<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<!--[if !mso]><style>v\:* {behavior:url(#default#VML);}
o\:* {behavior:url(#default#VML);}
w\:* {behavior:url(#default#VML);}
.shape {behavior:url(#default#VML);}
</style><![endif]--><style><!--
/* Font Definitions */
@font-face
{font-family:Helvetica;
panose-1:2 11 6 4 2 2 2 2 2 4;}
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
p.MsoListParagraph, li.MsoListParagraph, div.MsoListParagraph
{mso-style-priority:34;
mso-margin-top-alt:auto;
margin-right:0in;
mso-margin-bottom-alt:auto;
margin-left:0in;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
span.apple-converted-space
{mso-style-name:apple-converted-space;}
span.EmailStyle22
{mso-style-type:personal-reply;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-size:10.0pt;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
/* List Definitions */
@list l0
{mso-list-id:373314227;
mso-list-template-ids:-769223386;}
ol
{margin-bottom:0in;}
ul
{margin-bottom:0in;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple" style="word-wrap:break-word">
<div class="WordSection1">
<p class="MsoNormal">Static global will not work for XIP<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Mike<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<div style="border:none;border-left:solid blue 1.5pt;padding:0in 0in 0in 4.0pt">
<div>
<div style="border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0in 0in 0in">
<p class="MsoNormal"><b>From:</b> Andrew (EFI) Fish <afish@apple.com> <br>
<b>Sent:</b> Thursday, May 18, 2023 9:49 AM<br>
<b>To:</b> edk2-devel-groups-io <devel@edk2.groups.io>; Kinney, Michael D <michael.d.kinney@intel.com><br>
<b>Cc:</b> Ni, Ray <ray.ni@intel.com>; Rebecca Cran <rebecca@bsdio.com><br>
<b>Subject:</b> Re: [edk2-devel] CpuDeadLoop() is optimized by compiler<o:p></o:p></p>
</div>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Mike,<o:p></o:p></p>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">I pinged some compiler experts to see if our code is correct, or if the compiler has an issue. Seems to be trending compiler issue right now, but I’ve NOT gotten feedback from anyone on the spec committee yet. <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">If we move Index to a static global that would likely work around the compiler issue.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<div>
<p class="MsoNormal">Andrew Fish<o:p></o:p></p>
<div>
<p class="MsoNormal"><br>
<br>
<o:p></o:p></p>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal">On May 18, 2023, at 8:36 AM, Michael D Kinney <<a href="mailto:michael.d.kinney@intel.com">michael.d.kinney@intel.com</a>> wrote:<o:p></o:p></p>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
<div>
<div>
<p class="MsoNormal">Hi Ray,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">So the code generated does deadloop, but is just not easy to resume from as we have been able to do in the past.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">We use CpuDeadloop() for 2 purposes. One is a terminal condition with no reason to ever continue.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">The 2<sup>nd</sup><span class="apple-converted-space"> </span>is a debug aide for developers to halt the system at a specific location and then continue from that point, usually with a debugger, to step through code to an area to evaluate
unexpected behavior.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">We may have to do a NASM implementation of CpuDeadloop() to make sure it meets both use cases.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Mike<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div style="border:none;border-left:solid windowtext 1.5pt;padding:0in 0in 0in 4.0pt;border-color:currentcolor currentcolor currentcolor blue;border-image: none">
<div>
<div style="border:none;border-top:solid windowtext 1.0pt;padding:3.0pt 0in 0in 0in;border-color:currentcolor currentcolor;border-image: none">
<div>
<p class="MsoNormal"><b>From:</b><span class="apple-converted-space"> </span>Ni, Ray <<a href="mailto:ray.ni@intel.com">ray.ni@intel.com</a>><span class="apple-converted-space"> </span><br>
<b>Sent:</b><span class="apple-converted-space"> </span>Thursday, May 18, 2023 3:00 AM<br>
<b>To:</b><span class="apple-converted-space"> </span><a href="mailto:devel@edk2.groups.io">devel@edk2.groups.io</a><br>
