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diff --git a/share/doc/gccint/LTO-object-file-layout.html b/share/doc/gccint/LTO-object-file-layout.html new file mode 100644 index 0000000..ef41205 --- /dev/null +++ b/share/doc/gccint/LTO-object-file-layout.html @@ -0,0 +1,197 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- 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>GNU Compiler Collection (GCC) Internals: LTO object file layout</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: LTO object file layout"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: LTO object file layout"> +<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="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="LTO.html#LTO" rel="up" title="LTO"> +<link href="IPA.html#IPA" rel="next" title="IPA"> +<link href="LTO-Overview.html#LTO-Overview" rel="previous" title="LTO Overview"> +<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" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="LTO-object-file-layout"></a> +<div class="header"> +<p> +Next: <a href="IPA.html#IPA" accesskey="n" rel="next">IPA</a>, Previous: <a href="LTO-Overview.html#LTO-Overview" accesskey="p" rel="previous">LTO Overview</a>, Up: <a href="LTO.html#LTO" accesskey="u" rel="up">LTO</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="LTO-file-sections"></a> +<h3 class="section">25.2 LTO file sections</h3> + +<p>LTO information is stored in several ELF sections inside object files. +Data structures and enum codes for sections are defined in +<samp>lto-streamer.h</samp>. +</p> +<p>These sections are emitted from <samp>lto-streamer-out.cc</samp> and mapped +in all at once from <samp>lto/lto.cc</samp>:<code>lto_file_read</code>. The +individual functions dealing with the reading/writing of each section +are described below. +</p> +<ul> +<li> Command line options (<code>.gnu.lto_.opts</code>) + +<p>This section contains the command line options used to generate the +object files. This is used at link time to determine the optimization +level and other settings when they are not explicitly specified at the +linker command line. +</p> +<p>Most options are recorded at a per function level and their setting +restored when processing the functions at link time. Global options +are composed from options specified at compile time and link time. +How exactly they are combined or mismatches diagnosed is implemented in +<samp>lto-wrapper.cc</samp>:<code>find_and_merge_options</code>. +</p> + +</li><li> Symbol table (<code>.gnu.lto_.symtab</code>) + +<p>This table replaces the ELF symbol table for functions and variables +represented in the LTO IL. Symbols used and exported by the optimized +assembly code of “fat” objects might not match the ones used and +exported by the intermediate code. This table is necessary because +the intermediate code is less optimized and thus requires a separate +symbol table. +</p> +<p>Additionally, the binary code in the “fat” object will lack a call +to a function, since the call was optimized out at compilation time +after the intermediate language was streamed out. In some special +cases, the same optimization may not happen during link-time +optimization. This would lead to an undefined symbol if only one +symbol table was used. +</p> +<p>The symbol table is emitted in +<samp>lto-streamer-out.cc</samp>:<code>produce_symtab</code>. +</p> + +</li><li> Global declarations and types (<code>.gnu.lto_.decls</code>) + +<p>This section contains an intermediate language dump of all +declarations and types required to represent the callgraph, static +variables and top-level debug info. +</p> +<p>The contents of this section are emitted in +<samp>lto-streamer-out.cc</samp>:<code>produce_asm_for_decls</code>. Types and +symbols are emitted in a topological order that preserves the sharing +of pointers when the file is read back in +(<samp>lto.cc</samp>:<code>read_cgraph_and_symbols</code>). +</p> + +</li><li> The callgraph (<code>.gnu.lto_.cgraph</code>) + +<p>This section contains the basic data structure used by the GCC +inter-procedural optimization infrastructure. This section stores an +annotated multi-graph which represents the functions and call sites as +well as the variables, aliases and top-level <code>asm</code> statements. +</p> +<p>This section is emitted in +<samp>lto-streamer-out.cc</samp>:<code>output_cgraph</code> and read in +<samp>lto-cgraph.cc</samp>:<code>input_cgraph</code>. +</p> + +</li><li> IPA references (<code>.gnu.lto_.refs</code>) + +<p>This section contains references between function and static +variables. It is emitted by <samp>lto-cgraph.cc</samp>:<code>output_refs</code> +and read by <samp>lto-cgraph.cc</samp>:<code>input_refs</code>. +</p> + +</li><li> Function bodies (<code>.gnu.lto_.function_body.<name></code>) + +<p>This section contains function bodies in the intermediate language +representation. Every function body is in a separate section to allow +copying of the section independently to different object files or +reading the function on demand. +</p> +<p>Functions are emitted in +<samp>lto-streamer-out.cc</samp>:<code>output_function</code> and read in +<samp>lto-streamer-in.cc</samp>:<code>input_function</code>. +</p> + +</li><li> Static variable initializers (<code>.gnu.lto_.vars</code>) + +<p>This section contains all the symbols in the global variable pool. It +is emitted by <samp>lto-cgraph.cc</samp>:<code>output_varpool</code> and read in +<samp>lto-cgraph.cc</samp>:<code>input_cgraph</code>. +</p> +</li><li> Summaries and optimization summaries used by IPA passes +(<code>.gnu.lto_.<xxx></code>, where <code><xxx></code> is one of <code>jmpfuncs</code>, +<code>pureconst</code> or <code>reference</code>) + +<p>These sections are used by IPA passes that need to emit summary +information during LTO generation to be read and aggregated at +link time. Each pass is responsible for implementing two pass manager +hooks: one for writing the summary and another for reading it in. The +format of these sections is entirely up to each individual pass. The +only requirement is that the writer and reader hooks agree on the +format. +</p></li></ul> + + +<hr> +<div class="header"> +<p> +Next: <a href="IPA.html#IPA" accesskey="n" rel="next">IPA</a>, Previous: <a href="LTO-Overview.html#LTO-Overview" accesskey="p" rel="previous">LTO Overview</a>, Up: <a href="LTO.html#LTO" accesskey="u" rel="up">LTO</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |