2018-12-03 04:39:21 +00:00
|
|
|
# _write: write to a file descriptor (fd)
|
2018-10-16 07:15:51 +00:00
|
|
|
|
2018-10-01 19:22:59 +00:00
|
|
|
== code
|
2018-11-30 19:10:44 +00:00
|
|
|
# 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
|
2018-10-01 22:12:56 +00:00
|
|
|
|
2021-08-23 04:06:36 +00:00
|
|
|
#? Entry: # just exit; can't test _write just yet
|
|
|
|
#? bb/copy-to-ebx 0/imm32
|
|
|
|
#? e8/call syscall_exit/disp32
|
2018-10-11 05:21:26 +00:00
|
|
|
|
2020-01-27 08:36:44 +00:00
|
|
|
_write: # fd: int, s: (addr array byte)
|
2019-10-16 02:35:19 +00:00
|
|
|
# . prologue
|
2019-08-26 18:55:26 +00:00
|
|
|
55/push-ebp
|
|
|
|
89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp
|
2018-11-30 19:10:44 +00:00
|
|
|
# . save registers
|
2019-08-26 18:55:26 +00:00
|
|
|
50/push-eax
|
|
|
|
51/push-ecx
|
|
|
|
52/push-edx
|
|
|
|
53/push-ebx
|
2021-07-20 14:30:59 +00:00
|
|
|
# syscall_write(fd, (data) s+4, (size) *s)
|
2020-01-27 08:36:44 +00:00
|
|
|
# . ebx = fd
|
2019-08-26 18:55:26 +00:00
|
|
|
8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 3/r32/ebx 8/disp8 . # copy *(ebp+8) to ebx
|
2020-01-27 08:36:44 +00:00
|
|
|
# . var data/ecx: (addr byte) = s+4
|
2019-08-26 18:55:26 +00:00
|
|
|
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
|
2020-01-27 08:36:44 +00:00
|
|
|
# . var size/edx: int = *s
|
2019-08-26 18:55:26 +00:00
|
|
|
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
|
2018-11-30 19:10:44 +00:00
|
|
|
# . syscall
|
2020-06-11 06:09:30 +00:00
|
|
|
e8/call syscall_write/disp32
|
2019-08-26 18:55:26 +00:00
|
|
|
# if (eax < 0) abort
|
|
|
|
3d/compare-eax-with 0/imm32
|
2020-01-17 02:31:12 +00:00
|
|
|
0f 8c/jump-if-< $_write:abort/disp32
|
2018-12-04 08:29:06 +00:00
|
|
|
$_write:end:
|
2018-11-30 19:10:44 +00:00
|
|
|
# . restore registers
|
2019-08-26 18:55:26 +00:00
|
|
|
5b/pop-to-ebx
|
|
|
|
5a/pop-to-edx
|
|
|
|
59/pop-to-ecx
|
|
|
|
58/pop-to-eax
|
2019-10-16 02:35:19 +00:00
|
|
|
# . epilogue
|
2019-08-26 18:55:26 +00:00
|
|
|
89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp
|
|
|
|
5d/pop-to-ebp
|
2018-11-30 18:54:42 +00:00
|
|
|
c3/return
|
2018-10-01 22:12:56 +00:00
|
|
|
|
2019-05-12 05:44:49 +00:00
|
|
|
$_write:abort:
|
|
|
|
# can't write a message here for risk of an infinite loop, so we'll use a special exit code instead
|
2021-07-20 14:30:59 +00:00
|
|
|
# . syscall_exit(255)
|
2019-08-26 18:55:26 +00:00
|
|
|
bb/copy-to-ebx 0xff/imm32
|
2020-06-11 06:09:30 +00:00
|
|
|
e8/call syscall_exit/disp32
|
2019-05-12 05:44:49 +00:00
|
|
|
# never gets here
|
|
|
|
|
2018-11-30 19:10:44 +00:00
|
|
|
# . . vim:nowrap:textwidth=0
|