<b>Cc:</b><span class="apple-converted-space"> </span>Kinney, Michael D <<a href="mailto:michael.d.kinney@intel.com">michael.d.kinney@intel.com</a>>; Rebecca Cran <<a href="mailto:rebecca@bsdio.com">rebecca@bsdio.com</a>>; Ni, Ray <<a href="mailto:ray.ni@intel.com">ray.ni@intel.com</a>><br>
<b>Subject:</b><span class="apple-converted-space"> </span>CpuDeadLoop() is optimized by compiler<o:p></o:p></p>
</div>
</div>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Hi,<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Starting from certain version of Visual Studio C compiler (I don’t have the exact version. I am using VS2019), CpuDeadLoop is now optimized quite well by compiler.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">The optimization is so “good” that it becomes harder for developers to break out of the deadloop.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">I copied the assembly instructions as below for your reference.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">The compiler does not generate instructions that jump out of the loop when the Index is not zero.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">So in order to break out of the loop, developers need to:<o:p></o:p></p>
</div>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-top:0in;margin-bottom:0in;mso-list:l0 level1 lfo1">
Manually adjust rsp by increasing 40<o:p></o:p></li><li class="MsoListParagraph" style="margin-top:0in;margin-bottom:0in;mso-list:l0 level1 lfo1">
Manually “ret”<o:p></o:p></li></ol>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">I am not sure if anyone has interest to re-write this function so that compiler can be “fooled” again.<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Thanks,<br>
Ray<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">=======================<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; Function compile flags: /Ogspy<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; File e:\work\edk2\MdePkg\Library\BaseLib\CpuDeadLoop.c<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; COMDAT CpuDeadLoop<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">_TEXT SEGMENT<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">Index$ = 48<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">CpuDeadLoop PROC ; COMDAT<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; 26 : {<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">$LN12:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 00000 48 83 ec 28 sub rsp, 40 ; 00000028H<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; 27 : volatile UINTN Index;<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; 28 :<span class="apple-converted-space"> </span><o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; 29 : for (Index = 0; Index == 0;) {<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 00004 48 c7 44 24 30<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 00 00 00 00 mov QWORD PTR Index$[rsp], 0<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">$LN10@CpuDeadLoo:<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">; 30 : CpuPause ();<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 0000d 48 8b 44 24 30 mov rax, QWORD PTR Index$[rsp]<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 00012 e8 00 00 00 00 call CpuPause<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> 00017 eb f4 jmp SHORT $LN10@CpuDeadLoo<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">CpuDeadLoop ENDP<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">_TEXT ENDS<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal">END<o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
<div>
<p class="MsoNormal"> <o:p></o:p></p>
</div>
</div>
<div>
<p class="MsoNormal"></o:p></span></p>
</div>
</div>
</blockquote>
</div>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
</div>
</div>
</body>
</html>
<div width="1" style="color:white;clear:both">_._,_._,_</div>
<hr>
Groups.io Links:<p>
You receive all messages sent to this group.
<p>
<a target="_blank" href="https://edk2.groups.io/g/devel/message/105040">View/Reply Online (#105040)</a> |
|
<a target="_blank" href="https://groups.io/mt/98987896/1813853">Mute This Topic</a>
| <a href="https://edk2.groups.io/g/devel/post">New Topic</a><br>
<a href="https://edk2.groups.io/g/devel/editsub/1813853">Your Subscription</a> |
<a href="mailto:devel+owner@edk2.groups.io">Contact Group Owner</a> |
<a href="https://edk2.groups.io/g/devel/leave/3943202/1813853/130120423/xyzzy">Unsubscribe</a>
[edk2-devel-archive@redhat.com]<br>
<div width="1" style="color:white;clear:both">_._,_._,_</div>