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| author | Kartik Agaram <vc@akkartik.com> | 2020-01-01 17:23:29 -0800 |
|---|---|---|
| committer | Kartik Agaram <vc@akkartik.com> | 2020-01-01 17:23:29 -0800 |
| commit | 113bae7311b63e55e55160970718d19bfeeb56c3 (patch) | |
| tree | d2468b58470e173329c7ef6e8da496c2f768b037 /apps/ex10.subx | |
| parent | 1b050736eea04323e09e5e8e7499c33cee1899d0 (diff) | |
| download | mu-113bae7311b63e55e55160970718d19bfeeb56c3.tar.gz | |
5856
Diffstat (limited to 'apps/ex10.subx')
| -rw-r--r-- | apps/ex10.subx | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/apps/ex10.subx b/apps/ex10.subx new file mode 100644 index 00000000..c091fe52 --- /dev/null +++ b/apps/ex10.subx @@ -0,0 +1,69 @@ +# String comparison: return 1 iff the two args passed in at the commandline are equal. +# +# To run: +# $ ./subx translate init.linux examples/ex10.subx -o examples/ex10 +# $ ./subx run examples/ex10 abc abd +# Expected result: +# $ echo $? +# 0 # false + +== code +# instruction effective address register displacement immediate +# . op subop mod rm32 base index scale r32 +# . 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes + +Entry: # return argv-equal(argv[1], argv[2]) +# At the start of a SubX program: +# argc: *esp +# argv[0]: *(esp+4) +# argv[1]: *(esp+8) +# ... + # . prologue + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # argv-equal(argv[1], argv[2]) + # . . push argv[2] + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) + # . . push argv[1] + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) + # . . call + e8/call argv-equal/disp32 + # exit(eax) + 89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx + e8/call syscall_exit/disp32 + +# compare two null-terminated ascii strings +# reason for the name: the only place we should have null-terminated ascii strings is from commandline args +argv-equal: # (s1, s2) : null-terminated ascii strings -> eax : boolean + # initialize s1 (ecx) and s2 (edx) + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 1/r32/ecx 4/disp8 . # copy *(esp+4) to ecx + 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 8/disp8 . # copy *(esp+8) to edx +$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 + +# . . vim:nowrap:textwidth=0 |