MiscStubs.asm

;; Licensed to the .NET Foundation under one or more agreements.
;; The .NET Foundation licenses this file to you under the MIT license.

#include "AsmMacros.h"

    EXTERN memcpy
    EXTERN memcpyGCRefs
    EXTERN memcpyGCRefsWithWriteBarrier
    EXTERN memcpyAnyWithWriteBarrier
    EXTERN GetClasslibCCtorCheck

    TEXTAREA

;;
;; Checks whether the static class constructor for the type indicated by the context structure has been
;; executed yet. If not the classlib is called via their CheckStaticClassConstruction callback which will
;; execute the cctor and update the context to record this fact.
;;
;;  Input:
;;      x0 : Address of StaticClassConstructionContext structure
;;
;;  Output:
;;      All volatile registers and the condition codes may be trashed.
;;
    LEAF_ENTRY RhpCheckCctor

        ;; Check the m_initialized field of the context. The cctor has been run only if this equals 1 (the
        ;; initial state is 0 and the remaining values are reserved for classlib use). This check is
        ;; unsynchronized; if we go down the slow path and call the classlib then it is responsible for
        ;; synchronizing with other threads and re-checking the value.
        ldr     w12, [x0, #OFFSETOF__StaticClassConstructionContext__m_initialized]
        cmp     w12, #1
        bne     RhpCheckCctor__SlowPath
        ret
RhpCheckCctor__SlowPath
        mov     x1, x0
        b       RhpCheckCctor2 ; tail-call the check cctor helper that actually has an implementation to call
                               ; the cctor

    LEAF_END RhpCheckCctor

;;
;; Checks whether the static class constructor for the type indicated by the context structure has been
;; executed yet. If not the classlib is called via their CheckStaticClassConstruction callback which will
;; execute the cctor and update the context to record this fact.
;;
;;  Input:
;;      x0 : Value that must be preserved in this register across the cctor check.
;;      x1 : Address of StaticClassConstructionContext structure
;;
;;  Output:
;;      All volatile registers other than x0 may be trashed and the condition codes may also be trashed.
;;
    LEAF_ENTRY RhpCheckCctor2

        ;; Check the m_initialized field of the context. The cctor has been run only if this equals 1 (the
        ;; initial state is 0 and the remaining values are reserved for classlib use). This check is
        ;; unsynchronized; if we go down the slow path and call the classlib then it is responsible for
        ;; synchronizing with other threads and re-checking the value.
        ldr     w12, [x1, #OFFSETOF__StaticClassConstructionContext__m_initialized]
        cmp     w12, #1
        bne     RhpCheckCctor2__SlowPath
        ret

    LEAF_END RhpCheckCctor2

;;
;; Slow path helper for RhpCheckCctor.
;;
;;  Input:
;;      x0 : Value that must be preserved in this register across the cctor check.
;;      x1 : Address of StaticClassConstructionContext structure
;;
;;  Output:
;;      All volatile registers other than x0 may be trashed and the condition codes may also be trashed.
;;
    NESTED_ENTRY RhpCheckCctor2__SlowPath

        ;; Need to preserve x0, x1 and lr across helper call. fp is also pushed to keep the stack 16 byte aligned.
        PROLOG_SAVE_REG_PAIR fp, lr, #-0x20!
        stp     x0, x1, [sp, #0x10]

        ;; Call a C++ helper to retrieve the address of the classlib callback. The caller's return address is
        ;; passed as the argument to the helper; it's an address in the module and is used by the helper to
        ;; locate the classlib.
        mov     x0, lr
        bl      GetClasslibCCtorCheck

        ;; X0 now contains the address of the classlib method to call. The single argument is the context
        ;; structure address currently in stashed on the stack. Clean up and tail call to the classlib
        ;; callback so we're not on the stack should a GC occur (so we don't need to worry about transition
        ;; frames).
        mov     x12, x0
        ldp     x0, x1, [sp, #0x10]
        EPILOG_RESTORE_REG_PAIR fp, lr, #0x20!
        ;; tail-call the class lib cctor check function. This function is required to return its first
        ;; argument, so that x0 can be preserved.
        EPILOG_NOP br x12

    NESTED_END RhpCheckCctor__SlowPath2


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; void* RhpCopyMultibyteNoGCRefs(void*, void*, size_t)
;;
;; The purpose of this wrapper is to hoist the potential null reference exceptions of copying memory up to a place where
;; the stack unwinder and exception dispatch can properly transform the exception into a managed exception and dispatch
;; it to managed code.
;;

