Preallocate jump stubs for dynamic methods (#9883)

Preallocate jump stubs for dynamic methods

- This eliminates the possibility of running into an out-of-memory situation after compiling the method
- The temporary entry points block containing FixupPrecodes is extended for dynamic methods to include sufficient space for jump stubs
- When the target is too far for the FixupPrecode to encode a short relative jump, it instead does a short relative call or jump to the corresponding jump stub, which does an absolute jump to the target

2 files changed, 33 insertions, 0 deletions

diff --git a/src/vm/amd64/cgenamd64.cpp b/src/vm/amd64/cgenamd64.cpp
index 51aac1ebc6..497abcd502 100644
--- a/src/vm/amd64/cgenamd64.cpp
+++ b/src/vm/amd64/cgenamd64.cpp
@@ -727,6 +727,35 @@ INT32 rel32UsingJumpStub(INT32 UNALIGNED * pRel32, PCODE target, MethodDesc *pMe
     return static_cast<INT32>(offset);
 }
 
+INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr)
+{
+    CONTRACTL
+    {
+        THROWS; // emitBackToBackJump may throw (see emitJump)
+        GC_NOTRIGGER;
+    }
+    CONTRACTL_END;
+
+    TADDR baseAddr = (TADDR)pRel32 + 4;
+    _ASSERTE(FitsInI4(jumpStubAddr - baseAddr));
+
+    INT_PTR offset = target - baseAddr;
+    if (!FitsInI4(offset) INDEBUG(|| PEDecoder::GetForceRelocs()))
+    {
+        offset = jumpStubAddr - baseAddr;
+        if (!FitsInI4(offset))
+        {
+            _ASSERTE(!"jump stub was not in expected range");
+            EEPOLICY_HANDLE_FATAL_ERROR(COR_E_EXECUTIONENGINE);
+        }
+
+        emitBackToBackJump((LPBYTE)jumpStubAddr, (LPVOID)target);
+    }
+
+    _ASSERTE(FitsInI4(offset));
+    return static_cast<INT32>(offset);
+}
+
 BOOL DoesSlotCallPrestub(PCODE pCode)
 {
     CONTRACTL {
diff --git a/src/vm/amd64/cgencpu.h b/src/vm/amd64/cgencpu.h
index 769f4029ee..2d4dce0e6e 100644
--- a/src/vm/amd64/cgencpu.h
+++ b/src/vm/amd64/cgencpu.h
@@ -57,6 +57,7 @@ EXTERN_C void FastCallFinalizeWorker(Object *obj, PCODE funcPtr);
 //#define HAS_REMOTING_PRECODE                  1    // TODO: Implement
 #define HAS_FIXUP_PRECODE                       1
 #define HAS_FIXUP_PRECODE_CHUNKS                1
+#define FIXUP_PRECODE_PREALLOCATE_DYNAMIC_METHOD_JUMP_STUBS 1
 
 // ThisPtrRetBufPrecode one is necessary for closed delegates over static methods with return buffer
 #define HAS_THISPTR_RETBUF_PRECODE              1
@@ -381,6 +382,9 @@ void EncodeLoadAndJumpThunk (LPBYTE pBuffer, LPVOID pv, LPVOID pTarget);
 // Get Rel32 destination, emit jumpStub if necessary
 INT32 rel32UsingJumpStub(INT32 UNALIGNED * pRel32, PCODE target, MethodDesc *pMethod, LoaderAllocator *pLoaderAllocator = NULL);
 
+// Get Rel32 destination, emit jumpStub if necessary into a preallocated location
+INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr);
+
 void emitCOMStubCall (ComCallMethodDesc *pCOMMethod, PCODE target);
 
 void emitJump(LPBYTE pBuffer, LPVOID target);