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