RE: unknowns "??" while debugging executable created for target i686-pc-linux-gnu

[vijay nag <vijunag at gmail dot com>]

Hello,

I recently upgraded the compiler from gcc-3.3.6(i386) to
gcc-4.7.2(i686) to my project. gdb is having trouble printing the
back-trace when debugging is stopped by "ctrl + c".
I'm using gdb-7.5 configured for i686 target to debug my executable
~/vinag/gdb/bin/gdb -v
GNU gdb (GDB) 7.5
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-pc-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.


Program received signal SIGINT, Interrupt.
0xb7fff410 in ?? ()
(gdb) bt
#0  0xb7fff410 in ?? ()
Cannot access memory at address 0x51
(gdb) info registers
eax            0xfffffffc	-4
ecx            0x22	34
edx            0x5	5
ebx            0x1e8e8c88	512658568
esp            0xbffff2a8	0xbffff2a8
ebp            0x4d	0x4d
esi            0x5	5
edi            0x0	0
eip            0xb7fff410	0xb7fff410
eflags         0x246	[ PF ZF IF ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x33	51
(gdb)

Looks like frame-pointer $ebp  is containing junk values and I don't
understand why it is containing junk values. However if I insert a
break-point at a location, gdb is somehow able to decode
the call stack.
Breakpoint 1, sn_assert_init (argc=5, argv=0xbffff844,
stackbot=stackbot@entry=0xbffff7c8, domain=7, procldatafunc=0x13087852
<sn_assert_fill_proclet_data>,
    callgen=callgen@entry=0,
minicore_dir_suffix=minicore_dir_suffix@entry=0x0) at
snutil/sn_assert_handler.c:823
823	{
(gdb) bt
#0  assert_init (argc=5, argv=0xbffff844,
stackbot=stackbot@entry=0xbffff7c8, domain=7)..assert_handler.c:823
#1  0x12eedcec in main (argc=5, argv=0xbffff844, env=0xbffff85c) at main.c:256
(gdb) f 0
#0  assert_init (argc=5, argv=0xbffff844,
stackbot=stackbot@entry=0xbffff7c8, domain=7)...assert_handler.c:823
823	{
(gdb) info registers
eax            0x5	5
ecx            0x0	0
edx            0xbffffe32	-1073742286
ebx            0x1eb62400	515253248
esp            0xbffff75c	0xbffff75c
ebp            0xbffff7b8	0xbffff7b8
esi            0x0	0
edi            0x18f63d48	418790728
eip            0x1308abff	0x1308abff <assert_init>
eflags         0x286	[ PF SF IF ]
cs             0x73	115
ss             0x7b	123
ds             0x7b	123
es             0x7b	123
fs             0x0	0
gs             0x33	51
(gdb) p *(0xbffff7b8 + 4)
$1 = 343195968
(gdb) info line *343195968
Line 292 of "libc-start.c" starts at address 0x1474c140
<__libc_start_main+464> and ends at 0x1474c148
<__libc_start_main+472>.
(gdb)

What could be the issue here ?