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| author | Kartik Agaram <vc@akkartik.com> | 2019-07-27 16:01:55 -0700 |
|---|---|---|
| committer | Kartik Agaram <vc@akkartik.com> | 2019-07-27 17:47:59 -0700 |
| commit | 6e1eeeebfb453fa7c871869c19375ce60fbd7413 (patch) | |
| tree | 539c4a3fdf1756ae79770d5c4aaf6366f1d1525e /050_write.subx | |
| parent | 8846a7f85cc04b77b2fe8a67b6d317723437b00c (diff) | |
| download | mu-6e1eeeebfb453fa7c871869c19375ce60fbd7413.tar.gz | |
5485 - promote SubX to top-level
Diffstat (limited to '050_write.subx')
| -rw-r--r-- | 050_write.subx | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/050_write.subx b/050_write.subx new file mode 100644 index 00000000..0d6b8152 --- /dev/null +++ b/050_write.subx @@ -0,0 +1,57 @@ +# _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 |