Fix to not reuse preallocated jump stubs for dynamic methods (#16941)

Fix to not reuse preallocated jump stubs for dynamic methods

Fixes https://github.com/dotnet/coreclr/issues/16940
- Allocate an extra jump stub per temporary entry points chunk that is shared by all precodes in the chunk. This jump stub always points to PrecodeFixupThunk.
- Use that for PrecodeFixupThunk, and use the precode-associated jump stub for pointing to the jitted code
- Considered allocating the extra jump stub only if coreclr is far away, but it involves reallocation which may be common in some environments/scenarios. Figured 12 extra bytes per dynamic type is not too significant.

2 files changed, 10 insertions, 3 deletions

diff --git a/src/vm/amd64/cgenamd64.cpp b/src/vm/amd64/cgenamd64.cpp
index 56e3bfa738..6d11c7f0fa 100644
--- a/src/vm/amd64/cgenamd64.cpp
+++ b/src/vm/amd64/cgenamd64.cpp
@@ -689,7 +689,7 @@ INT32 rel32UsingJumpStub(INT32 UNALIGNED * pRel32, PCODE target, MethodDesc *pMe
     return static_cast<INT32>(offset);
 }
 
-INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr)
+INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr, bool emitJump)
 {
     CONTRACTL
     {
@@ -711,7 +711,14 @@ INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCO
             EEPOLICY_HANDLE_FATAL_ERROR(COR_E_EXECUTIONENGINE);
         }
 
-        emitBackToBackJump((LPBYTE)jumpStubAddr, (LPVOID)target);
+        if (emitJump)
+        {
+            emitBackToBackJump((LPBYTE)jumpStubAddr, (LPVOID)target);
+        }
+        else
+        {
+            _ASSERTE(decodeBackToBackJump(jumpStubAddr) == target);
+        }
     }
 
     _ASSERTE(FitsInI4(offset));
diff --git a/src/vm/amd64/cgencpu.h b/src/vm/amd64/cgencpu.h
index 9136b168aa..ab049a49e2 100644
--- a/src/vm/amd64/cgencpu.h
+++ b/src/vm/amd64/cgencpu.h
@@ -383,7 +383,7 @@ INT32 rel32UsingJumpStub(INT32 UNALIGNED * pRel32, PCODE target, MethodDesc *pMe
     LoaderAllocator *pLoaderAllocator = NULL, bool throwOnOutOfMemoryWithinRange = true);
 
 // Get Rel32 destination, emit jumpStub if necessary into a preallocated location
-INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr);
+INT32 rel32UsingPreallocatedJumpStub(INT32 UNALIGNED * pRel32, PCODE target, PCODE jumpStubAddr, bool emitJump);
 
 void emitCOMStubCall (ComCallMethodDesc *pCOMMethod, PCODE target);