GDB Core dump: Recover argc argv values after crash - c++

Question

Is possible to recover the exact values of argv and argc parameters of a main after the application crashed?
I need to use only the application core-dump and gdb debugger on Linux.

Answer 1

Yes, if application was compiled with debug info. Open core dump in gdb and find frame containing main function. Then go to this frame and print values of argv and argc. Here is sample gdb session.
[root#localhost ~]# gdb ./a.out core.2020
GNU gdb (GDB) 7.2
Copyright (C) 2010 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/>...
Reading symbols from /root/a.out...done.
[New Thread 2020]
warning: Can't read pathname for load map: Input/output error.
Reading symbols from /usr/lib/libstdc++.so.6...(no debugging symbols found)...done.
Loaded symbols for /usr/lib/libstdc++.so.6
Reading symbols from /lib/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libm.so.6
Reading symbols from /lib/libgcc_s.so.1...(no debugging symbols found)...done.
Loaded symbols for /lib/libgcc_s.so.1
Reading symbols from /lib/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/libc.so.6
Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib/ld-linux.so.2
Core was generated by `./a.out'.
Program terminated with signal 6, Aborted.
#0 0x0027b424 in __kernel_vsyscall ()
(gdb) bt
#0 0x0027b424 in __kernel_vsyscall ()
#1 0x00b28b91 in raise () from /lib/libc.so.6
#2 0x00b2a46a in abort () from /lib/libc.so.6
#3 0x007d3397 in __gnu_cxx::__verbose_terminate_handler() () from /usr/lib/libstdc++.so.6
#4 0x007d1226 in ?? () from /usr/lib/libstdc++.so.6
#5 0x007d1263 in std::terminate() () from /usr/lib/libstdc++.so.6
#6 0x007d13a2 in __cxa_throw () from /usr/lib/libstdc++.so.6
#7 0x08048940 in main (argv=1, argc=0xbfcf1754) at test.cpp:14
(gdb) f 7
#7 0x08048940 in main (argv=1, argc=0xbfcf1754) at test.cpp:14
14 throw std::runtime_error("123");
(gdb) p argv
$1 = 1
(gdb) p argc
$2 = (char **) 0xbfcf1754
(gdb)

Answer 2

Looks like you need to start from the basics..!!
compiler your application code with -g flag, make sure you dont strip it.
Say if I wanted to compile hello.c
gcc -c -g hello.c -o hello.o
gcc hello.o -o hello
now if you dont want to debug
ulimit -c unlimited
./hello
when the application crashes a core file wiil be generated.
To examine the core file
"gdb ./hello core.$$$" this will list you your stack.
you can also choose to debug the image
gdb hello
There are a lot of stuffs over the internet about GDB, do go through them.