Some decisions made to make this feel a bit higher level: List of flags rather than ORed together numbers. Options used where helpful. Looked into using an OCaml callback, but of course this doesn’t work (as expected - OCaml didn’t like Multicore!). Currently execve’s a specific binary (/bin/sh), but should be easy to extend. Tricky to know sometimes what to put in C and what to put in OCaml."><metaname=authorcontent="Jake Hillion"><linkrel=canonicalhref=https://blog.hillion.co.uk/posts/weekly-2022-01-17/><linkcrossorigin=anonymoushref=/assets/css/stylesheet.min.48a18943c2fc15c38a372b8dde1f5e5dc0bc64fa6cb90f5a817d2f8c76b7f3ae.cssintegrity="sha256-SKGJQ8L8FcOKNyuN3h9eXcC8ZPpsuQ9agX0vjHa3864="rel="preload stylesheet"as=style><scriptdefercrossorigin=anonymoussrc=/assets/js/highlight.min.b95bacdc39e37a332a9f883b1e78be4abc1fdca2bc1f2641f55e3cd3dabd4d61.jsintegrity="sha256-uVus3DnjejMqn4g7Hni+Srwf3KK8HyZB9V4809q9TWE="onload=hljs.initHighlightingOnLoad()></script>
<script>vardoNotTrack=!1;if(!doNotTrack){window.dataLayer=window.dataLayer||[];functiongtag(){dataLayer.push(arguments)}gtag("js",newDate),gtag("config","G-4CXXF49E7M",{anonymize_ip:!1})}</script><metaproperty="og:title"content="Jake's Weekly - 17th Jan 2022"><metaproperty="og:description"content="ResearchProjectProcessIsolationWroteanOCamlbindingfortheclone3syscall(clone_shim.ml/clone3_stub.c).
Some decisions made to make this feel a bit higher level: List of flags rather than ORed together numbers. Options used where helpful. Looked into using an OCaml callback, but of course this doesn’t work (as expected - OCaml didn’t like Multicore!). Currently execve’s a specific binary (/bin/sh), but should be easy to extend. Tricky to know sometimes what to put in C and what to put in OCaml."><metaproperty="og:type"content="article"><metaproperty="og:url"content="https://blog.hillion.co.uk/posts/weekly-2022-01-17/"><metaproperty="article:section"content="posts"><metaproperty="article:published_time"content="2022-01-15T11:00:00+00:00"><metaproperty="article:modified_time"content="2022-01-15T11:00:00+00:00"><metaproperty="og:site_name"content="Jake Hillion"><metaname=twitter:cardcontent="summary"><metaname=twitter:titlecontent="Jake's Weekly - 17th Jan 2022"><metaname=twitter:descriptioncontent="ResearchProjectProcessIsolationWroteanOCamlbindingfortheclone3syscall(clone_shim.ml/clone3_stub.c).
Some decisions made to make this feel a bit higher level: List of flags rather than ORed together numbers. Options used where helpful. Looked into using an OCaml callback, but of course this doesn’t work (as expected - OCaml didn’t like Multicore!). Currently execve’s a specific binary (/bin/sh), but should be easy to extend. Tricky to know sometimes what to put in C and what to put in OCaml."><scripttype=application/ld+json>{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Posts","item":"https://blog.hillion.co.uk/posts/"},{"@type":"ListItem","position":2,"name":"Jake's Weekly - 17th Jan 2022","item":"https://blog.hillion.co.uk/posts/weekly-2022-01-17/"}]}</script><scripttype=application/ld+json>{"@context":"https://schema.org","@type":"BlogPosting","headline":"Jake'sWeekly-17thJan2022","name":"Jake\u0027sWeekly-17thJan2022","description":"ResearchProjectProcessIsolationWroteanOCamlbindingfortheclone3syscall(clone_shim.ml/clone3_stub.c).\nSomedecisionsmadetomakethisfeelabithigherlevel:ListofflagsratherthanORedtogethernumbers.Optionsusedwherehelpful.LookedintousinganOCamlcallback,butofcoursethisdoesn\u0026rsquo;twork(asexpected-OCamldidn\u0026rsquo;tlikeMulticore!).Currentlyexecve\u0026rsquo;saspecificbinary(/bin/sh),butshouldbeeasytoextend.TrickytoknowsometimeswhattoputinCandwhattoputinOCaml.","keywords":[],"articleBody":"ResearchProjectProcessIsolationWroteanOCamlbindingfortheclone3syscall(clone_shim.ml/clone3_stub.c).