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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <title>Mu - apps/ex10.subx</title> <meta name="Generator" content="Vim/8.1"> <meta name="plugin-version" content="vim8.1_v1"> <meta name="syntax" content="none"> <meta name="settings" content="number_lines,use_css,no_foldcolumn,expand_tabs,line_ids,prevent_copy="> <meta name="colorscheme" content="minimal-light"> <style type="text/css">  </style> <script type='text/javascript'>  </script> </head> <body onload='JumpToLine();'> <a href='https://github.com/akkartik/mu/blob/master/apps/ex10.subx'>https://github.com/akkartik/mu/blob/master/apps/ex10.subx</a> <pre id='vimCodeElement'> 1 # String comparison: return 1 iff the two args passed in at the commandline are equal. 2 # 3 # To run: 4 # $ ./bootstrap translate init.linux apps/ex10.subx -o apps/ex10 5 # $ ./bootstrap run apps/ex10 abc abd 6 # Expected result: 7 # $ echo $? 8 # 0 # false 9 10 == code 11 # instruction effective address register displacement immediate 12 # . op subop mod rm32 base index scale r32 13 # . 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 14 15 Entry: # return argv-equal(argv[1], argv[2]) 16 # At the start of a SubX program: 17 # argc: *esp 18 # argv[0]: *(esp+4) 19 # argv[1]: *(esp+8) 20 # ... 21 # . prologue 22 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp 23 # argv-equal(argv[1], argv[2]) 24 # . . push argv[2] 25 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) 26 # . . push argv[1] 27 ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 8/disp8 . # push *(ebp+8) 28 # . . call 29 e8/call <a href='ex10.subx.html#L36'>argv-equal</a>/disp32 30 # exit(eax) 31 89/copy 3/mod/direct 3/rm32/ebx . . . 0/r32/eax . . # copy eax to ebx 32 e8/call syscall_exit/disp32 33 34 # compare two null-terminated ascii strings 35 # reason for the name: the only place we should have null-terminated ascii strings is from commandline args 36 argv-equal: # (s1, s2): null-terminated ascii strings -> eax: boolean 37 # initialize s1 (ecx) and s2 (edx) 38 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 1/r32/ecx 4/disp8 . # copy *(esp+4) to ecx 39 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/esp 4/index/none . 2/r32/edx 8/disp8 . # copy *(esp+8) to edx 40 $argv-equal:loop: 41 # c1/eax, c2/ebx = *s1, *s2 42 b8/copy-to-eax 0/imm32 43 8a/copy-byte 0/mod/indirect 1/rm32/ecx . . . 0/r32/AL . . # copy byte at *ecx to AL 44 bb/copy-to-ebx 0/imm32 45 8a/copy-byte 0/mod/indirect 2/rm32/edx . . . 3/r32/BL . . # copy byte at *edx to BL 46 # if (c1 == 0) break 47 3d/compare-eax-and 0/imm32/null 48 74/jump-if-= $argv-equal:break/disp8 49 # if (c1 != c2) return false 50 39/compare 3/mod/direct 0/rm32/eax . . . 3/r32/ebx . . # compare eax and ebx 51 75/jump-if-!= $argv-equal:false/disp8 52 # ++s1, ++s2 53 41/increment-ecx 54 42/increment-edx 55 # end while 56 eb/jump $argv-equal:loop/disp8 57 $argv-equal:break: 58 # if (c2 == 0) return true 59 81 7/subop/compare 3/mod/direct 3/rm32/ebx . . . . . 0/imm32/null # compare ebx 60 75/jump-if-!= $argv-equal:false/disp8 61 $argv-equal:success: 62 b8/copy-to-eax 1/imm32 63 c3/return 64 # return false 65 $argv-equal:false: 66 b8/copy-to-eax 0/imm32 67 c3/return 68 69 # . . vim:nowrap:textwidth=0 </pre> </body> </html>