Minor Self Modifying Code linker (maybe) bug

I don't know why and why not, but when i specify "format elf executable" my smc code cannot run without a segfault. But when i specify "format elf" and link with ld, my smc code does fine.

Here is my code (linux2.6 debian fasm 1.53)

Code:

format ELF
public start

section ".data" align 0x1000
modified_code rb 0x8000

sys.write = 4
sys.mprotect = 125

macro sys.write fd, buf, count{
        mov eax, 4
        mov ebx, fd
        mov ecx, buf
        mov edx, count
        int 80h
}
read = 1
write = 2
exec = 4

stdout = 1

section ".data"string db "Hello World!", 0xA
sizeof.string = $-string

section ".text"
start:
        mov ebp, modified_code

        mov eax, sys.mprotect
        mov ebx, ebp
        mov ecx, 0x8000
        mov edx, read+write+exec
        int 80h

        test eax, eax
        js .error
.tocopy:
        sys.write stdout, string, sizeof.string

        sizeof.start.tocopy= $-.tocopy

        mov ebx, 90
        mov edi, modified_code
.loop:
        mov esi, .tocopy
        mov ecx, sizeof.start.tocopy
        rep movsb
        dec ebx
        jnz .loop

        mov al, 0xc3
        stosb
        jmp .blah
.blah:

        call ebp
 .error:
        mov eax, 1
        mov ebx, 0
        int 80h

Sorry for the lack of comments. Anyway, when i change it to executable, and then change all the segments to either (writeable readable) or (executeable) it just wont work.

The changes look like this:
from

Code:

section ".data" align 0x1000

Code:

section readable writeable
align 0x1000

if it has to do with anything. And this is applied to all section headers thoughout the source.

Linking with LD works fine however , so i think this is a linker error. No clue though Smile

This should print 91 "Hello World!", 0xa
out