\nSomedecisionsmadetomakethisfeelabithigherlevel:ListofflagsratherthanORedtogethernumbers.Optionsusedwherehelpful.LookedintousinganOCamlcallback,butofcoursethisdoesn’twork(asexpected-OCamldidn’tlikeMulticore!).Currentlyexecve’saspecificbinary(/bin/sh),butshouldbeeasytoextend.TrickytoknowsometimeswhattoputinCandwhattoputinOCaml.Ithinkthiswillbecomemoreclearcutastimegoeson,butfornowit’squitechallenging.It’snicetosayargcheckinginOCamlleavingsimplythesyscallforC,butsomeoftheissuesaren’tclearuntilthetypesareconvertedtofinalinC.Thecurrentshimusesidenticalargumentstounshare(1)soeasytocompareperformance.WrotesomeOCaml.\nNotashardtogetstartedasI’dworried,certainlygood.Argumentparsingisprettysimpleandtheappstructureitselfisokay.63-bitintsworrymequitealot(perhapsmorethantheyshould).AlotofcheckingwhenworkingwithsyscallsandCtoensurethat63-bitsisenoughforeachspecificapplication.Setupmydevmachine.\nUbuntu20.04LTSfeelsabitlimitingforthistask.Thekernelisatadoldandsomeofthebindings/manpagesareoutofdate.WillcheckwithsysadminaboutconstraintsforreplacingtheOS.Wouldalsobeusefultohaveaccesstosomemoreportsformydevelopmentworkflow,sowillrunthisbysysadmintoo.Beganworkonaptracedebuggerformultiprocessapplications.\nI’vewrittensomelightptracestuffbefore,sogettingstartedwasn’ttoohard.ThoughI’dliketomakethisdebuggerquitegeneral,it’simportantfornowtokeepthescopeofitwithintheproject-ifI’monlyusingclone3andnotfork,supportingforkisunnecessary.NoGUIyetandnotsuperuseful,butcertainlygettingthere.UpNextGetthecloneshimrunningarbitraryapplications.Currentlyitrunsashell,whichisfineandusefulfordebugging.Runningmoreapplicationsisobviouslynecessarytocontinue.Continuewithtracingthisapplicationtoensureaviewofwhat’sgoingonisavailable,particularlyasthingsgetmorecomplicated.BiggerCprogramstotestwitharecontinuingtobeimportant-notmuchprogressmadeonthisfrontinthepastcoupleofweeks.Researchbinformatmiscmore.InthebackofmymindI’mdevelopinganideathatthiscouldbecomeintegraltothisproject.RatherthanmakingbigchangestoOCaml,thiscouldbeus
<spanclass=logo-switches><buttonid=theme-toggleaccesskey=ttitle="(Alt + T)"><svgid="moon"xmlns="http://www.w3.org/2000/svg"width="24"height="24"viewBox="0 0 24 24"fill="none"stroke="currentcolor"stroke-width="2"stroke-linecap="round"stroke-linejoin="round"><pathd="M21 12.79A9 9 0 1111.21 3 7 7 0 0021 12.79z"/></svg><svgid="sun"xmlns="http://www.w3.org/2000/svg"width="24"height="24"viewBox="0 0 24 24"fill="none"stroke="currentcolor"stroke-width="2"stroke-linecap="round"stroke-linejoin="round"><circlecx="12"cy="12"r="5"/><linex1="12"y1="1"x2="12"y2="3"/><linex1="12"y1="21"x2="12"y2="23"/><linex1="4.22"y1="4.22"x2="5.64"y2="5.64"/><linex1="18.36"y1="18.36"x2="19.78"y2="19.78"/><linex1="1"y1="12"x2="3"y2="12"/><linex1="21"y1="12"x2="23"y2="12"/><linex1="4.22"y1="19.78"x2="5.64"y2="18.36"/><linex1="18.36"y1="5.64"x2="19.78"y2="4.22"/></svg></button></span></div><ulid=menu><li><ahref=https://blog.hillion.co.uk/categories/title=categories><span>categories</span></a></li><li><ahref=https://blog.hillion.co.uk/tags/title=tags><span>tags</span></a></li></ul></nav></header><mainclass=main><articleclass=post-single><headerclass=post-header><divclass=breadcrumbs><ahref=https://blog.hillion.co.uk/>Home</a> » <ahref=https://blog.hillion.co.uk/posts/>Posts</a></div><h1class=post-title>Jake's Weekly - 17th Jan 2022</h1><divclass=post-meta><spantitle='2022-01-15 11:00:00 +0000 UTC'>January 15, 2022</span> · 3 min · Jake Hillion</div></header><divclass=post-content><h2id=research-project>Research Project<ahiddenclass=anchoraria-hidden=truehref=#research-project>#</a></h2><h3id=process-isolation>Process Isolation<ahiddenclass=anchoraria-hidden=truehref=#process-isolation>#</a></h3><ul><li><p>Wrote an OCaml binding for the <code>clone3</code> syscall (<ahref=https://gitea.hillion.co.uk/JakeHillion/ocaml-cgroups2/src/commit/0d7c7f7f201eb4664187fbde03d38e4736cabaaa/tools/clone/clone_shim.ml>clone_shim.ml</a>/<ahref=https://gitea.hillion.co.uk/JakeHillion/ocaml-cgroups2/src/commit/0d7c7f7f201eb4664187fbde03d38e4736cabaaa/tools/clone/clone3_stub.c>clone3_stub.c</a>).