strange gdb behavior

[Max N. Boyarov-2]

Hi,

Who could help understand this:

`--> cat 1.c
int
main(int argc, char **argv)
{
        return 0;
}


`--> cc -ggdb -o 1 1.c


`--> gdb 1
GNU gdb 6.1.1 [FreeBSD]
Copyright 2004 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-marcel-freebsd"...
(gdb) set args test
(gdb) b main
Breakpoint 1 at 0x80483d0: file 1.c, line 3.
(gdb) r
Starting program: /tmp/1 test

Breakpoint 1, main () at 1.c:3
3       {
(gdb) print argc
Error accessing memory address 0x0: Bad address.
(gdb) list
1       int
2       main(int argc, char **argv)
3       {
4               return 0;
5       }

checked on 9.0-CURRENT, 8.0-BETA3

--
// Max N. Boyarov
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[Alexey Shuvaev-2]

On Mon, Nov 02, 2009 at 03:52:33PM +0200, Max Boyarov wrote:

> Hi,
>
> Who could help understand this:
>
> `--> cat 1.c
> int
> main(int argc, char **argv)
> {
>         return 0;
> }
>
> [snip]
>
> (gdb) set args test
> (gdb) b main
> Breakpoint 1 at 0x80483d0: file 1.c, line 3.
> (gdb) r
> Starting program: /tmp/1 test
>
> Breakpoint 1, main () at 1.c:3
> 3       {
> (gdb) print argc
> Error accessing memory address 0x0: Bad address.
> (gdb) list
> 1       int
> 2       main(int argc, char **argv)
> 3       {
> 4               return 0;
> 5       }
>
> checked on 9.0-CURRENT, 8.0-BETA3
>

On
FreeBSD wep4035 9.0-CURRENT FreeBSD 9.0-CURRENT #0 r198671: Fri Oct 30 16:12:10 CET 2009     root@wep4035:/usr/obj/usr/src/sys/GENERIC  amd64
I have the following:

(gdb) set args test
(gdb) b main
Breakpoint 1 at 0x40052b: file 1.c, line 4.
(gdb) r
Starting program: /home/lexx/1 test

Breakpoint 1, main (argc=2, argv=0x7fffffffe790) at 1.c:4
4               return 0;
(gdb) list
1       int
2       main(int argc, char **argv)
3       {
4               return 0;
5       }
(gdb) print argc
$1 = 2
(gdb)

Note that the breakpoint is set to line 4, not line 3 as in your case.
There was a series of changes to the linker recently. Update to the latest
CURRENT might help.

HTH,
Alexey.
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[Kostik Belousov]

On Mon, Nov 02, 2009 at 03:52:33PM +0200, Max Boyarov wrote:

> Hi,
>
> Who could help understand this:
>
> `--> cat 1.c
> int
> main(int argc, char **argv)
> {
>         return 0;
> }
>
>
> `--> cc -ggdb -o 1 1.c
>
>
> `--> gdb 1
> GNU gdb 6.1.1 [FreeBSD]
> Copyright 2004 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-marcel-freebsd"...
> (gdb) set args test
> (gdb) b main
> Breakpoint 1 at 0x80483d0: file 1.c, line 3.
> (gdb) r
> Starting program: /tmp/1 test
>
> Breakpoint 1, main () at 1.c:3
> 3       {
> (gdb) print argc
> Error accessing memory address 0x0: Bad address.
> (gdb) list
> 1       int
> 2       main(int argc, char **argv)
> 3       {
> 4               return 0;
> 5       }
>
> checked on 9.0-CURRENT, 8.0-BETA3

Can you check it on RELENG_7 ? It seems to be another old gdb bug.
With gdb 7.0,
(gdb) b main
Breakpoint 1 at 0x8048414: file hello.c, line 8.
(gdb) r
Starting program: /usr/home/kostik/build/bsd/6/stuff/hello1

Breakpoint 1, main (argc=1, argv=0xbfbfe53c) at hello.c:8
8               for (i = 0; i < argc; i++)

while in-tree gdb shows me the same behaviour as yours.

