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4.3 KiB
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85 lines
4.3 KiB
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<title>JIT Interface - Debugging with GDB</title>
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<a name="JIT-Interface"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="In_002dProcess-Agent.html#In_002dProcess-Agent">In-Process Agent</a>,
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</div>
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<h2 class="chapter">29 JIT Compilation Interface</h2>
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<p><a name="index-just_002din_002dtime-compilation-3150"></a><a name="index-JIT-compilation-interface-3151"></a>
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This chapter documents <span class="sc">gdb</span>'s <dfn>just-in-time</dfn> (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>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 <span class="sc">gdb</span> 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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<span class="sc">gdb</span> has an interface that allows the program to register in-memory
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symbol files with <span class="sc">gdb</span> at runtime.
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<p>If you are using <span class="sc">gdb</span> 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>Broadly speaking, the JIT interface mirrors the dynamic loader interface. The
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JIT compiler communicates with <span class="sc">gdb</span> by writing data into a global
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variable and calling a fuction at a well-known symbol. When <span class="sc">gdb</span>
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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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<ul class="menu">
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<li><a accesskey="1" href="Declarations.html#Declarations">Declarations</a>: Relevant C struct declarations
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<li><a accesskey="2" href="Registering-Code.html#Registering-Code">Registering Code</a>: Steps to register code
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<li><a accesskey="3" href="Unregistering-Code.html#Unregistering-Code">Unregistering Code</a>: Steps to unregister code
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<li><a accesskey="4" href="Custom-Debug-Info.html#Custom-Debug-Info">Custom Debug Info</a>: Emit debug information in a custom format
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</ul>
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</body></html>
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