[lug] Linux syscall 19 lseek() produces unexpected output

[Carl Hamlin]

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Folks, I am *really* stumped. Here's the code:

section .data

	fd1	dd	0
	testd	db	'Generic Text'
	testsz	equ	$ - testd

section .text
global	_start

_start:

	pop	ebx		;	ebx - argc
	pop	ebx		;	ebx - argv
	pop	ebx		;	ebx - filename to write to
	
	mov	eax, 8		;	eax - syscall_creat
	mov	ecx, 00664Q	;	ecx - read/write
	int	80h		;	syscall_creat
	mov	[fd1], eax	;	eax - file descriptor
	
	mov	eax, 19		;	eax - syscall_lseek
	mov	ebx, [fd1]	;	ebx - file descriptor
	sub	ecx, ecx	;	ecx - offset 0
	sub	edx, 2		;	edx - SEEK_END
	int	80h		;	syscall_lseek
	
	mov	eax, 4		;	eax - syscall_write
	mov	ebx, [fd1]	;	ebx - file descriptor
	mov	ecx, testd	;	ecx - pointer to data to be
				;	      written
	mov	edx, testsz	;	edx - number of bytes to be
				;	      written
	int	80h		;	syscall_write
	
	mov	eax, 1		;	eax - syscall_exit
	sub	ebx, ebx	;	ebx - errorcode 0
	int	80h		;	syscall_exit

This code *should* write 'Generic Text' at the end of a file specified
on the command line.

What it does instead is to overwrite the file, if it exists. I've tried
using open() instead of creat() with no luck. There is *very* little
documentation on this on the internet, and believe me, if there is
something that specifically referenced lseek(), I've seen it. This is my
third day trying to figure this out.

Can anyone tell me what gives here?

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