The address where filename has been loaded is missing [GDB] - linux

Question

I have following sample code
#include<stdio.h>
int main()
{
int num1, num2;
printf("Enter two numbers\n");
scanf("%d",&num1);
scanf("%d",&num2);
int i;
for(i = 0; i < num2; i++)
num1 = num1 + num1;
printf("Result is %d \n",num1);
return 0;
}
I compiled this code with -g option to gcc.
gcc -g file.c
Generate separate symbol file
objcopy --only-keep-debug a.out a.out.sym
Strip the symbols from a.out
strip -s a.out
Load this a.out in gdb
gdb a.out
gdb says "no debug information found" fine.
Then I use add-symbol-file command in gdb
(gdb) add-symbol-file a.out.debug [Enter]
The address where a.out.debug has been loaded is missing
I want to know how to find this address?
Is there any command or trick to find it?
This address is representing WHAT?
I know gdb has an other command symbol-file but it overwrites the previous loaded symbols.
So I have to use this command to add many symbol files in gdb.
my system is 64bit running ubuntu LTS 12.04
gdb version is 7.4-2012.04
gcc version is 4.6.3

Answer 1

objcopy --only-keep-debug a.out a.out.sym
If you want GDB to load the a.out.sym automatically, follow the steps outlined here (note in particular that you need to do the "add .gnu_debuglink" step).
This address is representing WHAT
The address GDB wants is the location of .text section of the binary. To find it, use readelf -WS a.out. E.g.
$ readelf -WS /bin/date
There are 28 section headers, starting at offset 0xe350:
Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] .interp PROGBITS 0000000000400238 000238 00001c 00 A 0 0 1
...
[13] .text PROGBITS 0000000000401900 001900 0077f8 00 AX 0 0 16
Here, you want to give GDB 0x401900 as the load address.