[llvm] r191030 - llvm-c: Add LLVMGetPointerToFunction

[Eric Christopher]

On Thu, Sep 19, 2013 at 1:54 PM, Filip Pizlo <fpizlo at apple.com> wrote:
>
>
> 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.
>

Didn't figure so :)

That said, I think Jim is correct about the way we'd like that
function to look externally or how it should work.

-eric

> -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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