[Local GC] Scaffolding for loading a standalone GC (#11242)

* Configure the build system to build a CoreCLR capable of loading a standalone GC

* Proto-implementation of dynamic GC loading

* Build the GC with the VM's CMakeLists when doing a non-standalone build of the GC

* [Local GC] Introduce a new feature define, FEATURE_STANDALONE_GC_ONLY, to be used by the CI to explicitly test local GC dynamic loading code paths

* Fix the FEATURE_STANDALONE_GC_ONLY build for unix linkers

* Rebase against master

* Code review feedback: use the existing Unix exports file

11 files changed, 75 insertions, 54 deletions

diff --git a/src/gc/CMakeLists.txt b/src/gc/CMakeLists.txt
index 59c18ffd87..f55c1a9a6f 100644
--- a/src/gc/CMakeLists.txt
+++ b/src/gc/CMakeLists.txt
@@ -1,24 +1,16 @@
 set(CMAKE_INCLUDE_CURRENT_DIR ON)
 
-include_directories(BEFORE ${CMAKE_CURRENT_SOURCE_DIR}) 
+include_directories(BEFORE ${CMAKE_CURRENT_SOURCE_DIR})
 include_directories(BEFORE ${CLR_DIR}/src/vm)
 include_directories(BEFORE ${CLR_DIR}/src/vm/${ARCH_SOURCES_DIR})
 
+add_definitions(-DBUILD_AS_STANDALONE)
+
 if(CLR_CMAKE_PLATFORM_UNIX)
   add_compile_options(-fPIC)
 endif(CLR_CMAKE_PLATFORM_UNIX)
 
-if(CMAKE_CONFIGURATION_TYPES)
-  foreach (Config DEBUG CHECKED)  
-     set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS $<$<CONFIG:${Config}>:WRITE_BARRIER_CHECK=1>)
-  endforeach (Config)
-else()
-  if(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL DEBUG OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL CHECKED)
-    add_definitions(-DWRITE_BARRIER_CHECK=1)
-  endif(UPPERCASE_CMAKE_BUILD_TYPE STREQUAL DEBUG OR UPPERCASE_CMAKE_BUILD_TYPE STREQUAL CHECKED)
-endif(CMAKE_CONFIGURATION_TYPES)
-
-set( GC_SOURCES_DAC_AND_WKS_COMMON
+set( GC_SOURCES
   gccommon.cpp
   gcscan.cpp
   gcsvr.cpp
@@ -27,28 +19,18 @@ set( GC_SOURCES_DAC_AND_WKS_COMMON
   handletablecore.cpp
   handletablescan.cpp
   objecthandle.cpp
-  softwarewritewatch.cpp)
-
-set( GC_SOURCES_WKS
-  ${GC_SOURCES_DAC_AND_WKS_COMMON}
+  softwarewritewatch.cpp
   gchandletable.cpp
   gceesvr.cpp
   gceewks.cpp
   handletablecache.cpp)
 
-set( GC_SOURCES_DAC
-  ${GC_SOURCES_DAC_AND_WKS_COMMON})
-
-if(FEATURE_STANDALONE_GC)
-  if(NOT CLR_CMAKE_PLATFORM_UNIX)
-    set ( GC_SOURCES_WKS
-      ${GC_SOURCES_WKS}
-      windows/gcenv.windows.cpp)
-  endif(NOT CLR_CMAKE_PLATFORM_UNIX)
-endif(FEATURE_STANDALONE_GC)
+if(NOT CLR_CMAKE_PLATFORM_UNIX)
+set ( GC_SOURCES
+  ${GC_SOURCES}
+  windows/gcenv.windows.cpp)
+endif(NOT CLR_CMAKE_PLATFORM_UNIX)
 
-convert_to_absolute_path(GC_SOURCES_WKS ${GC_SOURCES_WKS})
-convert_to_absolute_path(GC_SOURCES_DAC ${GC_SOURCES_DAC})
+convert_to_absolute_path(GC_SOURCES ${GC_SOURCES})
 
-add_subdirectory(wks)
-add_subdirectory(dac)
+add_library_clr(gc_standalone STATIC ${GC_SOURCES})
diff --git a/src/gc/dac/CMakeLists.txt b/src/gc/dac/CMakeLists.txt
deleted file mode 100644
index 1f1c9ebe5c..0000000000
--- a/src/gc/dac/CMakeLists.txt
+++ /dev/null
@@ -1,2 +0,0 @@
-include(${CLR_DIR}/dac.cmake)
-add_library_clr(gc_dac STATIC ${GC_SOURCES_DAC})
diff --git a/src/gc/gc.h b/src/gc/gc.h
index 07ae6c916c..2da0cb3966 100644
--- a/src/gc/gc.h
+++ b/src/gc/gc.h
@@ -27,16 +27,17 @@ Module Name:
 
