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diff --git a/share/doc/gcc/C_002b_002b-Compiled-Module-Interface.html b/share/doc/gcc/C_002b_002b-Compiled-Module-Interface.html new file mode 100644 index 0000000..25d8fae --- /dev/null +++ b/share/doc/gcc/C_002b_002b-Compiled-Module-Interface.html @@ -0,0 +1,172 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. Copies published by the Free Software Foundation raise + funds for GNU development. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): C++ Compiled Module Interface</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): C++ Compiled Module Interface"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): C++ Compiled Module Interface"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C_002b_002b-Modules.html#C_002b_002b-Modules" rel="up" title="C++ Modules"> +<link href="C-Implementation.html#C-Implementation" rel="next" title="C Implementation"> +<link href="C_002b_002b-Module-Preprocessing.html#C_002b_002b-Module-Preprocessing" rel="previous" title="C++ Module Preprocessing"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="C_002b_002b-Compiled-Module-Interface"></a> +<div class="header"> +<p> +Previous: <a href="C_002b_002b-Module-Preprocessing.html#C_002b_002b-Module-Preprocessing" accesskey="p" rel="previous">C++ Module Preprocessing</a>, Up: <a href="C_002b_002b-Modules.html#C_002b_002b-Modules" accesskey="u" rel="up">C++ Modules</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="Compiled-Module-Interface"></a> +<h4 class="subsection">3.23.3 Compiled Module Interface</h4> +<a name="index-C_002b_002b-Compiled-Module-Interface"></a> + +<p>CMIs are an additional artifact when compiling named module +interfaces, partitions or header units. These are read when +importing. CMI contents are implementation-specific, and in GCC’s +case tied to the compiler version. Consider them a rebuildable cache +artifact, not a distributable object. +</p> +<p>When creating an output CMI, any missing directory components are +created in a manner that is safe for concurrent builds creating +multiple, different, CMIs within a common subdirectory tree. +</p> +<p>CMI contents are written to a temporary file, which is then atomically +renamed. Observers either see old contents (if there is an +existing file), or complete new contents. They do not observe the +CMI during its creation. This is unlike object file writing, which +may be observed by an external process. +</p> +<p>CMIs are read in lazily, if the host OS provides <code>mmap</code> +functionality. Generally blocks are read when name lookup or template +instantiation occurs. To inhibit this, the <samp>-fno-module-lazy</samp> +option may be used. +</p> +<p>The <samp>--param lazy-modules=<var>n</var></samp> parameter controls the limit +on the number of concurrently open module files during lazy loading. +Should more modules be imported, an LRU algorithm is used to determine +which files to close—until that file is needed again. This limit +may be exceeded with deep module dependency hierarchies. With large +code bases there may be more imports than the process limit of file +descriptors. By default, the limit is a few less than the per-process +file descriptor hard limit, if that is determinable.<a name="DOCF3" href="#FOOT3"><sup>3</sup></a> +</p> +<p>GCC CMIs use ELF32 as an architecture-neutral encapsulation mechanism. +You may use <code>readelf</code> to inspect them, although section +contents are largely undecipherable. There is a section named +<code>.gnu.c++.README</code>, which contains human-readable text. Other +than the first line, each line consists of <code><var>tag</var>: <code>value</code></code> +tuples. +</p> +<div class="smallexample"> +<pre class="smallexample">> <code>readelf -p.gnu.c++.README gcm.cache/foo.gcm</code> + +String dump of section '.gnu.c++.README': + [ 0] GNU C++ primary module interface + [ 21] compiler: 11.0.0 20201116 (experimental) [c++-modules revision 20201116-0454] + [ 6f] version: 2020/11/16-04:54 + [ 89] module: foo + [ 95] source: c_b.ii + [ a4] dialect: C++20/coroutines + [ be] cwd: /data/users/nathans/modules/obj/x86_64/gcc + [ ee] repository: gcm.cache + [ 104] buildtime: 2020/11/16 15:03:21 UTC + [ 127] localtime: 2020/11/16 07:03:21 PST + [ 14a] export: foo:part1 foo-part1.gcm +</pre></div> + +<p>Amongst other things, this lists the source that was built, C++ +dialect used and imports of the module.<a name="DOCF4" href="#FOOT4"><sup>4</sup></a> The timestamp is the same value as that +provided by the <code>__DATE__</code> & <code>__TIME__</code> macros, and may be +explicitly specified with the environment variable +<code>SOURCE_DATE_EPOCH</code>. For further details +see <a href="Environment-Variables.html#Environment-Variables">Environment Variables</a>. +</p> +<p>A set of related CMIs may be copied, provided the relative pathnames +are preserved. +</p> +<p>The <code>.gnu.c++.README</code> contents do not affect CMI integrity, and +it may be removed or altered. The section numbering of the sections +whose names do not begin with <code>.gnu.c++.</code>, or are not the string +section is significant and must not be altered. +</p> +<div class="footnote"> +<hr> +<h4 class="footnotes-heading">Footnotes</h4> + +<h3><a name="FOOT3" href="#DOCF3">(3)</a></h3> +<p>Where +applicable the soft limit is incremented as needed towards the hard limit.</p> +<h3><a name="FOOT4" href="#DOCF4">(4)</a></h3> +<p>The precise contents +of this output may change.</p> +</div> +<hr> +<div class="header"> +<p> +Previous: <a href="C_002b_002b-Module-Preprocessing.html#C_002b_002b-Module-Preprocessing" accesskey="p" rel="previous">C++ Module Preprocessing</a>, Up: <a href="C_002b_002b-Modules.html#C_002b_002b-Modules" accesskey="u" rel="up">C++ Modules</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |