Hi!
I hope I'm right here. I've the following assembler code:
SECTION .DATA
hello: db 'Hello world!',10
helloLen: equ $-hello
SECTION .TEXT
GLOBAL main
main:
; 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
./hello
segmentation fault
I link it with the gcc and run it:
gcc hello.o -o hello
./hello
Hello world!
What's wrong with the ld?
Matthias-Christian Ott
On Sat, 12 Mar 2005, Matthias-Christian Ott wrote:
> Hi!
> I hope I'm right here. I've the following assembler code:
>
> SECTION .DATA
> hello: db 'Hello world!',10
> helloLen: equ $-hello
>
> SECTION .TEXT
> GLOBAL main
>
> main:
>
>
>
> ; 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
> ./hello
> segmentation fault
>
>
> I link it with the gcc and run it:
>
> gcc hello.o -o hello
> ./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.
Cheers,
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.
linux-os wrote:
> On Sat, 12 Mar 2005, Matthias-Christian Ott wrote:
>
>> Hi!
>> I hope I'm right here. I've the following assembler code:
>>
>> SECTION .DATA
>> hello: db 'Hello world!',10
>> helloLen: equ $-hello
>>
>> SECTION .TEXT
>> GLOBAL main
>>
>> main:
>>
>>
>>
>> ; 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
>> ./hello
>> segmentation fault
>>
>>
>> I link it with the gcc and run it:
>>
>> gcc hello.o -o hello
>> ./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.
>
>
> Cheers,
> 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