpoint 1 at 0x8048572: file zettest.c, line 15.
(gdb) r
Starting program: /usr/home/roam/lang/c/misc/zettest/zettest
Breakpoint 1, main () at zettest.c:15
15 char str[BUFLEN] = "string";
(gdb) n
17 printf("in main: str=%p, sizeof(str)=%d, str='%s'\n", str, sizeof(str), str);
(gdb)
in main: str=0xbfbff904, sizeof(str)=100, str='string'
^^^^^^^^^^ real address ^^^^^^^^ real contents
18 readstring(str, sizeof(str));
(gdb) print (void *) str
$1 = (void *) 0xbfbff88c
^^^^^^^^^^ something's fishy..
(gdb) print &str[0]
$2 = 0xbfbff88c ""
(gdb) s
readstring (s=0xbfbff968 "´ù¿¿\211\204\004\b\001", len=134514114)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ uhm ^^^^^^^^^ excuse me?!
at zettest.c:9
9 printf("readstring(%p, %d) called, s='%s'\n", s, len, s);
(gdb) n
readstring(0xbfbff904, 100) called, s='string'
^^^^^^^^^^ ^^^ ^^^^^^ everyhing's just fine
10 return 0;
(gdb) c
Continuing.
Program exited normally.
(gdb) quit
[roam@ringwraith ~/c/misc/zettest]$ exit
exit
Script done on Mon Dec 11 17:49:15 2000
Well, so.. the program executed correctly, the addresses and values
as printed by the printf() in readstring() were perfectly OK. Just gdb
showed something wrong - in a program compiled with additional info
for the purpose of debugging with gdb :)
Here's the 'ident gdb' output..
/usr/bin/gdb:
$FreeBSD: src/lib/libc/i386/string/strrchr.S,v 1.5 1999/08/27 23:59:35 peter Exp $
$FreeBSD: src/lib/libc/i386/string/strncmp.S,v 1.6 1999/08/27 23:59:35 peter Exp $
$FreeBSD: src/lib/libc/i386/string/index.S,v 1.5 1999/08/27 23:59:30 peter Exp $
$FreeBSD: src/lib/libc/i386/string/strcpy.S,v 1.5 1999/08/27 23:59:34 peter Exp $
$FreeBSD: src/lib/libc/i386/string/strcmp.S,v 1.5 1999/08/27 23:59:33 peter Exp $
$FreeBSD: src/lib/libc/i386/string/memchr.S,v 1.8 1999/08/27 23:59:31 peter Exp $
$NetBSD: bcopy.S,v 1.6 1996/11/12 00:50:06 jtc Exp $
$FreeBSD: src/lib/libc/i386/string/memset.S,v 1.5 1999/08/27 23:59:32 peter Exp $
$NetBSD: bcopy.S,v 1.6 1996/11/12 00:50:06 jtc Exp $
$FreeBSD: src/lib/libc/i386/sys/brk.S,v 1.7 1999/08/27 23:59:38 peter Exp $
$FreeBSD: src/lib/libc/i386/sys/sbrk.S,v 1.7 1999/08/27 23:59:44 peter Exp $
$FreeBSD: src/lib/libc/i386/sys/cerror.S,v 1.10 1999/08/27 23:59:38 peter Exp $
$FreeBSD: src/lib/libc/gen/err.c,v 1.6 1999/08/27 23:58:33 peter Exp $
$FreeBSD: src/lib/libc/i386/gen/isinf.c,v 1.6 1999/08/27 23:59:21 peter Exp $
$FreeBSD: src/lib/libc/stdio/asprintf.c,v 1.6 1999/08/28 00:00:55 peter Exp $
I do not know which FreeBSD releases are affected by this - I only have
very recent 4.2-STABLE and -current machines :( And freefall was updated
to a very-very recent 4.2-STABLE just hours before I needed to test :)
>Fix:
Wish I knew :( A friend wasted hours today in a gdb session, thinking
his program was passing a value of 100 as 134 millions.. and at the same
time marvelling at the program's perfectly fine output :(
>Release-Note:
>Audit-Trail:
>Unformatted:
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