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diff --git a/share/doc/gdb/Agent-Expressions.html b/share/doc/gdb/Agent-Expressions.html new file mode 100644 index 0000000..0652ae2 --- /dev/null +++ b/share/doc/gdb/Agent-Expressions.html @@ -0,0 +1,136 @@ +<!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 "Free Software" and "Free Software Needs +Free Documentation", with the Front-Cover Texts being "A GNU Manual," +and with the Back-Cover Texts as in (a) below. + +(a) The FSF's Back-Cover Text is: "You are free to copy and modify +this GNU Manual. Buying copies from GNU Press supports the FSF in +developing GNU and promoting software freedom." --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Agent Expressions</title> + +<meta name="description" content="Debugging with GDB: Agent Expressions"> +<meta name="keywords" content="Debugging with GDB: Agent Expressions"> +<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="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="index.html#Top" rel="up" title="Top"> +<link href="General-Bytecode-Design.html#General-Bytecode-Design" rel="next" title="General Bytecode Design"> +<link href="Branch-Trace-Configuration-Format.html#Branch-Trace-Configuration-Format" rel="previous" title="Branch Trace Configuration Format"> +<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="Agent-Expressions"></a> +<div class="header"> +<p> +Next: <a href="Target-Descriptions.html#Target-Descriptions" accesskey="n" rel="next">Target Descriptions</a>, Previous: <a href="Remote-Protocol.html#Remote-Protocol" accesskey="p" rel="previous">Remote Protocol</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="The-GDB-Agent-Expression-Mechanism"></a> +<h2 class="appendix">Appendix F The GDB Agent Expression Mechanism</h2> + +<p>In some applications, it is not feasible for the debugger to interrupt +the program’s execution long enough for the developer to learn anything +helpful about its behavior. If the program’s correctness depends on its +real-time behavior, delays introduced by a debugger might cause the +program to fail, even when the code itself is correct. It is useful to +be able to observe the program’s behavior without interrupting it. +</p> +<p>Using GDB’s <code>trace</code> and <code>collect</code> commands, the user can +specify locations in the program, and arbitrary expressions to evaluate +when those locations are reached. Later, using the <code>tfind</code> +command, she can examine the values those expressions had when the +program hit the trace points. The expressions may also denote objects +in memory — structures or arrays, for example — whose values GDB +should record; while visiting a particular tracepoint, the user may +inspect those objects as if they were in memory at that moment. +However, because GDB records these values without interacting with the +user, it can do so quickly and unobtrusively, hopefully not disturbing +the program’s behavior. +</p> +<p>When GDB is debugging a remote target, the GDB <em>agent</em> code running +on the target computes the values of the expressions itself. To avoid +having a full symbolic expression evaluator on the agent, GDB translates +expressions in the source language into a simpler bytecode language, and +then sends the bytecode to the agent; the agent then executes the +bytecode, and records the values for GDB to retrieve later. +</p> +<p>The bytecode language is simple; there are forty-odd opcodes, the bulk +of which are the usual vocabulary of C operands (addition, subtraction, +shifts, and so on) and various sizes of literals and memory reference +operations. The bytecode interpreter operates strictly on machine-level +values — various sizes of integers and floating point numbers — and +requires no information about types or symbols; thus, the interpreter’s +internal data structures are simple, and each bytecode requires only a +few native machine instructions to implement it. The interpreter is +small, and strict limits on the memory and time required to evaluate an +expression are easy to determine, making it suitable for use by the +debugging agent in real-time applications. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="General-Bytecode-Design.html#General-Bytecode-Design" accesskey="1">General Bytecode Design</a>:</td><td> </td><td align="left" valign="top">Overview of the interpreter. +</td></tr> +<tr><td align="left" valign="top">• <a href="Bytecode-Descriptions.html#Bytecode-Descriptions" accesskey="2">Bytecode Descriptions</a>:</td><td> </td><td align="left" valign="top">What each one does. +</td></tr> +<tr><td align="left" valign="top">• <a href="Using-Agent-Expressions.html#Using-Agent-Expressions" accesskey="3">Using Agent Expressions</a>:</td><td> </td><td align="left" valign="top">How agent expressions fit into the big picture. +</td></tr> +<tr><td align="left" valign="top">• <a href="Varying-Target-Capabilities.html#Varying-Target-Capabilities" accesskey="4">Varying Target Capabilities</a>:</td><td> </td><td align="left" valign="top">How to discover what the target can do. +</td></tr> +<tr><td align="left" valign="top">• <a href="Rationale.html#Rationale" accesskey="5">Rationale</a>:</td><td> </td><td align="left" valign="top">Why we did it this way. +</td></tr> +</table> + + + + +<hr> +<div class="header"> +<p> +Next: <a href="Target-Descriptions.html#Target-Descriptions" accesskey="n" rel="next">Target Descriptions</a>, Previous: <a href="Remote-Protocol.html#Remote-Protocol" accesskey="p" rel="previous">Remote Protocol</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |