Newbie question: Getting info about JIT-compiled function

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1

Apologies if this is a FAQ.

I am using the LLVM JIT facility on an x86_64 platform. I generate IR for a single function using IRBuilder(), use the FunctionPassManager to do some optimization passes, and then call ExecutionEngine::getPointerToFunction() to get a native-code version of the function. Everything works fine so far.

Two questions:

Question (1): How can I get the size of the native function? I see that the information is stored in the __jitSymbolTable structure in JITEmitter.cpp, but I don't see any interface to query this symbol table. I see AddFunctionToSymbolTable() and RemoveFunctionFromSymbolTable(), but not any equivalent of GetFunctionFromSymbolTable(). Is there a supported way to get at the JitSymbolEntry for a function? If not, is there an alternate way to determine the size (in bytes) of the native function?

Question (2): Does LLVM have any routines for printing the disassembly of a native code function? I see that lli can do this, but I would much prefer an LLVM library routine that I can call from my own code rather than having to write the bitcode to a file and then invoke lli. Suggestions?

Thanks for any help!

-- Jeff Kuskin

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Jeff Kuskin wrote:

Apologies if this is a FAQ.

I am using the LLVM JIT facility on an x86_64 platform. I generate
IR for a single function using IRBuilder(), use the
FunctionPassManager to do some optimization passes, and then call
ExecutionEngine::getPointerToFunction() to get a native-code version
of the function. Everything works fine so far.

Two questions:

Question (1): How can I get the size of the native function? I see
that the information is stored in the __jitSymbolTable structure in
JITEmitter.cpp, but I don't see any interface to query this symbol
table. I see AddFunctionToSymbolTable() and
RemoveFunctionFromSymbolTable(), but not any equivalent of
GetFunctionFromSymbolTable(). Is there a supported way to get at
the JitSymbolEntry for a function? If not, is there an alternate
way to determine the size (in bytes) of the native function?

The answer seems to be "create your own memory manager and define
endFunctionBody()". If you have a look at class MyJITMemoryManager in
http://icedtea.classpath.org/hg/icedtea6/file/0507a324ec22/ports/hotspot/src/share/vm/shark/sharkBuilder.hpp
you'll see how I did it.

Question (2): Does LLVM have any routines for printing the
disassembly of a native code function? I see that lli can do this,
but I would much prefer an LLVM library routine that I can call from
my own code rather than having to write the bitcode to a file and
then invoke lli. Suggestions?

This keeps changing, but on x86 with 4.2 you do this to enable assembly
dumps:

std::vector<const char*> Args;
Args.push_back(""); // program name
Args.push_back("-debug-only=" "x86-emitter");
cl::ParseCommandLineOptions(Args.size()-1, (char**)&Args[0]);

Andrew.