Here's a small NASM program:
[BITS 64]
[ORG 0x0000000000200000]
b_print_newline equ 0x0000000000100040
start:
call b_print_newline
ret
Assemble it:
$ nasm -f bin pr-nl-a.asm -o pr-nl-a.app
Disassemble it:
$ objdump -D -b binary -m i386:x86-64 pr-nl-a.app
pr-nl-a.app: file format binary
Disassembly of section .data:
0000000000000000 <.data>:
0: e8 3b 00 f0 ff callq 0xfffffffffff00040
5: c3 retq
Here's a GAS version:
.set b_print_newline , 0x0000000000100040
.text
.global _start
_start:
call b_print_newline
ret
Assemble and link it:
$ as -o pr-nl-b.o pr-nl-b.s
$ ld -Ttext 200000 --oformat binary -o pr-nl-b.app pr-nl-b.o
Disassemble it:
$ objdump -D -b binary -m i386:x86-64 pr-nl-b.app
pr-nl-b.app: file format binary
Disassembly of section .data:
0000000000000000 <.data>:
0: ff 14 25 40 00 10 00 callq *0x100040
7: c3 retq
As you can see, the disassembled code differs slightly. The code for call in NASM:
0: e8 3b 00 f0 ff callq 0xfffffffffff00040
vs GAS:
0: ff 14 25 40 00 10 00 callq *0x100040
Any suggestions for how to implement the GAS version properly?
Here's the program in FASM:
b_print_newline equ 0x0000000000100040
use64
org 0x0000000000200000
start: call b_print_newline
ret
It does the right thing:
$ objdump -D -b binary -m i386:x86-64 pr-nl-c.app
pr-nl-c.app: file format binary
Disassembly of section .data:
0000000000000000 <.data>:
0: e8 3b 00 f0 ff callq 0xfffffffffff00040
5: c3 retq
