[llvm-c] Expose getFunctionAddress, as a modern alternative

[artagnon]

Summary

The OCaml bindings use getPointerToGlobal as the primary way to get a
handle on functions to run. This function is broken and deprecated, and
we want to transition to the modern getFunctionAddress alternative. This
is a two step process: first, there needs to be a C wrapper that OCaml
can leverage. So, build LLVMGetFunctionAddress with a test.

Second, there needs to be an OCaml interface to the new
LLVMGetFunctionAddress C function. This will be done in another patch.

[whitequark]

Since getPointerToGlobal was equivalent to getGlobalValueAddress, you should at least expose both getGlobalValueAddress and getFunctionAddress.

lib/ExecutionEngine/ExecutionEngineBindings.cpp

332

Is this really necessary?

"Clients that intend to execute code locally can use the getFunctionAddress call, which will generate code and apply final preparations all in one step."

[artagnon]

Respond to whitequark's review:

1. Remove the unnecessary finalizeObject() call.
2. Wrap getGlobalValueAddress() as well.

[whitequark]

Committed as rL224720

include/llvm-c/ExecutionEngine.h

 LLVMTargetMachineRef
 LLVMGetExecutionEngineTargetMachine(LLVMExecutionEngineRef EE);
 
 void LLVMAddGlobalMapping(LLVMExecutionEngineRef EE, LLVMValueRef Global,
                           void* Addr);
 
 void *LLVMGetPointerToGlobal(LLVMExecutionEngineRef EE, LLVMValueRef Global);
 
+uint64_t LLVMGetGlobalValueAddress(LLVMExecutionEngineRef EE, const char *Name);
+
+uint64_t LLVMGetFunctionAddress(LLVMExecutionEngineRef EE, const char *Name);
+
 /*===-- Operations on memory managers -------------------------------------===*/
 
 typedef uint8_t *(*LLVMMemoryManagerAllocateCodeSectionCallback)(
   void *Opaque, uintptr_t Size, unsigned Alignment, unsigned SectionID,
   const char *SectionName);
 typedef uint8_t *(*LLVMMemoryManagerAllocateDataSectionCallback)(
   void *Opaque, uintptr_t Size, unsigned Alignment, unsigned SectionID,
   const char *SectionName, LLVMBool IsReadOnly);

lib/ExecutionEngine/ExecutionEngineBindings.cpp

 }
 
 void *LLVMGetPointerToGlobal(LLVMExecutionEngineRef EE, LLVMValueRef Global) {
   unwrap(EE)->finalizeObject();
   
   return unwrap(EE)->getPointerToGlobal(unwrap<GlobalValue>(Global));
 }
 
+uint64_t LLVMGetGlobalValueAddress(LLVMExecutionEngineRef EE, const char *Name) {
+  return unwrap(EE)->getGlobalValueAddress(Name);
+}
+
+uint64_t LLVMGetFunctionAddress(LLVMExecutionEngineRef EE, const char *Name) {
+  return unwrap(EE)->getFunctionAddress(Name);
+}
+
 /*===-- Operations on memory managers -------------------------------------===*/
 
 namespace {
 
 struct SimpleBindingMMFunctions {
   LLVMMemoryManagerAllocateCodeSectionCallback AllocateCodeSection;
   LLVMMemoryManagerAllocateDataSectionCallback AllocateDataSection;
   LLVMMemoryManagerFinalizeMemoryCallback FinalizeMemory;

unittests/ExecutionEngine/MCJIT/MCJITCAPITest.cpp

union {
     void *raw;
     int (*usable)();
   } functionPointer;
   functionPointer.raw = LLVMGetPointerToGlobal(Engine, Function);
   
   EXPECT_EQ(42, functionPointer.usable());
 }
 
+TEST_F(MCJITCAPITest, gva) {
+  SKIP_UNSUPPORTED_PLATFORM;
+
+  Module = LLVMModuleCreateWithName("simple_module");
+  LLVMSetTarget(Module, HostTriple.c_str());
+  LLVMValueRef GlobalVar = LLVMAddGlobal(Module, LLVMInt32Type(), "simple_value");
+  LLVMSetInitializer(GlobalVar, LLVMConstInt(LLVMInt32Type(), 42, 0));
+
+  buildMCJITOptions();
+  buildMCJITEngine();
+  buildAndRunPasses();
+
+  union {
+    uint64_t raw;
+    int32_t *usable;
+  } valuePointer;
+  valuePointer.raw = LLVMGetGlobalValueAddress(Engine, "simple_value");
+
+  EXPECT_EQ(42, *valuePointer.usable);
+}
+
+TEST_F(MCJITCAPITest, gfa) {
+  SKIP_UNSUPPORTED_PLATFORM;
+
+  buildSimpleFunction();
+  buildMCJITOptions();
+  buildMCJITEngine();
+  buildAndRunPasses();
+
+  union {
+    uint64_t raw;
+    int (*usable)();
+  } functionPointer;
+  functionPointer.raw = LLVMGetFunctionAddress(Engine, "simple_function");
+
+  EXPECT_EQ(42, functionPointer.usable());
+}
+
 TEST_F(MCJITCAPITest, custom_memory_manager) {
   SKIP_UNSUPPORTED_PLATFORM;
   
   buildSimpleFunction();
   buildMCJITOptions();
   useRoundTripSectionMemoryManager();
   buildMCJITEngine();
   buildAndRunPasses();