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<title>System Library</title>
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<div class="doc_title"> System Library</div>
<div class="doc_warning">Warning: This document is a work in progress.</div>
<ul>
<li><a href="#abstract">Abstract</a></li>
<li><a href="#requirements">System Library Requirements</a>
<ol>
<li><a href="#headers">Hide System Header Files</a></li>
<li><a href="#nofunc">No Exposed Functions</a></li>
<li><a href="#nodata">No Exposed Data</a></li>
<li><a href="#xcptns">No Exceptions</a></li>
<li><a href="#errors">Standard Error Codes</a></li>
<li><a href="#overhead">Minimize Overhead</a></li>
</ol></li>
<li><a href="#design">System Library Design</a>
<ol>
<li><a href="#opaque">Use Opaque Classes</a></li>
<li><a href="#common">Common Implementations</a></li>
<li><a href="#multi_imps">Multiple Implementations</a></li>
<li><a href="#lowlevel">Use Low Level Interfaces</a></li>
<li><a href="#memalloc">No Memory Allocation</a></li>
<li><a href="#virtuals">No Virtual Methods</a></li>
</ol></li>
<li><a href="#detail">System Library Details</a>
<ol>
<li><a href="#bug">Tracking Bugzilla Bug: 351</a></li>
<li><a href="#refimpl">Reference Implementatation</a></li>
</ol></li>
</ul>
<div class="doc_author">
<p>Written by the <a href="rspencer@x10sys.com">Reid Spencer</a></p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="abstract">Abstract</a></div>
<div class="doc_text">
<p>This document describes the requirements, design, and implementation
details of LLVM's System Library. The library is composed of the header files
in <tt>llvm/include/llvm/System</tt> and the source files in
<tt>llvm/lib/System</tt>. The goal of this library is to completely shield
LLVM from the variations in operating system interfaces. By centralizing
LLVM's use of operating system interfaces, we make it possible for the LLVM
tool chain and runtime libraries to be more easily ported to new platforms.
The library also unclutters the rest of LLVM from #ifdef use and special
cases for specific operating systems.</p>
<p>The System Library was donated to LLVM by Reid Spencer who formulated the
original design as part of the eXtensible Programming System (XPS) which is
based, in part, on LLVM.</p>
</div>
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<div class="doc_section">
<a name="requirements">System Library Requirements</a>
</div>
<div class="doc_text">
<p>The System library's requirements are aimed at shielding LLVM from the
variations in operating system interfaces. The following sections define the
requirements needed to fulfill this objective.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="headers">Hide System Header Files</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="nofunc">No Exposed Functions</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="nodata">No Exposed Data</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="xcptns">No Exceptions</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="errors">Standard Error Codes</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="overhead">Minimize Overhead</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="design">System Library Design</a></div>
<div class="doc_text">
<p>In order to fulfill the requirements of the system library, strict design
objectives must be maintained in the library as it evolves. The goal here
is to provide interfaces to operating system concepts (files, memory maps,
sockets, signals, locking, etc) efficiently and in such a way that the
remainder of LLVM is completely operating system agnostic.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="opaque">Use Opaque Classes</a></div>
<div class="doc_text">
<p>no public data</p>
<p>onlyprimitive typed private/protected data</p>
<p>data size is "right" for platform, not max of all platforms</p>
<p>each class corresponds to O/S concept</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="common">Common Implementations</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="multi_imps">Multiple Implementations</a>
</div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="low_level">Use Low Level Interfaces</a>
</div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="memalloc">No Memory Allocation</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="virtuals">No Virtual Methods</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section"><a name="detail">System Library Details</a></div>
<div class="doc_text">
<p>To be written.</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection"><a name="bug">Bug 251</a></div>
<div class="doc_text">
<p>See <a href="http://llvm.cs.uiuc.edu/bugs/show_bug?bug=351">bug 351</a>
for further details on the progress of this work</p>
</div>
<!-- ======================================================================= -->
<div class="doc_subsection">
<a name="refimpl">Reference Implementation</a>
</div>
<div class="doc_text">
<p>The <tt>linux</tt> implementation of the system library will always be the
reference implementation. This means that (a) the concepts defined by the
linux must be identically replicated in the other implementations and (b) the
linux implementation must always be complete (provide implementations for all
concepts).</p>
</div>
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<a href="mailto:rspencer@x10sys.com">Reid Spencer</a><br>
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