[Max N. Boyarov-2]

Kostik Belousov <kostikbel@...> writes:

> On Mon, Nov 02, 2009 at 03:52:33PM +0200, Max Boyarov wrote:
>> Hi,
[cut]

>
> Can you check it on RELENG_7 ? It seems to be another old gdb bug.
> With gdb 7.0,
> (gdb) b main
> Breakpoint 1 at 0x8048414: file hello.c, line 8.
> (gdb) r
> Starting program: /usr/home/kostik/build/bsd/6/stuff/hello1
>
> Breakpoint 1, main (argc=1, argv=0xbfbfe53c) at hello.c:8
> 8               for (i = 0; i < argc; i++)
>
> while in-tree gdb shows me the same behaviour as yours.

$ cat gdbt.c
#include <unistd.h>

int
main(int argc, char **argv)
{
        int t;

        t = getopt(argc, argv, "f:");

        return t;
}


$ cat gdbt.gdb
b main
run
print &argc
next
print &argc
list
quit


$ cat gdbt.sh
#!/bin/sh

uname -mr

cc -O0 -ggdb -o gdbt gdbt.c && gdb -nx -quiet -x gdbt.gdb gdbt


9.0-CURRENT i386 / r198846
Breakpoint 1 at 0x80483f0: file gdbt.c, line 5.

Breakpoint 1, main (argc=Error accessing memory address 0x2: Bad address.
) at gdbt.c:5
5       {
$1 = (int *) 0x2
main (argc=1, argv=0xbfbfe7e0) at gdbt.c:8
8               t = getopt(argc, argv, "f:");
$2 = (int *) 0xbfbfe7c0
3       int
4       main(int argc, char **argv)
5       {
6               int t;
7      
8               t = getopt(argc, argv, "f:");
9      
10              return t;
11      }


9.0-CURRENT amd64 /r198480
Breakpoint 1 at 0x40057f: file gdbt.c, line 8.

Breakpoint 1, main (argc=1, argv=0x7fffffffeac0) at gdbt.c:8
8               t = getopt(argc, argv, "f:");
$1 = (int *) 0x7fffffffea5c
10              return t;
$2 = (int *) 0x7fffffffea5c
5       {
6               int t;
7
8               t = getopt(argc, argv, "f:");
9
10              return t;
11      }


7.2-RELEASE-p1 i386
Breakpoint 1 at 0x8048400: file gdbt.c, line 5.

Breakpoint 1, main (argc=Error accessing memory address 0x2: Bad address.
) at gdbt.c:5
5       {
$1 = (int *) 0x2
main (argc=1, argv=0xbfbfeca4) at gdbt.c:8
8               t = getopt(argc, argv, "f:");
$2 = (int *) 0xbfbfec80
3       int
4       main(int argc, char **argv)
5       {
6               int t;
7
8               t = getopt(argc, argv, "f:");
9
10              return t;
11      }

7.2-RELEASE-p4 amd64
Breakpoint 1 at 0x40057f: file gdbt.c, line 8.

Breakpoint 1, main (argc=1, argv=0x7fffffffebc8) at gdbt.c:8
8               t = getopt(argc, argv, "f:");
$1 = (int *) 0x7fffffffeb5c
10              return t;
$2 = (int *) 0x7fffffffeb5c
5       {
6               int t;
7
8               t = getopt(argc, argv, "f:");
9
10              return t;
11      }


--
Max N. Boyarov
xmpp:zotrix@...
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[Dag-Erling Smørgrav]

m.boyarov@... (Max N. Boyarov) writes:
> 9.0-CURRENT i386 / r198846
> [broken]
> 9.0-CURRENT amd64 /r198480
> [works]
> 7.2-RELEASE-p1 i386
> [broken]
> 7.2-RELEASE-p4 amd64
> [works]

See a pattern?

DES
--
Dag-Erling Smørgrav - des@...
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