2 // Copyright (c) Microsoft. All rights reserved.
3 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
7 #include "unixasmmacros.inc"
9 // Mark start of the code region that we patch at runtime
10 LEAF_ENTRY JIT_PatchedCodeStart, _TEXT
12 LEAF_END JIT_PatchedCodeStart, _TEXT
14 // This is used by the mechanism to hold either the JIT_WriteBarrier_PreGrow
15 // or JIT_WriteBarrier_PostGrow code (depending on the state of the GC). It _WILL_
16 // change at runtime as the GC changes. Initially it should simply be a copy of the
17 // larger of the two functions (JIT_WriteBarrier_PostGrow) to ensure we have created
18 // enough space to copy that code in.
20 LEAF_ENTRY JIT_WriteBarrier, _TEXT
23 // In debug builds, this just contains jump to the debug version of the write barrier by default
24 jmp JIT_WriteBarrier_Debug
27 // Do the move into the GC . It is correct to take an AV here, the EH code
28 // figures out that this came from a WriteBarrier and correctly maps it back
29 // to the managed method which called the WriteBarrier (see setup in
30 // InitializeExceptionHandling, vm\exceptionhandling.cpp).
33 NOP_3_BYTE // padding for alignment of constant
35 // Can't compare a 64 bit immediate, so we have to move them into a
36 // register. Values of these immediates will be patched at runtime.
37 // By using two registers we can pipeline better. Should we decide to use
38 // a special non-volatile calling convention, this should be changed to
41 movabs rax, 0F0F0F0F0F0F0F0F0h
43 // Check the lower and upper ephemeral region bounds
47 nop // padding for alignment of constant
49 movabs r8, 0F0F0F0F0F0F0F0F0h
54 nop // padding for alignment of constant
56 movabs rax, 0F0F0F0F0F0F0F0F0h
58 // Touch the card table entry, if not already dirty.
60 cmp byte ptr [rdi + rax], 0FFh
65 mov byte ptr [rdi + rax], 0FFh
71 // make sure this guy is bigger than any of the other guys
74 LEAF_END_MARKED JIT_WriteBarrier, _TEXT
76 // Mark start of the code region that we patch at runtime
77 LEAF_ENTRY JIT_PatchedCodeLast, _TEXT
79 LEAF_END JIT_PatchedCodeLast, _TEXT
81 // There is an even more optimized version of these helpers possible which takes
82 // advantage of knowledge of which way the ephemeral heap is growing to only do 1/2
83 // that check (this is more significant in the JIT_WriteBarrier case).
85 // Additionally we can look into providing helpers which will take the src/dest from
86 // specific registers (like x86) which _could_ (??) make for easier register allocation
87 // for the JIT64, however it might lead to having to have some nasty code that treats
88 // these guys really special like... :(.
90 // Version that does the move, checks whether or not it's in the GC and whether or not
91 // it needs to have it's card updated
93 // void JIT_CheckedWriteBarrier(Object** dst, Object* src)
94 LEAF_ENTRY JIT_CheckedWriteBarrier, _TEXT
96 // When WRITE_BARRIER_CHECK is defined _NotInHeap will write the reference
97 // but if it isn't then it will just return.
99 // See if this is in GCHeap
100 PREPARE_EXTERNAL_VAR g_lowest_address, rax
103 PREPARE_EXTERNAL_VAR g_highest_address, rax
110 // See comment above about possible AV
113 LEAF_END_MARKED JIT_CheckedWriteBarrier, _TEXT
115 // JIT_ByRefWriteBarrier has weird symantics, see usage in StubLinkerX86.cpp
118 // RDI - address of ref-field (assigned to)
119 // RSI - address of the data (source)
120 // RCX can be trashed
122 // RDI, RSI are incremented by SIZEOF(LPVOID)
123 LEAF_ENTRY JIT_ByRefWriteBarrier, _TEXT
127 // If !WRITE_BARRIER_CHECK do the write first, otherwise we might have to do some ShadowGC stuff
128 #ifndef WRITE_BARRIER_CHECK
133 // When WRITE_BARRIER_CHECK is defined _NotInHeap will write the reference
134 // but if it isn't then it will just return.
136 // See if this is in GCHeap
137 PREPARE_EXTERNAL_VAR g_lowest_address, rax
139 jb NotInHeap_ByRefWriteBarrier
140 PREPARE_EXTERNAL_VAR g_highest_address, rax
142 jnb NotInHeap_ByRefWriteBarrier
144 #ifdef WRITE_BARRIER_CHECK
145 // we can only trash rcx in this function so in _DEBUG we need to save
146 // some scratch registers.
150 // **ALSO update the shadow GC heap if that is enabled**
151 // Do not perform the work if g_GCShadow is 0
152 PREPARE_EXTERNAL_VAR g_GCShadow, rax
154 je NoShadow_ByRefWriteBarrier
156 // If we end up outside of the heap don't corrupt random memory
158 PREPARE_EXTERNAL_VAR g_lowest_address, rax
160 jb NoShadow_ByRefWriteBarrier
162 // Check that our adjusted destination is somewhere in the shadow gc
163 PREPARE_EXTERNAL_VAR g_GCShadow, rax
165 PREPARE_EXTERNAL_VAR g_GCShadowEnd, rax
167 ja NoShadow_ByRefWriteBarrier
169 // Write ref into real GC
171 // Write ref into shadow GC
174 // Ensure that the write to the shadow heap occurs before the read from
175 // the GC heap so that race conditions are caught by INVALIDGCVALUE
178 // Check that GC/ShadowGC values match
182 je DoneShadow_ByRefWriteBarrier
183 mov r11, INVALIDGCVALUE
186 jmp DoneShadow_ByRefWriteBarrier
188 // If we don't have a shadow GC we won't have done the write yet
189 NoShadow_ByRefWriteBarrier:
192 // If we had a shadow GC then we already wrote to the real GC at the same time
193 // as the shadow GC so we want to jump over the real write immediately above.
194 // Additionally we know for sure that we are inside the heap and therefore don't
195 // need to replicate the above checks.
196 DoneShadow_ByRefWriteBarrier:
201 // See if we can just quick out
202 PREPARE_EXTERNAL_VAR g_ephemeral_low, rax
204 jb Exit_ByRefWriteBarrier
205 PREPARE_EXTERNAL_VAR g_ephemeral_high, rax
207 jnb Exit_ByRefWriteBarrier
209 // move current rdi value into rcx and then increment the pointers
214 // Check if we need to update the card table
217 PREPARE_EXTERNAL_VAR g_card_table, rax
222 // Check if this card is dirty
223 cmp byte ptr [rcx], 0FFh
224 jne UpdateCardTable_ByRefWriteBarrier
227 UpdateCardTable_ByRefWriteBarrier:
228 mov byte ptr [rcx], 0FFh
232 NotInHeap_ByRefWriteBarrier:
233 // If WRITE_BARRIER_CHECK then we won't have already done the mov and should do it here
234 // If !WRITE_BARRIER_CHECK we want _NotInHeap and _Leave to be the same and have both
236 #ifdef WRITE_BARRIER_CHECK
240 Exit_ByRefWriteBarrier:
241 // Increment the pointers before leaving
246 LEAF_END JIT_ByRefWriteBarrier, _TEXT