<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Mu - linux/103kernel-string-equal.subx</title>
<meta name="Generator" content="Vim/8.2">
<meta name="plugin-version" content="vim8.1_v2">
<meta name="syntax" content="none">
<meta name="settings" content="number_lines,use_css,no_foldcolumn,expand_tabs,line_ids,prevent_copy=,use_input_for_pc=fallback">
<meta name="colorscheme" content="minimal-light">
<style>
<!--
pre { font-family: monospace; color: #000000; background-color: #ffffd7; }
body { font-size:12pt; font-family: monospace; color: #000000; background-color: #ffffd7; }
a { color:inherit; }
* { font-size:12pt; font-size: 1em; }
.subxComment { color: #005faf; }
.subxS2Comment { color: #8a8a8a; }
.LineNr { }
.subxFunction { color: #af5f00; text-decoration: underline; }
.subxS1Comment { color: #0000af; }
.Constant { color: #008787; }
.SpecialChar { color: #d70000; }
.Normal { color: #000000; background-color: #ffffd7; padding-bottom: 1px; }
.subxMinorFunction { color: #875f5f; }
.subxTest { color: #5f8700; }
.subxH1Comment { color: #005faf; text-decoration: underline; }
-->
</style>
<script>
<!--
/* function to open any folds containing a jumped-to line before jumping to it */
function JumpToLine()
{
var lineNum;
lineNum = window.location.hash;
lineNum = lineNum.substr(1); /* strip off '#' */
if (lineNum.indexOf('L') == -1) {
lineNum = 'L'+lineNum;
}
var lineElem = document.getElementById(lineNum);
/* Always jump to new location even if the line was hidden inside a fold, or
* we corrected the raw number to a line ID.
*/
if (lineElem) {
lineElem.scrollIntoView(true);
}
return true;
}
if ('onhashchange' in window) {
window.onhashchange = JumpToLine;
}
-->
</script>
</head>
<body onload='JumpToLine();'>
<a href='https://github.com/akkartik/mu/blob/main/linux/103kernel-string-equal.subx'>https://github.com/akkartik/mu/blob/main/linux/103kernel-string-equal.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># Checking null-terminated strings.</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxComment">#</span>
<span id="L3" class="LineNr"> 3 </span><span class="subxComment"># By default we create strings as arrays of bytes, and all arrays have a 4-byte</span>
<span id="L4" class="LineNr"> 4 </span><span class="subxComment"># size prefix.</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment">#</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxComment"># However, we sometimes need to deal with null-terminated strings when</span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># interacting with the Linux kernel. This layer implements a function for</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># comparing a null-terminated 'kernel string' with a size-prefixed 'SubX</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxComment"># string'.</span>
<span id="L10" class="LineNr"> 10 </span><span class="subxComment">#</span>
<span id="L11" class="LineNr"> 11 </span><span class="subxComment"># To run (from the subx directory):</span>
<span id="L12" class="LineNr"> 12 </span><span class="subxComment"># $ bootstrap/bootstrap translate 10[0-3]*.subx -o a.elf</span>
<span id="L13" class="LineNr"> 13 </span><span class="subxComment"># $ bootstrap/bootstrap run a.elf # runs a series of tests</span>
<span id="L14" class="LineNr"> 14 </span><span class="subxComment"># ...... # all tests pass</span>
<span id="L15" class="LineNr"> 15 </span><span class="subxComment">#</span>
<span id="L16" class="LineNr"> 16 </span><span class="subxComment"># (We can't yet run the tests when given a "test" commandline argument,</span>
<span id="L17" class="LineNr"> 17 </span><span class="subxComment"># because checking for it would require the function being tested! Breakage</span>
<span id="L18" class="LineNr"> 18 </span><span class="subxComment"># would cause tests to not run, rather than to fail as we'd like.)</span>
<span id="L19" class="LineNr"> 19 </span>
<span id="L20" class="LineNr"> 20 </span>== code
<span id="L21" class="LineNr"> 21 </span><span class="subxComment"># instruction effective address register displacement immediate</span>
<span id="L22" class="LineNr"> 22 </span><span class="subxS1Comment"># . op subop mod rm32 base index scale r32</span>
<span id="L23" class="LineNr"> 23 </span><span class="subxS1Comment"># . 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</span>
<span id="L24" class="LineNr"> 24 </span>
<span id="L25" class="LineNr"> 25 </span><span class="SpecialChar">Entry</span>: <span class="subxComment"># run all tests</span>
<span id="L26" class="LineNr"> 26 </span> e8/call run-tests/disp32 <span class="subxComment"># 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'.</span>
