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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 /examples/ex9.subx | |
| parent | 8846a7f85cc04b77b2fe8a67b6d317723437b00c (diff) | |
| download | mu-6e1eeeebfb453fa7c871869c19375ce60fbd7413.tar.gz | |
5485 - promote SubX to top-level
Diffstat (limited to 'examples/ex9.subx')
| -rw-r--r-- | examples/ex9.subx | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/examples/ex9.subx b/examples/ex9.subx new file mode 100644 index 00000000..e3318b05 --- /dev/null +++ b/examples/ex9.subx @@ -0,0 +1,55 @@ +# Example showing arg order on the stack. +# +# Show difference between ascii codes of first letter of first arg and first +# letter of second arg. +# +# To run (from the subx directory): +# $ ./subx translate examples/ex9.subx -o examples/ex9 +# $ ./subx run examples/ex9 z x +# Expected result: +# $ echo $? +# 2 +# +# At the start of a SubX program: +# argc: *ESP +# argv[0]: *(ESP+4) +# argv[1]: *(ESP+8) +# ... +# Locals start from ESP-4 downwards. + +== code 0x09000000 +# 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: + # . prolog + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # ascii-difference(argv[1], argv[2]) + # . . push argv[2] + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12) + # . . push argv[1] + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8) + # . . call + e8/call ascii-difference/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP + # syscall(exit, EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX + b8/copy-to-EAX 1/imm32/exit + cd/syscall 0x80/imm8 + +ascii-difference: # (s1, s2) : null-terminated ascii strings + # a = first letter of s1 (ECX) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 0/r32/EAX 4/disp8 . # copy *(ESP+4) to EAX + 8b/copy 0/mod/indirect 0/rm32/EAX . . . 0/r32/EAX . . # copy *EAX to EAX + # b = first letter of s2 (EDX) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 1/r32/ECX 8/disp8 # copy *(ESP+8) to ECX + 8b/copy 0/mod/indirect 1/rm32/ECX . . . 1/r32/ECX . . # copy *ECX to ECX + # a-b + 29/subtract 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # subtract ECX from EAX + c3/return + +== data 0x0a000000 + +# . . vim:nowrap:textwidth=0 |