</p><ul><li>Some decisions made to make this feel a bit higher level:<ul><li>List of flags rather than ORed together numbers.</li><li>Options used where helpful.</li><li>Looked into using an OCaml callback, but of course this doesn’t work (as expected - OCaml didn’t like Multicore!). Currently execve’s a specific binary (<code>/bin/sh</code>), but should be easy to extend.</li></ul></li><li>Tricky to know sometimes what to put in C and what to put in OCaml.<ul><li>I think this will become more clear cut as time goes on, but for now it’s quite challenging.</li><li>It’s nice to say arg checking in OCaml leaving simply the syscall for C, but some of the issues aren’t clear until the types are converted to final in C.</li></ul></li><li>The current shim uses identical arguments to <code>unshare(1)</code> so easy to compare performance.</li></ul></li><li><p>Wrote some OCaml.</p><ul><li>Not as hard to get started as I’d worried, certainly good.</li><li>Argument parsing is pretty simple and the app structure itself is okay.</li><li>63-bit ints worry me quite a lot (perhaps more than they should). A lot of checking when working with syscalls and C to ensure that 63-bits is enough for each specific application.</li></ul></li><li><p>Set up my dev machine.</p><ul><li>Ubuntu 20.04LTS feels a bit limiting for this task. The kernel is a tad old and some of the bindings/man pages are out of date. Will check with sysadmin about constraints for replacing the OS.</li><li>Would also be useful to have access to some more ports for my development workflow, so will run this by sysadmin too.</li></ul></li><li><p>Began work on a ptrace debugger for multiprocess applications.</p><ul><li>I’ve written some light ptrace stuff before, so getting started wasn’t too hard.</li><li>Though I’d like to make this debugger quite general, it&rsq
<ahref=https://git.io/hugopapermodrel=noopenertarget=_blank>PaperMod</a></span></footer><ahref=#toparia-label="go to top"title="Go to Top (Alt + G)"class=top-linkid=top-linkaccesskey=g><svgxmlns="http://www.w3.org/2000/svg"viewBox="0 0 12 6"fill="currentcolor"><pathd="M12 6H0l6-6z"/></svg></a><script>letmenu=document.getElementById("menu");menu&&(menu.scrollLeft=localStorage.getItem("menu-scroll-position"),menu.onscroll=function(){localStorage.setItem("menu-scroll-position",menu.scrollLeft)}),document.querySelectorAll('a[href^="#"]').forEach(e=>{e.addEventListener("click",function(e){e.preventDefault();vart=this.getAttribute("href").substr(1);window.matchMedia("(prefers-reduced-motion: reduce)").matches?document.querySelector(`[id='${decodeURIComponent(t)}']`).scrollIntoView():document.querySelector(`[id='${decodeURIComponent(t)}']`).scrollIntoView({behavior:"smooth"}),t==="top"?history.replaceState(null,null," "):history.pushState(null,null,`#${t}`)})})</script><script>varmybutton=document.getElementById("top-link");window.onscroll=function(){document.body.scrollTop>800||document.documentElement.scrollTop>800?(mybutton.style.visibility="visible",mybutton.style.opacity="1"):(mybutton.style.visibility="hidden",mybutton.style.opacity="0")}</script><script>document.getElementById("theme-toggle").addEventListener("click",()=>{document.body.className.includes("dark")?(document.body.classList.remove("dark"),localStorage.setItem("pref-theme","light")):(document.body.classList.add("dark"),localStorage.setItem("pref-theme","dark"))})</script></body></html>
