reflect: use abi.FuncPCABIInternal

Use abi.FuncPCABIInternal instead of going through assembly or
unsafe.Pointer hacks.

For golang#38783

src/reflect/asm_amd64.s

@@ -82,7 +82,7 @@ TEXT ·methodValueCall(SB),(NOSPLIT|WRAPPER),$312
 // at any of the initial call instructions. The entry point is used to determine
 // the closure which implements the method.
 // No preamble of any kind, we need to do things manually.
-TEXT ·dispatchToMethod(SB),(NOSPLIT|NOFRAME),$0-0
+TEXT ·dispatchToMethod<ABIInternal>(SB),(NOSPLIT|NOFRAME),$0-0
 	CALL ·dispatchLabel(SB)
 	CALL ·dispatchLabel(SB)
 	CALL ·dispatchLabel(SB)
@@ -913,10 +913,3 @@ TEXT ·dispatchLabel(SB),(NOSPLIT|NOFRAME),$0-0
 	// Currently, (DX) is always makeFuncStub, but this method of dispatch
 	// might have other clients in the future, so we leave the indirect jump in.
 	JMP (DX)
-
-// getDispatchToMethodAddr simply returns the address of the actual code of
-// dispatchToMethod. This needs to be in ASM since trying to get the address
-// from Go yields the address ABI conversion wrapper instead.
-TEXT ·getDispatchToMethodAddr<ABIInternal>(SB),(NOSPLIT|NOFRAME),$0-0
-	MOVQ $·dispatchToMethod(SB), AX
-	RET

src/reflect/makefunc.go

@@ -195,13 +195,8 @@ func dispatchToMethod()
 // assembly used in the implementation of dispatchToMethod.
 func dispatchLabel()
 
-// getDispatchToMethodAddr returns the address of the actual code of
-// dispatchToMethod. This must happen in ASM to obtain the correct
-// address independet of the used ABI.
-func getDispatchToMethodAddr() uintptr
-
 // dispatchToMethodAddr is the address of the actual code of dispatchToMethod.
-var dispatchToMethodAddr = getDispatchToMethodAddr()
+var dispatchToMethodAddr = abi.FuncPCABIInternal(dispatchToMethod)
 
 // currentMethodKey is the most recent method key used for creating a method
 // at runtime. Initially, it's the actual code address of dispatchToMethod.
@@ -242,8 +237,7 @@ func allocMethodSlot(closure unsafe.Pointer) unsafe.Pointer {
 	newKey := atomic.AddUintptr(&currentMethodKey, dispatchStep)
 	if newKey > dispatchToMethodAddr+dispatchLimit {
 		atomic.AddUintptr(&currentMethodKey, ^uintptr(dispatchStep)+1)
-		dummy := methodSlotsExhausted
-		return unsafe.Pointer(**(**uintptr)(unsafe.Pointer(&dummy)))
+		return unsafe.Pointer(abi.FuncPCABIInternal(methodSlotsExhausted))
 	}
 	methodMap.Store(newKey, closure)
 	return unsafe.Pointer(newKey - dispatchStep)