Arch Linux

Description:

when one of the operand of the mov instruction is an memory address of an label, the as command
actually interpret it as $0x0. while the same file is assembled correctly on Ubuntu and MinGW(Windows)

Additional info:
* package version(s)
* config and/or log files etc.


Steps to reproduce:

create a file test.s

/* test.s */
.code16

mov $0x07C0, %ax /* Set up 4K stack space after this bootloader*/
add $288, %ax /* (4096 + 512) / 16 bytes per paragraph*/
mov %ax, %ss
mov $4096, %sp
mov $0x07C0, %ax /* Set data segment to where we're loaded*/
mov %ax, %ds


/* I also tried mov $LC0, %si */
mov LC0, %si
call print_string

jmp .

print_string:
mov $0x0e, %ah
_loop:
lodsb
cmp $0, %al
je _done
int $0x10
jmp _loop
_done:
ret

LC0:
.ascii "Hello world"
.byte 0
.byte 0

execute:

as test.s -o print

and then execute

objdump print.o -d -m i8086

The result is:

Disassembly of section .text:

0000000000000000 <print_string-0x18>:
0: b8 c0 07 mov $0x7c0,%ax
3: 05 20 01 add $0x120,%ax
6: 8e d0 mov %ax,%ss
8: bc 00 10 mov $0x1000,%sp
b: b8 c0 07 mov $0x7c0,%ax
e: 8e d8 mov %ax,%ds
10: be 00 00 mov $0x0,%si
13: e8 02 00 call 18 <print_string>
16: eb fe jmp 16 <print_string-0x2>

0000000000000018 <print_string>:
18: b4 0e mov $0xe,%ah

000000000000001a <_loop>:
1a: ac lods %ds:(%si),%al
1b: 3c 00 cmp $0x0,%al
1d: 74 04 je 23 <_done>
1f: cd 10 int $0x10
21: eb f7 jmp 1a <_loop>

0000000000000023 <_done>:
23: c3 ret

0000000000000024 <LC0>:
24: 48 dec %ax
25: 65 gs
26: 6c insb (%dx),%es:(%di)
27: 6c insb (%dx),%es:(%di)
28: 6f outsw %ds:(%si),(%dx)
29: 20 77 6f and %dh,0x6f(%bx)
2c: 72 6c jb 9a <LC0+0x76>
2e: 64 00 00 add %al,%fs:(%bx,%si)

Note 10: be 00 00 mov $0x0,%si
in which LC0 is replace by $0x0, while LC0 is not at the address 0x0