1 files changed, 85 insertions, 0 deletions
diff --git a/src/Native/System.Private.TypeLoader.Native/amd64/ConstrainedCallSupportHelpers.asm b/src/Native/System.Private.TypeLoader.Native/amd64/ConstrainedCallSupportHelpers.asm
new file mode 100644
index 000000000..4d22d914c
--- /dev/null
+++ b/src/Native/System.Private.TypeLoader.Native/amd64/ConstrainedCallSupportHelpers.asm
@@ -0,0 +1,85 @@
+;; Licensed to the .NET Foundation under one or more agreements.
+;; The .NET Foundation licenses this file to you under the MIT license.
+;; See the LICENSE file in the project root for more information.
+
+;; -----------------------------------------------------------------------------------------------------------
+;; #include "asmmacros.inc"
+;; -----------------------------------------------------------------------------------------------------------
+
+LEAF_ENTRY macro Name, Section
+    Section segment para 'CODE'
+    align   16
+    public  Name
+    Name    proc
+endm
+
+LEAF_END macro Name, Section
+    Name    endp
+    Section ends
+endm
+
+;  - TAILCALL_RAX: ("jmp rax") should be used for tailcalls, this emits an instruction 
+;            sequence which is recognized by the unwinder as a valid epilogue terminator
+TAILJMP_RAX TEXTEQU <DB 048h, 0FFh, 0E0h>
+POINTER_SIZE                        equ 08h
+
+;;
+;; Note: The "__jmpstub__" prefix is used to indicate to debugger
+;; that it must step-through this stub when it encounters it while
+;; stepping.
+;;
+
+;;
+;; __jmpstub__ConstrainedCallSupport_DerefThisAndCall_CommonCallingStub
+;;
+;; r10 - AddressOfAddressOfFunctionToCallAfterDereferencingThis
+;;
+LEAF_ENTRY __jmpstub__ConstrainedCallSupport_DerefThisAndCall_CommonCallingStub, _TEXT
+        mov     rax, [r10]                ; Tail jumps go through RAX, so copy function pointer there
+        mov     rcx, [rcx]                ; Deference this to get real function pointer
+        TAILJMP_RAX
+LEAF_END __jmpstub__ConstrainedCallSupport_DerefThisAndCall_CommonCallingStub, _TEXT
+
+;;
+;; void ConstrainedCallSupport_GetStubs(IntPtr *__jmpstub__ConstrainedCallSupport_DerefThisAndCall_CommonCallingStub,
+;;                                      IntPtr *__jmpstub__ConstrainedCallSupport_DirectConstrainedCallCommonStub)
+;;
+LEAF_ENTRY ConstrainedCallSupport_GetStubs, _TEXT
+        lea     rax, [__jmpstub__ConstrainedCallSupport_DerefThisAndCall_CommonCallingStub]
+        mov    [rcx], rax
+        lea     rax, [__jmpstub__ConstrainedCallSupport_DirectConstrainedCallCommonStub]
+        mov    [rdx], rax
+        ret
+LEAF_END ConstrainedCallSupport_GetStubs, _TEXT
+
+;;
+;; __jmpstub__ConstrainedCallSupport_DirectConstrainedCallCommonStub
+;;
+;; struct ConstrainedCallDesc
+;; {
+;;     ULONG_PTR ExactTarget;
+;;     ULONG_PTR LookupFunc; // Put UniversalThunk here
+;; }
+;;
+;; struct CommonCallingStubInputData
+;; {
+;;     ULONG_PTR ConstrainedCallDesc;
+;;     ULONG_PTR DirectConstrainedCallResolver;
+;; }
+;;
+;; r10 - Points at CommonCallingStubInputData
+;;  
+;;
+LEAF_ENTRY __jmpstub__ConstrainedCallSupport_DirectConstrainedCallCommonStub, _TEXT
+        mov     r11, [r10]                ; put ConstrainedCallDesc into r11 (Arg to LookupFunc/Temp for getting ExactTarget)
+        mov     rax, [r11]                ; put ExactTarget into rax
+        test    rax, rax                  ; compare against null
+        jnz     JumpToTarget              ; if not null, we don't need to call helper to get result. Just jump
+        ; If we reach here, we need to use a universal thunk to call the LookupFunc
+        mov     rax, [r11 + POINTER_SIZE] ; Get Universal thunk function pointer into rax
+        mov     r10, [r10 + POINTER_SIZE] ; Put DirectConstrainedCallResolver into r10 for UniversalTransitionThunk call
+JumpToTarget:
+        TAILJMP_RAX
+LEAF_END __jmpstub__ConstrainedCallSupport_DirectConstrainedCallCommonStub, _TEXT
+
+end