Re: Strange Linking Problem

From: Matthias-Christian Ott
Date: Sun Mar 13 2005 - 04:35:20 EST

linux-os wrote:

On Sat, 12 Mar 2005, Matthias-Christian Ott wrote:

I hope I'm right here. I've the following assembler code:

hello: db 'Hello world!',10
helloLen: equ $-hello



; Write 'Hello world!' to the screen
mov eax,4 ; 'write' system call
mov ebx,1 ; file descriptor 1 = screen
mov ecx,hello ; string to write
mov edx,helloLen ; length of string to write
int 80h ; call the kernel

; Terminate program
mov eax,1 ; 'exit' system call
mov ebx,0 ; exit with error code 0
int 80h ; call the kernel

Then I run:

nasm -f elf hello.asm

I link it with ld and run it:

ld -s -o hello hello.o
segmentation fault

I link it with the gcc and run it:

gcc hello.o -o hello
Hello world!

What's wrong with the ld?

Nothing at all. Where is _start: ?

Remove the 'main' label and substitute _start:

It is 'C' convention that programs start with main(). They
really don't. With the Linux API, they start at _start: and
do some housekeeping before calling main. That's what the
crt.o file that the 'C' tool-chain uses, does.

Dick Johnson
Penguin : Linux version 2.6.11 on an i686 machine (5537.79 BogoMips).
Notice : All mail here is now cached for review by Dictator Bush.
98.36% of all statistics are fiction.

Ofcourse you have to edit it, but this is not the problem (the linker will give an error message if you don't change it). Why does it cause a segementation fault?

Matthias-Christian Ott
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