 #include "gcinterface.h"
 #include "env/gcenv.os.h"
-#include "env/gcenv.ee.h"
 
-#ifdef FEATURE_STANDALONE_GC
+#ifdef BUILD_AS_STANDALONE
 #include "gcenv.ee.standalone.inl"
 
 // GCStress does not currently work with Standalone GC
 #ifdef STRESS_HEAP
  #undef STRESS_HEAP
 #endif // STRESS_HEAP
-#endif // FEATURE_STANDALONE_GC
+#else
+#include "env/gcenv.ee.h"
+#endif // BUILD_AS_STANDALONE
 
 /*
  * Promotion Function Prototypes
diff --git a/src/gc/gccommon.cpp b/src/gc/gccommon.cpp
index 4950809cda..d7c572260a 100644
--- a/src/gc/gccommon.cpp
+++ b/src/gc/gccommon.cpp
@@ -17,9 +17,9 @@
 IGCHeapInternal* g_theGCHeap;
 IGCHandleManager* g_theGCHandleManager;
 
-#ifdef FEATURE_STANDALONE_GC
+#ifdef BUILD_AS_STANDALONE
 IGCToCLR* g_theGCToCLR;
-#endif // FEATURE_STANDALONE_GC
+#endif // BUILD_AS_STANDALONE
 
 #ifdef GC_CONFIG_DRIVEN
 size_t gc_global_mechanisms[MAX_GLOBAL_GC_MECHANISMS_COUNT];
@@ -143,7 +143,30 @@ namespace SVR
     extern void PopulateDacVars(GcDacVars* dacVars);
 }
 
-bool InitializeGarbageCollector(IGCToCLR* clrToGC, IGCHeap** gcHeap, IGCHandleManager** gcHandleManager, GcDacVars* gcDacVars)
+//------------------------------------------------------------------
+// Externally-facing GC symbols, used to initialize the GC
+// -----------------------------------------------------------------
+
+#ifdef _MSC_VER
+#define DLLEXPORT __declspec(dllexport)
+#else
+#define DLLEXPORT __attribute__ ((visibility ("default")))
+#endif // _MSC_VER
+
+#ifdef BUILD_AS_STANDALONE
+#define GC_API extern "C" DLLEXPORT
+#else
+#define GC_API extern "C"
+#endif // BUILD_AS_STANDALONE
+
+GC_API
+bool
+InitializeGarbageCollector(
+    /* In */  IGCToCLR* clrToGC,
+    /* Out */ IGCHeap** gcHeap,
+    /* Out */ IGCHandleManager** gcHandleManager,
+    /* Out */ GcDacVars* gcDacVars
+    )
 {
     LIMITED_METHOD_CONTRACT;
 
@@ -184,7 +207,7 @@ bool InitializeGarbageCollector(IGCToCLR* clrToGC, IGCHeap** gcHeap, IGCHandleMa
 
     g_theGCHeap = heap;
 
-#ifdef FEATURE_STANDALONE_GC
+#ifdef BUILD_AS_STANDALONE
     assert(clrToGC != nullptr);
     g_theGCToCLR = clrToGC;
 #else
diff --git a/src/gc/gcenv.ee.standalone.inl b/src/gc/gcenv.ee.standalone.inl
index f6954fc476..31c3455d7b 100644
--- a/src/gc/gcenv.ee.standalone.inl
+++ b/src/gc/gcenv.ee.standalone.inl
@@ -5,12 +5,17 @@
 #ifndef __GCTOENV_EE_STANDALONE_INL__
 #define __GCTOENV_EE_STANDALONE_INL__
 
-#include "env/gcenv.ee.h"
+#include "gcinterface.h"
 
 // The singular interface instance. All calls in GCToEEInterface
 // will be fowarded to this interface instance.
 extern IGCToCLR* g_theGCToCLR;
 
+namespace
+{
+
+#include "env/gcenv.ee.h"
+
 // A note about this:
 // In general, we don't want to pretend to be smarter than the compiler
 // and force it to inline things. However, inlining is here is required
@@ -238,4 +243,6 @@ ALWAYS_INLINE MethodTable* GCToEEInterface::GetFreeObjectMethodTable()
 }
 #undef ALWAYS_INLINE
 
