How can I find the **type** or **length** information in the .data section dump file?

Question

Test platform is on 32 bit Linux.

Here is my code:

#include <stdio.h>
#include "calc_mean.h"

extern double  mean(double, double);
extern int aaaa;
static int b;
static int c = 999999999;
static double d;
static float e = 2.0;
static double f = 2.0;

int main(int argc, char* argv[]) {

    double v1, v2, m;
    v1 = 5.2;
    v2 = 7.9;


    aaaa = 100;
    b = 123;
    c = 321;
    d = 13.3;
    e = 122.2;
    e = 123123.123;
    f = 11231233.0;
    f = 111233.0;
    f = 1133.0;
    f = 11231231231233.0;
    e = 33.4;

    printf("%d\n", aaaa);
    printf("asdfjkhadsfkjhadskfjh\n");
    printf("adsjfhaskdjfhakjdshfkajhdsfkjahdfkjh%d\n", aaaa);

    m  = mean(v1, v2);

    printf("The mean of %3.2f and %3.2f is %3.2f\n", v1, v2, m);

    return 0;
}

I use objdump to dump the .data section's content, and here are the info I got.

objdump -s -j .data test

dump info

test:     file format elf32-i386

Contents of section .data:
804a018 00000000 00000000 ffc99a3b 00000040  ...........;...@
804a028 00000000 00000040                    .......@

Then another method:

objdump -D test > dump

here is the .data section in dump

Disassembly of section .data:

0804a018 <__data_start>:
  804a018:       00 00                   add    %al,(%eax)
    ...

0804a01c <__dso_handle>:
  804a01c:       00 00                   add    %al,(%eax)
    ...

0804a020 <c>:
  804a020:       ff c9                   dec    %ecx
  804a022:       9a 3b 00 00 00 40 00    lcall  $0x40,$0x3b

0804a024 <e>:
 804a024:       00 00                   add    %al,(%eax)
 804a026:       00 40 00                add    %al,0x0(%eax)

0804a028 <f>:
  804a028:       00 00                   add    %al,(%eax)
  804a02a:       00 00                   add    %al,(%eax)
  804a02c:       00 00                   add    %al,(%eax)
  804a02e:       00                      .byte 0x0
  804a02f:       40                      inc    %eax

So what I am trying to do is obtaining the variable info(like variable name, length, value) from the dump(and probably with disassembly) info I present

But currently I don't know how to obtain the type info from the dump file, and I think without the type information, I can hardly know the length as well as value of each variable...

Could anyone give me some help?

THank you!

Answer 1

Variable information such as variable name, address, size etc. is usually compiled as DWARF information in the executable. It will only be available when you compile your code with -g flag. Look for section names starting with .dwarf when using objdump or similar tools.