Expose a hosting interface for the JIT.

This is the first significant step towards removing the JIT's dependence on utilcode.
This change introduces a new interface, `ICorJitHost`, that allows functionality that
would usually be provided by the OS to be overridden by the program that is hosting
the JIT. At the moment, this is limited to memory allocation and configuration value
(e.g. environment variable) access. If the JIT exports a function named `jitStartup`,
an instance of the `ICorJitHost` must be provided via that function before the first
call to `getJit`.

The VM and other implementors of the JIT interface have been updated accordingly.
Most implementors should use the common implementation of `ICorJitHost` (cleverly
named `JitHost`) in utilcode which respects the CLR's hosting policy.

Note that this change does not update RyuJIT (or any other JITs) to use any of the
functionality exposed by `ICorJitHost`; that work is left for future changes.

[tfs-changeset: 1578176]

5 files changed, 19 insertions, 8 deletions

diff --git a/src/jit/ClrJit.exports b/src/jit/ClrJit.exports
index 9a914d7038..0126e63b4d 100644
--- a/src/jit/ClrJit.exports
+++ b/src/jit/ClrJit.exports
@@ -1,2 +1,3 @@
 getJit
+jitStartup
 sxsJitStartup
diff --git a/src/jit/dll/clrjit.def b/src/jit/dll/clrjit.def
index 73a6ba1ae1..1603af74ca 100644
--- a/src/jit/dll/clrjit.def
+++ b/src/jit/dll/clrjit.def
@@ -3,4 +3,5 @@
 ; See the LICENSE file in the project root for more information.
 EXPORTS
     getJit
-    sxsJitStartup
\ No newline at end of file
+    jitStartup
+    sxsJitStartup
diff --git a/src/jit/ee_il_dll.cpp b/src/jit/ee_il_dll.cpp
index f32f87557f..f0da62d153 100644
--- a/src/jit/ee_il_dll.cpp
+++ b/src/jit/ee_il_dll.cpp
@@ -19,8 +19,10 @@ XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
 #endif
 #include "emit.h"
 
+
 /*****************************************************************************/
 
+static ICorJitHost* g_jitHost = nullptr;
 static CILJit* ILJitter = 0;        // The one and only JITTER I return
 #ifndef FEATURE_MERGE_JIT_AND_ENGINE
 HINSTANCE g_hInst = NULL;
@@ -45,8 +47,11 @@ JitOptions jitOpts =
 
 /*****************************************************************************/
 
-void jitStartup()
+extern "C"
+void __stdcall jitStartup(ICorJitHost* jitHost)
 {
+    g_jitHost = jitHost;
+
 #ifdef FEATURE_TRACELOGGING
     JitTelemetry::NotifyDllProcessAttach();
 #endif
@@ -61,13 +66,16 @@ void jitShutdown()
 #endif
 }
 
+
 /*****************************************************************************
  *  jitOnDllProcessAttach() called by DllMain() when jit.dll is loaded
  */
 
 void jitOnDllProcessAttach()
 {
-    jitStartup();
+#if COR_JIT_EE_VERSION <= 460
+    jitStartup(JitHost::getJitHost());
+#endif
 }
 
 /*****************************************************************************
@@ -79,7 +87,6 @@ void jitOnDllProcessDetach()
     jitShutdown();
 }
 
-
 #ifndef FEATURE_MERGE_JIT_AND_ENGINE
 
 extern "C"
@@ -139,9 +146,6 @@ ICorJitCompiler* __stdcall getJit()
     if (ILJitter == 0)
     {
         ILJitter = new (CILJitSingleton) CILJit();
-#ifdef FEATURE_MERGE_JIT_AND_ENGINE
-        jitStartup();
-#endif
     }
     return(ILJitter);
 }
diff --git a/src/jit/jitpch.h b/src/jit/jitpch.h
index 7c333a72c2..a3c7e24464 100644
--- a/src/jit/jitpch.h
+++ b/src/jit/jitpch.h
@@ -16,6 +16,10 @@
 #include <cstdlib>
 #include <intrin.h>
 
+#if COR_JIT_EE_VERSION <= 460
+#include "corjithost.h"
+#include "jithost.h"
+#endif
 #include "jit.h"
 #include "iallocator.h"
 #include "hashbv.h"
diff --git a/src/jit/protojit/protojit.def b/src/jit/protojit/protojit.def
index 73a6ba1ae1..1603af74ca 100644
--- a/src/jit/protojit/protojit.def
+++ b/src/jit/protojit/protojit.def
@@ -3,4 +3,5 @@
 ; See the LICENSE file in the project root for more information.
 EXPORTS
     getJit
-    sxsJitStartup
\ No newline at end of file
+    jitStartup
+    sxsJitStartup