Fix BackoutJitData (#54711)

* Fix BackoutJitData

The RemoveJitData that the BackoutJitData calls requires the code
header to be copied to the final location. This change fixes it.

I've also found that in one of my previous changes, I've accidentally
enabled jitting into a scratch buffer by default by adding the
FEATURE_WXORX define unconditionally. So I am removing it in this change
for non Apple Silicon, it will be replaced by a dynamic check whether W^X 
is enabled in the final W^X change.

Author: janvorli

src/coreclr/vm/codeman.cpp

@@ -2685,7 +2685,11 @@ void EEJitManager::allocCode(MethodDesc* pMD, size_t blockSize, size_t reserveFo
         pCodeHdr = ((CodeHeader *)pCode) - 1;
 
         *pAllocatedSize = sizeof(CodeHeader) + totalSize;
-#define FEATURE_WXORX        
+
+#if defined(HOST_OSX) && defined(HOST_ARM64)
+#define FEATURE_WXORX
+#endif
+
 #ifdef FEATURE_WXORX
         pCodeHdrRW = (CodeHeader *)new BYTE[*pAllocatedSize];
 #else

src/coreclr/vm/jitinterface.cpp

@@ -11211,6 +11211,27 @@ void CEEJitInfo::GetProfilingHandle(bool                      *pbHookFunction,
     *pbIndirectedHandles = false;
 }
 
+/*********************************************************************/
+void CEEJitInfo::WriteCodeBytes()
+{
+    LIMITED_METHOD_CONTRACT;
+
+#ifdef USE_INDIRECT_CODEHEADER
+    if (m_pRealCodeHeader != NULL)
+    {
+        // Restore the read only version of the real code header
+        m_CodeHeaderRW->SetRealCodeHeader(m_pRealCodeHeader);
+        m_pRealCodeHeader = NULL;
+    }
+#endif // USE_INDIRECT_CODEHEADER
+
+    if (m_CodeHeaderRW != m_CodeHeader)
+    {
+        ExecutableWriterHolder<void> codeWriterHolder((void *)m_CodeHeader, m_codeWriteBufferSize);
+        memcpy(codeWriterHolder.GetRW(), m_CodeHeaderRW, m_codeWriteBufferSize);
+    }
+}
+
 /*********************************************************************/
 void CEEJitInfo::BackoutJitData(EEJitManager * jitMgr)
 {
@@ -11219,6 +11240,10 @@ void CEEJitInfo::BackoutJitData(EEJitManager * jitMgr)
         GC_TRIGGERS;
     } CONTRACTL_END;
 
+    // The RemoveJitData call below requires the m_CodeHeader to be valid, so we need to write
+    // the code bytes to the target memory location.
+    WriteCodeBytes();
+
     CodeHeader* pCodeHeader = m_CodeHeader;
     if (pCodeHeader)
         jitMgr->RemoveJitData(pCodeHeader, m_GCinfo_len, m_EHinfo_len);
@@ -11232,20 +11257,7 @@ void CEEJitInfo::WriteCode(EEJitManager * jitMgr)
         GC_TRIGGERS;
     } CONTRACTL_END;
 
-#ifdef USE_INDIRECT_CODEHEADER
-    if (m_pRealCodeHeader != NULL)
-    {
-        // Restore the read only version of the real code header
-        m_CodeHeaderRW->SetRealCodeHeader(m_pRealCodeHeader);
-        m_pRealCodeHeader = NULL;
-    }
-#endif // USE_INDIRECT_CODEHEADER
-
-    if (m_CodeHeaderRW != m_CodeHeader)
-    {
-        ExecutableWriterHolder<void> codeWriterHolder((void *)m_CodeHeader, m_codeWriteBufferSize);
-        memcpy(codeWriterHolder.GetRW(), m_CodeHeaderRW, m_codeWriteBufferSize);
-    }
+    WriteCodeBytes();
 
     // Now that the code header was written to the final location, publish the code via the nibble map
     jitMgr->NibbleMapSet(m_pCodeHeap, m_CodeHeader->GetCodeStartAddress(), TRUE);

src/coreclr/vm/jitinterface.h

@@ -941,6 +941,8 @@ class CEEJitInfo : public CEEInfo
 
 protected :
 
+    void WriteCodeBytes();
+
 #ifdef FEATURE_PGO
     // PGO data
     struct ComputedPgoData