<span id="L27" class="LineNr"> 27 </span> <span class="subxComment"># syscall(exit, Num-test-failures)</span>
<span id="L28" class="LineNr"> 28 </span> 8b/copy 0/mod/indirect 5/rm32/.disp32 <span class="Normal"> . </span> <span class="Normal"> . </span> 3/r32/ebx <span class="SpecialChar"><a href='102test.subx.html#L89'>Num-test-failures</a></span>/disp32 <span class="subxComment"># copy *Num-test-failures to ebx</span>
<span id="L29" class="LineNr"> 29 </span> e8/call <a href='000init.subx.html#L18'>syscall_exit</a>/disp32
<span id="L30" class="LineNr"> 30 </span>
<span id="L31" class="LineNr"> 31 </span><span class="subxFunction">kernel-string-equal?</span>: <span class="subxComment"># s: (addr kernel-string), benchmark: (addr array byte) -> result/eax: boolean</span>
<span id="L32" class="LineNr"> 32 </span> <span class="subxComment"># pseudocode:</span>
<span id="L33" class="LineNr"> 33 </span> <span class="subxComment"># n = benchmark->size</span>
<span id="L34" class="LineNr"> 34 </span> <span class="subxComment"># s1 = s</span>
<span id="L35" class="LineNr"> 35 </span> <span class="subxComment"># s2 = benchmark->data</span>
<span id="L36" class="LineNr"> 36 </span> <span class="subxComment"># i = 0</span>
<span id="L37" class="LineNr"> 37 </span> <span class="subxComment"># while (i < n)</span>
<span id="L38" class="LineNr"> 38 </span> <span class="subxComment"># c1 = *s1</span>
<span id="L39" class="LineNr"> 39 </span> <span class="subxComment"># c2 = *s2</span>
<span id="L40" class="LineNr"> 40 </span> <span class="subxComment"># if (c1 == 0) return false</span>
<span id="L41" class="LineNr"> 41 </span> <span class="subxComment"># if (c1 != c2) return false</span>
<span id="L42" class="LineNr"> 42 </span> <span class="subxComment"># ++s1, ++s2, ++i</span>
<span id="L43" class="LineNr"> 43 </span> <span class="subxComment"># return *s1 == 0</span>
<span id="L44" class="LineNr"> 44 </span> <span class="subxComment">#</span>
<span id="L45" class="LineNr"> 45 </span> <span class="subxComment"># registers:</span>
<span id="L46" class="LineNr"> 46 </span> <span class="subxComment"># i: ecx</span>
<span id="L47" class="LineNr"> 47 </span> <span class="subxComment"># n: edx</span>
<span id="L48" class="LineNr"> 48 </span> <span class="subxComment"># s1: edi</span>
<span id="L49" class="LineNr"> 49 </span> <span class="subxComment"># s2: esi</span>
<span id="L50" class="LineNr"> 50 </span> <span class="subxComment"># c1: eax</span>
<span id="L51" class="LineNr"> 51 </span> <span class="subxComment"># c2: ebx</span>
<span id="L52" class="LineNr"> 52 </span> <span class="subxComment">#</span>
<span id="L53" class="LineNr"> 53 </span> <span class="subxS1Comment"># . prologue</span>
<span id="L54" class="LineNr"> 54 </span> 55/push-ebp
<span id="L55" class="LineNr"> 55 </span> 89/copy 3/mod/direct 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 4/r32/esp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># copy esp to ebp</span>
<span id="L56" class="LineNr"> 56 </span> <span class="subxS1Comment"># . save registers</span>
<span id="L57" class="LineNr"> 57 </span> 51/push-ecx
<span id="L58" class="LineNr"> 58 </span> 52/push-edx
<span id="L59" class="LineNr"> 59 </span> 53/push-ebx
<span id="L60" class="LineNr"> 60 </span> 56/push-esi
<span id="L61" class="LineNr"> 61 </span> 57/push-edi
<span id="L62" class="LineNr"> 62 </span> <span class="subxComment"># var s1/edi: (addr byte) = s</span>
<span id="L63" class="LineNr"> 63 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 7/r32/edi 8/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+8) to edi</span>
<span id="L64" class="LineNr"> 64 </span> <span class="subxComment"># var n/edx: int = benchmark->size</span>
<span id="L65" class="LineNr"> 65 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 2/r32/edx 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+12) to edx</span>
<span id="L66" class="LineNr"> 66 </span> 8b/copy 0/mod/indirect 2/rm32/edx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 2/r32/edx <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="subxComment"># copy *edx to edx</span>
<span id="L67" class="LineNr"> 67 </span> <span class="subxComment"># var s2/esi: (addr byte) = benchmark->data</span>
<span id="L68" class="LineNr"> 68 </span> 8b/copy 1/mod/*+disp8 5/rm32/ebp <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 6/r32/esi 0xc/disp8 <span class="Normal"> . </span> <span class="subxComment"># copy *(ebp+12) to esi</span>
<span id="L69" class="LineNr"> 69 </span> 81 0/subop/add 3/mod/direct 6/rm32/esi <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> <span class="Normal"> . </span> 4/imm32 <span class="subxComment"># add to esi</span>
<span id="L70" class="LineNr"> 70 </span> <span class