58 lines
2.7 KiB
Plaintext
58 lines
2.7 KiB
Plaintext
# _write: write to a file descriptor (fd)
|
|
|
|
== code
|
|
# instruction effective address register displacement immediate
|
|
# . op subop mod rm32 base index scale r32
|
|
# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
|
|
|
|
Entry: # just exit; can't test _write just yet
|
|
# . syscall(exit, 0)
|
|
bb/copy-to-EBX 0/imm32
|
|
b8/copy-to-EAX 1/imm32/exit
|
|
cd/syscall 0x80/imm8
|
|
|
|
_write: # fd : int, s : (address array byte) -> <void>
|
|
# . prolog
|
|
55/push-EBP
|
|
89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP
|
|
# . save registers
|
|
50/push-EAX
|
|
51/push-ECX
|
|
52/push-EDX
|
|
53/push-EBX
|
|
# syscall(write, fd, (data) s+4, (size) *s)
|
|
# . fd : EBX
|
|
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 3/r32/EBX 8/disp8 . # copy *(EBP+8) to EBX
|
|
# . data : ECX = s+4
|
|
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 1/r32/ECX 0xc/disp8 . # copy *(EBP+12) to ECX
|
|
81 0/subop/add 3/mod/direct 1/rm32/ECX . . . . . 4/imm32 # add to ECX
|
|
# . size : EDX = *s
|
|
8b/copy 1/mod/*+disp8 5/rm32/EBP . . . 2/r32/EDX 0xc/disp8 . # copy *(EBP+12) to EDX
|
|
8b/copy 0/mod/indirect 2/rm32/EDX . . . 2/r32/EDX . . # copy *EDX to EDX
|
|
# . syscall
|
|
b8/copy-to-EAX 4/imm32/write
|
|
cd/syscall 0x80/imm8
|
|
# if (EAX < 0) abort
|
|
3d/compare-EAX-with 0/imm32
|
|
0f 8c/jump-if-lesser $_write:abort/disp32
|
|
$_write:end:
|
|
# . restore registers
|
|
5b/pop-to-EBX
|
|
5a/pop-to-EDX
|
|
59/pop-to-ECX
|
|
58/pop-to-EAX
|
|
# . epilog
|
|
89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP
|
|
5d/pop-to-EBP
|
|
c3/return
|
|
|
|
$_write:abort:
|
|
# can't write a message here for risk of an infinite loop, so we'll use a special exit code instead
|
|
# . syscall(exit, 255)
|
|
bb/copy-to-EBX 0xff/imm32
|
|
b8/copy-to-EAX 1/imm32/exit
|
|
cd/syscall 0x80/imm8
|
|
# never gets here
|
|
|
|
# . . vim:nowrap:textwidth=0
|