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;; 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.
.586
.model flat
option casemap:none
.code
include AsmMacros.inc
ifdef FEATURE_DYNAMIC_CODE
;;
;; Defines an assembly thunk used to make a transition from managed code to a callee,
;; then (based on the return value from the callee), either returning or jumping to
;; a new location while preserving the input arguments. The usage of this thunk also
;; ensures arguments passed are properly reported.
;;
;; TODO: This code currently only tailcalls, and does not return.
;;
;; Inputs:
;; ecx, edx, stack space three pops down: arguments as normal
;; first register sized fields on the stack is the location of the target code
;; the UniversalTransitionThunk will call
;; second register sized field on the stack is the parameter to the target function
;; followed by the return address of the whole method. (This method cannot be called
;; via a call instruction, it must be jumped to.) The fake entrypoint is in place to
;; convince the stack walker this is a normal framed function.
;;
;; NOTE! FOR CORRECTNESS THIS FUNCTION REQUIRES THAT ALL NON-LEAF MANAGED FUNCTIONS HAVE
;; FRAME POINTERS, OR THE STACK WALKER CAN'T STACKWALK OUT OF HERE
;;
;
; Frame layout is:
;
; {StackPassedArgs} ChildSP+018 CallerSP+000
; {CallerRetaddr} ChildSP+014 CallerSP-004
; {CallerEBP} ChildSP+010 CallerSP-008
; {ReturnBlock (0x8 bytes)} ChildSP+008 CallerSP-010
; -- On input (i.e., when control jumps to RhpUniversalTransition), the low 4 bytes of
; the ReturnBlock area holds the address of the callee and the high 4 bytes holds the
; extra argument to pass to the callee.
; {IntArgRegs (edx,ecx) (0x8 bytes)} ChildSP+000 CallerSP-018
; {CalleeRetaddr} ChildSP-004 CallerSP-01c
;
; NOTE: If the frame layout ever changes, the C++ UniversalTransitionStackFrame structure
; must be updated as well.
;
; NOTE: The callee receives a pointer to the base of the pushed IntArgRegs, and the callee
; has knowledge of the exact layout of the entire frame.
;
; NOTE: The stack walker guarantees that conservative GC reporting will be applied to
; everything between the base of the IntArgRegs and the top of the StackPassedArgs.
;
UNIVERSAL_TRANSITION macro FunctionName
FASTCALL_FUNC Rhp&FunctionName&_FAKE_ENTRY, 0
; Set up an ebp frame
push ebp
mov ebp, esp
push eax
push eax
ALTERNATE_ENTRY Rhp&FunctionName&@0
push ecx
push edx
;
; Call out to the target, while storing and reporting arguments to the GC.
;
mov eax, [ebp-8] ; Get the address of the callee
mov edx, [ebp-4] ; Get the extra argument to pass to the callee
lea ecx, [ebp-10h] ; Get pointer to edx value pushed above
call eax
EXPORT_POINTER_TO_ADDRESS _PointerToReturnFrom&FunctionName
; We cannot make the label public as that tricks DIA stackwalker into thinking
; it's the beginning of a method. For this reason we export an auxiliary variable
; holding the address instead.
pop edx
pop ecx
add esp, 8
pop ebp
jmp eax
FASTCALL_ENDFUNC
endm
; To enable proper step-in behavior in the debugger, we need to have two instances
; of the thunk. For the first one, the debugger steps into the call in the function,
; for the other, it steps over it.
UNIVERSAL_TRANSITION UniversalTransition
UNIVERSAL_TRANSITION UniversalTransition_DebugStepTailCall
endif
end
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