Unify macOS ARM64 write protection holders with W^X ones (#54067)

* Unify macOS ARM64 write protection holders with W^X ones

This change removes the original holders that were added for changing
memory protection for executable code and moves the actual switching to
the recently added W^X holders.

The unixexports files don't support target specific symbols. So I needed
to export a dummy version of the PAL_JitWriteProtect for macOS x64.

2 files changed, 25 insertions, 36 deletions

diff --git a/src/coreclr/pal/inc/pal.h b/src/coreclr/pal/inc/pal.h
index d22c9ba8c8d..69d90522a0d 100644
--- a/src/coreclr/pal/inc/pal.h
+++ b/src/coreclr/pal/inc/pal.h
@@ -2760,32 +2760,14 @@ VirtualFree(
         IN SIZE_T dwSize,
         IN DWORD dwFreeType);
 
-#if defined(HOST_OSX) && defined(HOST_ARM64)
-#ifdef __cplusplus
-extern "C++" {
-struct PAL_JITWriteEnableHolder
-{
-public:
-  PAL_JITWriteEnableHolder(bool jitWriteEnable)
-  {
-      m_jitWriteEnableRestore = JITWriteEnable(jitWriteEnable);
-  };
-  ~PAL_JITWriteEnableHolder()
-  {
-      JITWriteEnable(m_jitWriteEnableRestore);
-  }
+#if defined(HOST_OSX)
 
-private:
-  bool JITWriteEnable(bool enable);
-  bool m_jitWriteEnableRestore;
-};
+PALIMPORT
+VOID
+PALAPI
+PAL_JitWriteProtect(bool writeEnable);
 
-inline
-PAL_JITWriteEnableHolder
-PAL_JITWriteEnable(IN bool enable) { return PAL_JITWriteEnableHolder(enable); }
-}
-#endif // __cplusplus
-#endif // defined(HOST_OSX) && defined(HOST_ARM64)
+#endif // defined(HOST_OSX)
 
 PALIMPORT
 BOOL
diff --git a/src/coreclr/pal/src/map/virtual.cpp b/src/coreclr/pal/src/map/virtual.cpp
index cea55e86e25..9267f4fdf1c 100644
--- a/src/coreclr/pal/src/map/virtual.cpp
+++ b/src/coreclr/pal/src/map/virtual.cpp
@@ -1760,22 +1760,29 @@ ExitVirtualProtect:
     return bRetVal;
 }
 
-#if defined(HOST_OSX) && defined(HOST_ARM64)
-bool
-PAL_JITWriteEnableHolder::JITWriteEnable(bool writeEnable)
+#if defined(HOST_OSX)
+PALAPI VOID PAL_JitWriteProtect(bool writeEnable)
 {
-    // Use a thread local to track per thread JIT Write enable state
-    // Per Apple, new threads start with MAP_JIT pages readable and executable (R-X) by default.
-    thread_local bool enabled = false;
-    bool result = enabled;
-    if (enabled != writeEnable)
+#if defined(HOST_ARM64)
+    thread_local int enabledCount = 0;
+    if (writeEnable)
     {
-        pthread_jit_write_protect_np(writeEnable ? 0 : 1);
-        enabled = writeEnable;
+        if (enabledCount++ == 0)
+        {
+            pthread_jit_write_protect_np(0);
+        }
+    }
+    else
+    {
+        if (--enabledCount == 0)
+        {
+            pthread_jit_write_protect_np(1);
+        }
+        _ASSERTE(enabledCount >= 0);
     }
-    return result;
+#endif // HOST_ARM64
 }
-#endif
+#endif // HOST_OSX
 
 #if HAVE_VM_ALLOCATE
 //---------------------------------------------------------------------------------------