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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/ex10.subx | |
| parent | 8846a7f85cc04b77b2fe8a67b6d317723437b00c (diff) | |
| download | mu-6e1eeeebfb453fa7c871869c19375ce60fbd7413.tar.gz | |
5485 - promote SubX to top-level
Diffstat (limited to 'examples/ex10.subx')
| -rw-r--r-- | examples/ex10.subx | 72 |
1 files changed, 72 insertions, 0 deletions
diff --git a/examples/ex10.subx b/examples/ex10.subx new file mode 100644 index 00000000..51cc0a8c --- /dev/null +++ b/examples/ex10.subx @@ -0,0 +1,72 @@ +# String comparison: return 1 iff the two args passed in at the commandline are equal. +# +# To run (from the subx directory): +# $ ./subx translate examples/ex10.subx -o examples/ex10 +# $ ./subx run examples/ex10 abc abd +# Expected result: +# $ echo $? +# 0 # false + +== code 0x09000000 +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +Entry: # return argv-equal(argv[1], argv[2]) +# At the start of a SubX program: +# argc: *ESP +# argv[0]: *(ESP+4) +# argv[1]: *(ESP+8) +# ... + # . prolog + 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP + # argv-equal(argv[1], argv[2]) + # . . push argv[2] + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12) + # . . push argv[1] + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 8/disp8 . # push *(EBP+8) + # . . call + e8/call argv-equal/disp32 + # syscall(exit, EAX) + 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX + b8/copy-to-EAX 1/imm32/exit + cd/syscall 0x80/imm8 + +# compare two null-terminated ascii strings +# reason for the name: the only place we should have null-terminated ascii strings is from commandline args +argv-equal: # (s1, s2) : null-terminated ascii strings -> EAX : boolean + # initialize s1 (ECX) and s2 (EDX) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 1/r32/ECX 4/disp8 . # copy *(ESP+4) to ECX + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 2/r32/EDX 8/disp8 . # copy *(ESP+8) to EDX +$argv-equal:loop: + # c1/EAX, c2/EBX = *s1, *s2 + b8/copy-to-EAX 0/imm32 + 8a/copy-byte 0/mod/indirect 1/rm32/ECX . . . 0/r32/AL . . # copy byte at *ECX to AL + bb/copy-to-EBX 0/imm32 + 8a/copy-byte 0/mod/indirect 2/rm32/EDX . . . 3/r32/BL . . # copy byte at *EDX to BL + # if (c1 == 0) break + 3d/compare-EAX-and 0/imm32 + 74/jump-if-equal $argv-equal:break/disp8 + # if (c1 != c2) return false + 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX and EBX + 75/jump-if-not-equal $argv-equal:false/disp8 + # ++s1, ++s2 + 41/increment-ECX + 42/increment-EDX + # end while + eb/jump $argv-equal:loop/disp8 +$argv-equal:break: + # if (c2 == 0) return true + 81 7/subop/compare 3/mod/direct 3/rm32/EBX . . . . . 0/imm32 # compare EBX + 75/jump-if-not-equal $argv-equal:false/disp8 +$argv-equal:success: + b8/copy-to-EAX 1/imm32 + c3/return + # return false +$argv-equal:false: + b8/copy-to-EAX 0/imm32 + c3/return + +== data 0x0a000000 + +# . . vim:nowrap:textwidth=0 |