CODEWITHSUNDEEP
clinkerobjdump
Whoami
Whoami

Reputation: 14418

relocation entry is not shown in objdump output of given sample program

I have the below sample code. I would like to see the relocation table entries from the object file. For this, i have used

objdump -r test.o

Sample Code:

#include <stdio.h>
char * myfunction ();
int x=20;
int main()
{

  printf (" \n Inside main ");
  char * p = myfunction ();
  printf (" \n My string is %s ", p);
}

char * myfunction ()
{
  char * key ="jaka";
  return key;
}

Outputof Objdump -r test.o

test.o:     file format elf64-x86-64

RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE 
0000000000000009 R_X86_64_32       .rodata
0000000000000013 R_X86_64_PC32     printf-0x0000000000000004
000000000000001d R_X86_64_PC32     myfunction-0x0000000000000004
000000000000002d R_X86_64_32       .rodata+0x0000000000000010
0000000000000037 R_X86_64_PC32     printf-0x0000000000000004
0000000000000045 R_X86_64_32S      .rodata+0x0000000000000024


RELOCATION RECORDS FOR [.eh_frame]:
OFFSET           TYPE              VALUE 
0000000000000020 R_X86_64_PC32     .text
0000000000000040 R_X86_64_PC32     .text+0x000000000000003d

QUESTION:

According to my understanding the global variable 'x' should have been in the relocation table somewhere, which i m unable to locate.

Please help me if i overlooked something here ?

Upvotes: 1

Views: 1590

Answers (1)

Sergio
Sergio

Reputation: 8209

There are shouldn't be any relocation entries related to x because your code doesn't use it. Nevertheless it presents in symbol table, and you can check it with objdump -t

Saying in few words - relocation entry is the thing that helps your code to reference to some object, to link against them. So, if you don't reference x in your code - there won't be any x targeted relocations.

To check it - add, for example, x = 40; in the main() and you'll get the next:

test.o:     file format elf64-x86-64

RELOCATION RECORDS FOR [.text]:
OFFSET           TYPE              VALUE 
0000000000000009 R_X86_64_32       .rodata
0000000000000013 R_X86_64_PC32     printf-0x0000000000000004
000000000000001d R_X86_64_PC32     myfunction-0x0000000000000004
000000000000002d R_X86_64_32       .rodata+0x0000000000000010
0000000000000037 R_X86_64_PC32     printf-0x0000000000000004
000000000000003d R_X86_64_PC32     x-0x0000000000000008         # bingo!
000000000000004f R_X86_64_32S      .rodata+0x0000000000000024


RELOCATION RECORDS FOR [.eh_frame]:
OFFSET           TYPE              VALUE 
0000000000000020 R_X86_64_PC32     .text
0000000000000040 R_X86_64_PC32     .text+0x0000000000000047

Upvotes: 2

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