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<title>Debugging with GDB: JIT Interface</title>
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<a name="JIT-Interface"></a>
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<p>
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Next: <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>
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<a name="JIT-Compilation-Interface"></a>
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<h2 class="chapter">29 JIT Compilation Interface</h2>
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<a name="index-just_002din_002dtime-compilation"></a>
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<a name="index-JIT-compilation-interface"></a>
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<p>This chapter documents <small>GDB</small>’s <em>just-in-time</em> (JIT) compilation
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interface. A JIT compiler is a program or library that generates native
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executable code at runtime and executes it, usually in order to achieve good
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performance while maintaining platform independence.
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</p>
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<p>Programs that use JIT compilation are normally difficult to debug because
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portions of their code are generated at runtime, instead of being loaded from
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object files, which is where <small>GDB</small> normally finds the program’s symbols
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and debug information. In order to debug programs that use JIT compilation,
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<small>GDB</small> has an interface that allows the program to register in-memory
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symbol files with <small>GDB</small> at runtime.
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</p>
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<p>If you are using <small>GDB</small> to debug a program that uses this interface, then
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it should work transparently so long as you have not stripped the binary. If
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you are developing a JIT compiler, then the interface is documented in the rest
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of this chapter. At this time, the only known client of this interface is the
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LLVM JIT.
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</p>
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<p>Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
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JIT compiler communicates with <small>GDB</small> by writing data into a global
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variable and calling a function at a well-known symbol. When <small>GDB</small>
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attaches, it reads a linked list of symbol files from the global variable to
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find existing code, and puts a breakpoint in the function so that it can find
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out about additional code.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<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
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</td></tr>
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<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
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</td></tr>
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<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
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</td></tr>
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<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
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</td></tr>
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</table>
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<p>
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Next: <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>
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