[llvm] r191030 - llvm-c: Add LLVMGetPointerToFunction

[Filip Pizlo]

On Sep 19, 2013, at 1:47 PM, Eric Christopher <echristo at gmail.com> wrote:

> Very curious about RunFunction then?

What about it? ;-)

> 
> When I did the JIT aspect I used getPointerToFunction, what are you
> guys using at the moment in webkit-land?

LLVMGetPointerToGlobal().  We create an MCJIT, give it a module and then call LLVMGetPointerToGlobal(), passing it a Value that is the function we want.

There's other stuff going on, as well - like having a custom memory manager so that WebKit can control where/how all sections get allocated by Dyld.  But the basic workflow if you want to launch a local JIT to generate some code is (1) create the JIT with the module you want to compile, (2) get pointers to your functions with LLVMGetPointerToGlobal().  The latter also forces a compile.

It's true you can call RunFunction but this is silly for many JIT clients.  You will want to call the generated code directly, either from C or from other JITed code that you have generated. We don't use RunFunction, and don't ever intend to.

-Filip


> 
> -eric
> 
> On Thu, Sep 19, 2013 at 1:46 PM, Filip Pizlo <fpizlo at apple.com> wrote:
>> How is that different from LLVMGetPointerToGlobal()?
>> 
>> And I agree that this should work.  It's great that the JIT could be used
>> for remote execution, but some clients will never use the JIT in that
>> fashion.  They will just want a void*.
>> 
>> -Filip
>> 
>> 
>> On Sep 19, 2013, at 1:36 PM, Eric Christopher <echristo at gmail.com> wrote:
>> 
>> Hrm. That's a good point and one I hadn't thought about... what's the
>> best way forward here? There's definitely a useful need in getting a
>> void * to a function out of the JIT from the C level.
>> 
>> -eric
>> 
>> On Thu, Sep 19, 2013 at 1:30 PM, Jim Grosbach <grosbach at apple.com> wrote:
>> 
>> This isn’t going to work when the execution target isn’t local. The pointer
>> to the function is in the executing process address space and this returns a
>> pointer in the compiler’s address space.
>> 
>> That’s a fundamental problem with the old JIT, and is semi-baked into the
>> ExecutionEngine API, unfortunately, and cleaning that up is going to be
>> painful. We shouldn’t, however, make the problem worse.
>> 
>> -Jim
>> 
>> On Sep 19, 2013, at 12:55 PM, Anders Waldenborg <anders at 0x63.nu> wrote:
>> 
>> Author: andersg
>> Date: Thu Sep 19 14:55:06 2013
>> New Revision: 191030
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=191030&view=rev
>> Log:
>> llvm-c: Add LLVMGetPointerToFunction
>> 
>> Differential Revision: http://llvm-reviews.chandlerc.com/D1715
>> 
>> 
>> Modified:
>>  llvm/trunk/include/llvm-c/ExecutionEngine.h
>>  llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp
>> 
>> Modified: llvm/trunk/include/llvm-c/ExecutionEngine.h
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm-c/ExecutionEngine.h?rev=191030&r1=191029&r2=191030&view=diff
>> ==============================================================================
>> --- llvm/trunk/include/llvm-c/ExecutionEngine.h (original)
>> +++ llvm/trunk/include/llvm-c/ExecutionEngine.h Thu Sep 19 14:55:06 2013
>> @@ -141,6 +141,8 @@ LLVMGenericValueRef LLVMRunFunction(LLVM
>>                                   unsigned NumArgs,
>>                                   LLVMGenericValueRef *Args);
>> 
>> +void *LLVMGetPointerToFunction(LLVMExecutionEngineRef EE, LLVMValueRef F);
>> +
>> void LLVMFreeMachineCodeForFunction(LLVMExecutionEngineRef EE, LLVMValueRef
>> F);
>> 
>> void LLVMAddModule(LLVMExecutionEngineRef EE, LLVMModuleRef M);
>> 
>> Modified: llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp?rev=191030&r1=191029&r2=191030&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp (original)
>> +++ llvm/trunk/lib/ExecutionEngine/ExecutionEngineBindings.cpp Thu Sep 19
>> 14:55:06 2013
>> @@ -276,6 +276,10 @@ LLVMGenericValueRef LLVMRunFunction(LLVM
>> return wrap(Result);
>> }
>> 
>> +void *LLVMGetPointerToFunction(LLVMExecutionEngineRef EE, LLVMValueRef F) {
>> +  return unwrap(EE)->getPointerToFunction(unwrap<Function>(F));
>> +}
>> +
>> void LLVMFreeMachineCodeForFunction(LLVMExecutionEngineRef EE, LLVMValueRef
>> F) {
>> unwrap(EE)->freeMachineCodeForFunction(unwrap<Function>(F));
>> }
>> 
>> 
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