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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.
; ==++==
;
;
; ==--==
; ***********************************************************************
; File: JitHelpers_FastWriteBarriers.asm, see jithelp.asm for history
;
; Notes: these are the fast write barriers which are copied in to the
; JIT_WriteBarrier buffer (found in JitHelpers_Fast.asm).
; This code should never be executed at runtime and should end
; up effectively being treated as data.
; ***********************************************************************
include AsmMacros.inc
include asmconstants.inc
; Two super fast helpers that together do the work of JIT_WriteBarrier. These
; use inlined ephemeral region bounds and an inlined pointer to the card table.
;
; Until the GC does some major reshuffling, the ephemeral region will always be
; at the top of the heap, so given that we know the reference is inside the
; heap, we don't have to check against the upper bound of the ephemeral region
; (PreGrow version). Once the GC moves the ephemeral region, this will no longer
; be valid, so we use the PostGrow version to check both the upper and lower
; bounds. The inlined bounds and card table pointers have to be patched
; whenever they change.
;
; At anyone time, the memory pointed to by JIT_WriteBarrier will contain one
; of these functions. See StompWriteBarrierResize and StompWriteBarrierEphemeral
; in VM\AMD64\JITInterfaceAMD64.cpp and InitJITHelpers1 in VM\JITInterfaceGen.cpp
; for more info.
;
; READ THIS!!!!!!
; it is imperative that the addresses of of the values that we overwrite
; (card table, ephemeral region ranges, etc) are naturally aligned since
; there are codepaths that will overwrite these values while the EE is running.
;
LEAF_ENTRY JIT_WriteBarrier_PreGrow32, _TEXT
align 4
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
NOP_2_BYTE ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PreGrow32_PatchLabel_Lower
cmp rdx, 0F0F0F0F0h
jb Exit
shr rcx, 0Bh
PATCH_LABEL JIT_WriteBarrier_PreGrow32_PatchLabel_CardTable_Check
cmp byte ptr [rcx + 0F0F0F0F0h], 0FFh
jne UpdateCardTable
REPRET
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PreGrow32_PatchLabel_CardTable_Update
UpdateCardTable:
mov byte ptr [rcx + 0F0F0F0F0h], 0FFh
ret
align 16
Exit:
REPRET
LEAF_END_MARKED JIT_WriteBarrier_PreGrow32, _TEXT
LEAF_ENTRY JIT_WriteBarrier_PreGrow64, _TEXT
align 8
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
NOP_3_BYTE ; padding for alignment of constant
; Can't compare a 64 bit immediate, so we have to move it into a
; register. Value of this immediate will be patched at runtime.
PATCH_LABEL JIT_WriteBarrier_PreGrow64_Patch_Label_Lower
mov rax, 0F0F0F0F0F0F0F0F0h
; Check the lower ephemeral region bound.
cmp rdx, rax
jb Exit
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PreGrow64_Patch_Label_CardTable
mov rax, 0F0F0F0F0F0F0F0F0h
; Touch the card table entry, if not already dirty.
shr rcx, 0Bh
cmp byte ptr [rcx + rax], 0FFh
jne UpdateCardTable
REPRET
UpdateCardTable:
mov byte ptr [rcx + rax], 0FFh
ret
align 16
Exit:
REPRET
LEAF_END_MARKED JIT_WriteBarrier_PreGrow64, _TEXT
; See comments for JIT_WriteBarrier_PreGrow (above).
LEAF_ENTRY JIT_WriteBarrier_PostGrow64, _TEXT
align 8
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
NOP_3_BYTE ; padding for alignment of constant
; Can't compare a 64 bit immediate, so we have to move them into a
; register. Values of these immediates will be patched at runtime.
; By using two registers we can pipeline better. Should we decide to use
; a special non-volatile calling convention, this should be changed to
; just one.
PATCH_LABEL JIT_WriteBarrier_PostGrow64_Patch_Label_Lower
mov rax, 0F0F0F0F0F0F0F0F0h
; Check the lower and upper ephemeral region bounds
cmp rdx, rax
jb Exit
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PostGrow64_Patch_Label_Upper
mov r8, 0F0F0F0F0F0F0F0F0h
cmp rdx, r8
jae Exit
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PostGrow64_Patch_Label_CardTable
mov rax, 0F0F0F0F0F0F0F0F0h
; Touch the card table entry, if not already dirty.
shr rcx, 0Bh
cmp byte ptr [rcx + rax], 0FFh
jne UpdateCardTable
REPRET
UpdateCardTable:
mov byte ptr [rcx + rax], 0FFh
ret
align 16
Exit:
REPRET
LEAF_END_MARKED JIT_WriteBarrier_PostGrow64, _TEXT
LEAF_ENTRY JIT_WriteBarrier_PostGrow32, _TEXT
align 4
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
NOP_2_BYTE ; padding for alignment of constant
; Check the lower and upper ephemeral region bounds
PATCH_LABEL JIT_WriteBarrier_PostGrow32_PatchLabel_Lower
cmp rdx, 0F0F0F0F0h
jb Exit
NOP_3_BYTE ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PostGrow32_PatchLabel_Upper
cmp rdx, 0F0F0F0F0h
jae Exit
; Touch the card table entry, if not already dirty.
shr rcx, 0Bh
PATCH_LABEL JIT_WriteBarrier_PostGrow32_PatchLabel_CheckCardTable
cmp byte ptr [rcx + 0F0F0F0F0h], 0FFh
jne UpdateCardTable
REPRET
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_PostGrow32_PatchLabel_UpdateCardTable
UpdateCardTable:
mov byte ptr [rcx + 0F0F0F0F0h], 0FFh
ret
align 16
Exit:
REPRET
LEAF_END_MARKED JIT_WriteBarrier_PostGrow32, _TEXT
LEAF_ENTRY JIT_WriteBarrier_SVR32, _TEXT
align 4
;
; SVR GC has multiple heaps, so it cannot provide one single
; ephemeral region to bounds check against, so we just skip the
; bounds checking all together and do our card table update
; unconditionally.
;
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
shr rcx, 0Bh
NOP_3_BYTE ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_SVR32_PatchLabel_CheckCardTable
cmp byte ptr [rcx + 0F0F0F0F0h], 0FFh
jne UpdateCardTable
REPRET
nop ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_SVR32_PatchLabel_UpdateCardTable
UpdateCardTable:
mov byte ptr [rcx + 0F0F0F0F0h], 0FFh
ret
LEAF_END_MARKED JIT_WriteBarrier_SVR32, _TEXT
LEAF_ENTRY JIT_WriteBarrier_SVR64, _TEXT
align 8
;
; SVR GC has multiple heaps, so it cannot provide one single
; ephemeral region to bounds check against, so we just skip the
; bounds checking all together and do our card table update
; unconditionally.
;
; Do the move into the GC . It is correct to take an AV here, the EH code
; figures out that this came from a WriteBarrier and correctly maps it back
; to the managed method which called the WriteBarrier (see setup in
; InitializeExceptionHandling, vm\exceptionhandling.cpp).
mov [rcx], rdx
NOP_3_BYTE ; padding for alignment of constant
PATCH_LABEL JIT_WriteBarrier_SVR64_PatchLabel_CardTable
mov rax, 0F0F0F0F0F0F0F0F0h
shr rcx, 0Bh
cmp byte ptr [rcx + rax], 0FFh
jne UpdateCardTable
REPRET
UpdateCardTable:
mov byte ptr [rcx + rax], 0FFh
ret
LEAF_END_MARKED JIT_WriteBarrier_SVR64, _TEXT
end
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