+} // anonymous namespace
+
 #endif // __GCTOENV_EE_STANDALONE_INL__
diff --git a/src/gc/gcinterface.ee.h b/src/gc/gcinterface.ee.h
index 7b868e780e..8290572cd4 100644
--- a/src/gc/gcinterface.ee.h
+++ b/src/gc/gcinterface.ee.h
@@ -9,9 +9,9 @@
 // of the execution engine. Everything that the GC does that requires the EE
 // to be informed or that requires EE action must go through this interface.
 //
-// When FEATURE_STANDALONE_GC is defined, this class is named IGCToCLR and is
+// When BUILD_AS_STANDALONE is defined, this class is named IGCToCLR and is
 // an abstract class. The EE will provide a class that fulfills this interface,
-// and the GC will dispatch virtually on it to call into the EE. When FEATURE_STANDALONE_GC
+// and the GC will dispatch virtually on it to call into the EE. When BUILD_AS_STANDALONE
 // is not defined, this class is named GCToEEInterface and the GC will dispatch statically on it.
 class IGCToCLR {
 public:
diff --git a/src/gc/gcinterface.h b/src/gc/gcinterface.h
index 552a8caec8..425745b0cb 100644
--- a/src/gc/gcinterface.h
+++ b/src/gc/gcinterface.h
@@ -171,15 +171,24 @@ class Object;
 class IGCHeap;
 class IGCHandleManager;
 
-// Initializes the garbage collector. Should only be called
-// once, during EE startup. Returns true if the initialization
-// was successful, false otherwise.
-bool InitializeGarbageCollector(IGCToCLR* clrToGC, IGCHeap** gcHeap, IGCHandleManager** gcHandleTable, GcDacVars* gcDacVars);
+// The function that initialzes the garbage collector.
+// Should only be called once: here, during EE startup.
+// Returns true if the initialization was successful, false otherwise.
+typedef bool (*InitializeGarbageCollectorFunction)(
+    /* In  */ IGCToCLR*,
+    /* Out */ IGCHeap**,
+    /* Out */ IGCHandleManager**,
+    /* Out */ GcDacVars*
+);
+
+// The name of the function that initializes the garbage collector,
+// to be used as an argument to GetProcAddress.
+#define INITIALIZE_GC_FUNCTION_NAME "InitializeGarbageCollector"
 
 // The runtime needs to know whether we're using workstation or server GC 
 // long before the GCHeap is created. This function sets the type of
 // heap that will be created, before InitializeGarbageCollector is called
-// and the heap is actually recated.
+// and the heap is actually created.
 void InitializeHeapType(bool bServerHeap);
 
 #ifdef WRITE_BARRIER_CHECK
diff --git a/src/gc/sample/GCSample.cpp b/src/gc/sample/GCSample.cpp
index 0a771b7e91..43cb23878e 100644
--- a/src/gc/sample/GCSample.cpp
+++ b/src/gc/sample/GCSample.cpp
@@ -107,6 +107,8 @@ void WriteBarrier(Object ** dst, Object * ref)
     ErectWriteBarrier(dst, ref);
 }
 
+extern "C" bool InitializeGarbageCollector(IGCToCLR* clrToGC, IGCHeap** gcHeap, IGCHandleManager** gcHandleManager, GcDacVars* gcDacVars);
+
 int __cdecl main(int argc, char* argv[])
 {
     //
diff --git a/src/gc/sample/gcenv.h b/src/gc/sample/gcenv.h
index 4505f1af30..14f60d8c6e 100644
--- a/src/gc/sample/gcenv.h
+++ b/src/gc/sample/gcenv.h
@@ -4,9 +4,9 @@
 
 // The sample is to be kept simple, so building the sample
 // in tandem with a standalone GC is currently not supported.
-#ifdef FEATURE_STANDALONE_GC
-#undef FEATURE_STANDALONE_GC
-#endif // FEATURE_STANDALONE_GC
+#ifdef BUILD_AS_STANDALONE
+#undef BUILD_AS_STANDALONE
+#endif // BUILD_AS_STANDALONE
 
 #if defined(_DEBUG)
 #ifndef _DEBUG_IMPL
diff --git a/src/gc/unix/gcenv.unix.cpp b/src/gc/unix/gcenv.unix.cpp
index bca0dfedf2..cebc515345 100644
--- a/src/gc/unix/gcenv.unix.cpp
+++ b/src/gc/unix/gcenv.unix.cpp
@@ -32,9 +32,9 @@ static_assert(sizeof(uint64_t) == 8, "unsigned long isn't 8 bytes");
 #include "gcenv.base.h"
 #include "gcenv.os.h"
 
-#ifndef FEATURE_STANDALONE_GC
- #error "A GC-private implementation of GCToOSInterface should only be used with FEATURE_STANDALONE_GC"
-#endif // FEATURE_STANDALONE_GC
+#ifndef BUILD_AS_STANDALONE
+ #error "A GC-private implementation of GCToOSInterface should only be used with BUILD_AS_STANDALONE"
+#endif // BUILD_AS_STANDALONE
 
 #if HAVE_SYS_TIME_H
  #include <sys/time.h>
diff --git a/src/gc/wks/CMakeLists.txt b/src/gc/wks/CMakeLists.txt
deleted file mode 100644
index fcb95a385e..0000000000
--- a/src/gc/wks/CMakeLists.txt
+++ /dev/null
@@ -1 +0,0 @@
-add_library_clr(gc_wks STATIC ${GC_SOURCES_WKS})