    LEAF_ENTRY    RhpCopyMultibyteNoGCRefs

        ; x0    dest
        ; x1    src
        ; x2    count

        cbz     x2, NothingToCopy_NoGCRefs  ; check for a zero-length copy

        ; Now check the dest and src pointers.  If they AV, the EH subsystem will recognize the address of the AV,
        ; unwind the frame, and fixup the stack to make it look like the (managed) caller AV'ed, which will be 
        ; translated to a managed exception as usual.
    ALTERNATE_ENTRY RhpCopyMultibyteNoGCRefsDestAVLocation
        ldrb    wzr, [x0]
    ALTERNATE_ENTRY RhpCopyMultibyteNoGCRefsSrcAVLocation
        ldrb    wzr, [x1]

        ; tail-call to plain-old-memcpy
        b       memcpy

NothingToCopy_NoGCRefs
        ; dest is already in x0
        ret

    LEAF_END


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; void* RhpCopyMultibyte(void*, void*, size_t)
;;
;; The purpose of this wrapper is to hoist the potential null reference exceptions of copying memory up to a place where
;; the stack unwinder and exception dispatch can properly transform the exception into a managed exception and dispatch
;; it to managed code.
;;

    LEAF_ENTRY    RhpCopyMultibyte

        ; x0    dest
        ; x1    src
        ; x2    count

        ; check for a zero-length copy
        cbz     x2, NothingToCopy_RhpCopyMultibyte

        ; Now check the dest and src pointers.  If they AV, the EH subsystem will recognize the address of the AV,
        ; unwind the frame, and fixup the stack to make it look like the (managed) caller AV'ed, which will be 
        ; translated to a managed exception as usual.
    ALTERNATE_ENTRY RhpCopyMultibyteDestAVLocation
        ldrb    wzr, [x0]
    ALTERNATE_ENTRY RhpCopyMultibyteSrcAVLocation
        ldrb    wzr, [x1]

        ; tail-call to the GC-safe memcpy implementation
        b       memcpyGCRefs

NothingToCopy_RhpCopyMultibyte
        ; dest is already still in x0
        ret

    LEAF_END

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; void* RhpCopyMultibyteWithWriteBarrier(void*, void*, size_t)
;;
;; The purpose of this wrapper is to hoist the potential null reference exceptions of copying memory up to a place where
;; the stack unwinder and exception dispatch can properly transform the exception into a managed exception and dispatch
;; it to managed code.
;; Runs a card table update via RhpBulkWriteBarrier after the copy
;;

    LEAF_ENTRY    RhpCopyMultibyteWithWriteBarrier

        ; x0    dest
        ; x1    src
        ; x2    count

        ; check for a zero-length copy
        cbz     x2, NothingToCopy_RhpCopyMultibyteWithWriteBarrier

        ; Now check the dest and src pointers.  If they AV, the EH subsystem will recognize the address of the AV,
        ; unwind the frame, and fixup the stack to make it look like the (managed) caller AV'ed, which will be 
        ; translated to a managed exception as usual.
    ALTERNATE_ENTRY RhpCopyMultibyteWithWriteBarrierDestAVLocation
        ldrb    wzr, [x0]
    ALTERNATE_ENTRY RhpCopyMultibyteWithWriteBarrierSrcAVLocation
        ldrb    wzr, [x1]

        ; tail-call to the GC-safe memcpy implementation
        b       memcpyGCRefsWithWriteBarrier

NothingToCopy_RhpCopyMultibyteWithWriteBarrier
        ; dest is already still in x0
        ret
    LEAF_END

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;
;; void* RhpCopyAnyWithWriteBarrier(void*, void*, size_t)
;;
;; The purpose of this wrapper is to hoist the potential null reference exceptions of copying memory up to a place where
;; the stack unwinder and exception dispatch can properly transform the exception into a managed exception and dispatch
;; it to managed code.
;; Runs a card table update via RhpBulkWriteBarrier after the copy if it contained GC pointers
;;

    LEAF_ENTRY    RhpCopyAnyWithWriteBarrier

        ; x0    dest
        ; x1    src
        ; x2    count

        ; check for a zero-length copy
        cbz     x2, NothingToCopy_RhpCopyAnyWithWriteBarrier

        ; Now check the dest and src pointers.  If they AV, the EH subsystem will recognize the address of the AV,
        ; unwind the frame, and fixup the stack to make it look like the (managed) caller AV'ed, which will be 
        ; translated to a managed exception as usual.
    ALTERNATE_ENTRY RhpCopyAnyWithWriteBarrierDestAVLocation
        ldrb    wzr, [x0]
    ALTERNATE_ENTRY RhpCopyAnyWithWriteBarrierSrcAVLocation
        ldrb    wzr, [x1]

        ; tail-call to the GC-safe memcpy implementation
        b       memcpyAnyWithWriteBarrier

NothingToCopy_RhpCopyAnyWithWriteBarrier
        ; dest is already still in x0
        ret

    LEAF_END

    end