tour - touring some programming systems

	Commit message (Expand)	Author	Age	Files	Lines
*	*	elioat	2024-06-09	1	-12/+1
*	*	elioat	2024-06-09	1	-3/+3
*	*	elioat	2024-06-09	1	-2/+2
*	*	elioat	2024-06-09	1	-10/+24
*	*	elioat	2024-06-09	1	-14/+22
*	*	elioat	2024-06-09	1	-0/+21

<!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 - subx/examples/ex10.subx</title> <meta name="Generator" content="Vim/8.0"> <meta name="plugin-version" content="vim7.4_v2"> <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/subx/examples/ex10.subx'>https://github.com/akkartik/mu/blob/master/subx/examples/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 (from the subx directory): 4 # $ ./subx translate examples/ex10.subx -o examples/ex10 5 # $ ./subx run examples/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 # main: 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 # . prolog 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#L37'>argv-equal</a>/disp32 30 # syscall(exit, EAX) 31 89/copy 3/mod/direct 3/rm32/EBX . . . 0/r32/EAX . . # copy EAX to EBX 32 b8/copy-to-EAX 1/imm32/exit 33 cd/syscall 0x80/imm8 34 35 # compare two null-terminated ascii strings 36 # reason for the name: the only place we should have null-terminated ascii strings is from commandline args 37 <a href='ex10.subx.html#L37'>argv-equal</a>: # (s1, s2) : null-terminated ascii strings -> EAX : boolean 38 # initialize s1 (ECX) and s2 (EDX) 39 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 1/r32/ECX 4/disp8 . # copy *(ESP+4) to ECX 40 8b/copy 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none . 2/r32/EDX 8/disp8 . # copy *(ESP+8) to EDX 41 # while (true) 42 $argv-equal:loop: 43 # c1/EAX, c2/EBX = *s1, *s2 44 b8/copy-to-EAX 0/imm32 45 8a/copy 0/mod/indirect 1/rm32/ECX . . . 0/r32/EAX . . # copy byte at *ECX to lower byte of EAX 46 bb/copy-to-EBX 0/imm32 47 8a/copy 0/mod/indirect 2/rm32/EDX . . . 3/r32/EBX . . # copy byte at *EDX to lower byte of EBX 48 # if (c1 == 0) break 49 3d/compare-EAX 0/imm32 50 74/jump-if-equal $argv-equal:break/disp8 51 # if (c1 != c2) return false 52 39/compare 3/mod/direct 0/rm32/EAX . . . 3/r32/EBX . . # compare EAX with EBX 53 75/jump-if-not-equal $argv-equal:false/disp8 54 # ++s1, ++s2 55 41/inc-ECX 56 42/inc-EDX 57 # end while 58 eb/jump $argv-equal:loop/disp8 59 $argv-equal:break: 60 # if (c2 == 0) return true 61 81 7/subop/compare 3/mod/direct 3/rm32/EBX . . . . . 0/imm32 # compare EBX 62 75/jump-if-not-equal $argv-equal:false/disp8 63 $argv-equal:success: 64 b8/copy-to-EAX 1/imm32 65 c3/return 66 # return false 67 $argv-equal:false: 68 b8/copy-to-EAX 0/imm32 69 c3/return 70 71 # . . vim:nowrap:textwidth=0 </pre> </body> </html>