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# _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
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