1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<!-- Copyright (C) 1988-2021 Free Software Foundation, Inc. 4 5Permission is granted to copy, distribute and/or modify this document 6under the terms of the GNU Free Documentation License, Version 1.3 or 7any later version published by the Free Software Foundation; with the 8Invariant Sections being "Free Software" and "Free Software Needs 9Free Documentation", with the Front-Cover Texts being "A GNU Manual," 10and with the Back-Cover Texts as in (a) below. 11 12(a) The FSF's Back-Cover Text is: "You are free to copy and modify 13this GNU Manual. 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A JIT compiler is a program or library that generates native 77executable code at runtime and executes it, usually in order to achieve good 78performance while maintaining platform independence. 79</p> 80<p>Programs that use JIT compilation are normally difficult to debug because 81portions of their code are generated at runtime, instead of being loaded from 82object files, which is where <small>GDB</small> normally finds the program’s symbols 83and debug information. In order to debug programs that use JIT compilation, 84<small>GDB</small> has an interface that allows the program to register in-memory 85symbol files with <small>GDB</small> at runtime. 86</p> 87<p>If you are using <small>GDB</small> to debug a program that uses this interface, then 88it should work transparently so long as you have not stripped the binary. If 89you are developing a JIT compiler, then the interface is documented in the rest 90of this chapter. At this time, the only known client of this interface is the 91LLVM JIT. 92</p> 93<p>Broadly speaking, the JIT interface mirrors the dynamic loader interface. The 94JIT compiler communicates with <small>GDB</small> by writing data into a global 95variable and calling a function at a well-known symbol. When <small>GDB</small> 96attaches, it reads a linked list of symbol files from the global variable to 97find existing code, and puts a breakpoint in the function so that it can find 98out about additional code. 99</p> 100<table class="menu" border="0" cellspacing="0"> 101<tr><td align="left" valign="top">• <a href="Declarations.html#Declarations" accesskey="1">Declarations</a>:</td><td> </td><td align="left" valign="top">Relevant C struct declarations 102</td></tr> 103<tr><td align="left" valign="top">• <a href="Registering-Code.html#Registering-Code" accesskey="2">Registering Code</a>:</td><td> </td><td align="left" valign="top">Steps to register code 104</td></tr> 105<tr><td align="left" valign="top">• <a href="Unregistering-Code.html#Unregistering-Code" accesskey="3">Unregistering Code</a>:</td><td> </td><td align="left" valign="top">Steps to unregister code 106</td></tr> 107<tr><td align="left" valign="top">• <a href="Custom-Debug-Info.html#Custom-Debug-Info" accesskey="4">Custom Debug Info</a>:</td><td> </td><td align="left" valign="top">Emit debug information in a custom format 108</td></tr> 109</table> 110 111<hr> 112<div class="header"> 113<p> 114Next: <a href="In_002dprocess-Agent.html#In_002dprocess-Agent" accesskey="n" rel="next">In-process Agent</a>, Previous: <a href="Annotations.html#Annotations" accesskey="p" rel="previous">Annotations</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> 115</div> 116 117 118 119</body> 120</html> 121