linux-kernel - Address of .globl

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Message-ID: <2d05c4580904201644n58160449n2e917cbac096ceeb@mail.gmail.com>
Date:	Tue, 21 Apr 2009 01:44:36 +0200
From:	Dragoslav Zaric <dragoslav.zaric.kd@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Subject: Address of .globl _start

Hello,

I have compiled test.s (bellow) with 'as' compiler:

-------------------------------------------------
.section .data

.globl var
var:
.long 10

.section .text

.globl _start
_start:
 movl $_start, %ebx
 jmp loop_exit

loop_exit:
  movl $1, %eax             #1 is the exit() syscall
  int $0x80

-------------------------------------------------
and got output with echo $? (reads %ebx register)
116

After that I compiled test.s (bellow) with 'as' compiler:

-------------------------------------------------
.section .data

.globl var
var:
.long 10

.section .text

.globl _start
_start:
 movl _start, %ebx
 jmp loop_exit

loop_exit:
  movl $1, %eax             #1 is the exit() syscall
  int $0x80

-------------------------------------------------
and got output with echo $? (reads %ebx register)
139

After that I compiled test.s (bellow) with 'as' compiler:

-------------------------------------------------
.section .data

.globl var
var:
.long 10

.section .text

.globl _start
_start:
 movl var, %ebx
 jmp loop_exit

loop_exit:
  movl $1, %eax             #1 is the exit() syscall
  int $0x80

-------------------------------------------------
and got output with echo $? (reads %ebx register)
10

After that I compiled test.s (bellow) with 'as' compiler:

-------------------------------------------------
.section .data

.globl var
var:
.long 10

.section .text

.globl _start
_start:
 movl $var, %ebx
 jmp loop_exit

loop_exit:
  movl $1, %eax             #1 is the exit() syscall
  int $0x80

-------------------------------------------------
and got output with echo $? (reads %ebx register)
132

So my question is, what these numbers mean ? From which
point in memory they are counted from ? From this I can conclude
that value for "movl _start, %ebx" is always 139 and it can be on
various addresses. Is this means that beginning of 'as' assembly program is
signed with value 139 ???

thanks,

Dragoslav Zaric,
[Programmer; M Sc Astrophysics]
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