Fix RhpLoopHijack to stop trashing important registers

The loop hijack worker routine is not honoring the contract that it should be.  Namely, the runtime is not allowed to trash any registers in our worker (except r12 on ARM).  The two big oversights were scratch FP registers and the flags registers.

I have also added a per-module map from loop index to target address (thus requiring all the shash.h includes).  This primarily helps gcstress throughput because the loop indirection cell address calculation ends up being surprisingly lengthy.  I considered the other obvious approach of "back-patching" the loop indirection cell in the gcstress case (normal loop hijacking does this, but under gcstress, we do not).  However, I ended up preferring this because it could help GC suspension latency in normal operation.

[tfs-changeset: 1573401]

1 files changed, 6 insertions, 0 deletions

diff --git a/src/Native/Runtime/module.h b/src/Native/Runtime/module.h
index 31cdfd029..5eebff5cd 100644
--- a/src/Native/Runtime/module.h
+++ b/src/Native/Runtime/module.h
@@ -146,6 +146,8 @@ public:
     bool IsFinalizerInitComplete() { return m_fFinalizerInitComplete; }
     void SetFinalizerInitComplete() { m_fFinalizerInitComplete = true; }
 
+    void * RecoverLoopHijackTarget(UInt32 entryIndex, ModuleHeader * pModuleHeader);
+
 private:
     Module(ModuleHeader * pModuleHeader);
 #ifdef FEATURE_CUSTOM_IMPORTS
@@ -153,6 +155,7 @@ private:
     PTR_UInt8 GetBaseAddress() { return (PTR_UInt8)(size_t)GetOsModuleHandle(); }
 #endif // FEATURE_CUSTOM_IMPORTS
 
+
     static void UnsynchronizedHijackLoop(void ** ppvIndirectionCell, UInt32 cellIndex, 
                                          void * pvRedirStubsStart, UInt8 * pbDirtyBitmap);
 
@@ -171,5 +174,8 @@ private:
     PTR_StaticGcDesc            m_pStaticsGCInfo;
     PTR_StaticGcDesc            m_pThreadStaticsGCInfo;
     PTR_UInt8                   m_pStaticsGCDataSection;
+
+    ReaderWriterLock            m_loopHijackMapLock;
+    MapSHash<UInt32, void*>     m_loopHijackIndexToTargetMap;
 };