Initialize external GC Library

Co-Authored-By: Peter Zhu <peter@peterzhu.ca>

dln.c

@@ -339,7 +339,7 @@ dln_disable_dlclose(void)
 #endif
 
 #if defined(_WIN32) || defined(USE_DLN_DLOPEN)
-static void *
+void *
 dln_open(const char *file)
 {
     static const char incompatible[] = "incompatible library version";
@@ -427,7 +427,7 @@ dln_open(const char *file)
     dln_loaderror("%s - %s", error, file);
 }
 
-static void *
+void *
 dln_sym(void *handle, const char *symbol)
 {
 #if defined(_WIN32)

dln.h

@@ -25,6 +25,7 @@ RUBY_SYMBOL_EXPORT_BEGIN
 char *dln_find_exe_r(const char*,const char*,char*,size_t DLN_FIND_EXTRA_ARG_DECL);
 char *dln_find_file_r(const char*,const char*,char*,size_t DLN_FIND_EXTRA_ARG_DECL);
 void *dln_load(const char*);
+void *dln_open(const char *file);
 void *dln_symbol(void*,const char*);
 
 RUBY_SYMBOL_EXPORT_END

dmydln.c

@@ -20,3 +20,13 @@ dln_symbol(void *handle, const char *symbol)
 
     UNREACHABLE_RETURN(NULL);
 }
+
+NORETURN(void *dln_open(const char*));
+void*
+dln_open(const char *library)
+{
+    rb_loaderror("this executable file can't load extension libraries");
+
+    UNREACHABLE_RETURN(NULL);
+}
+

gc.c

@@ -1884,6 +1884,55 @@ rb_gc_initial_stress_set(VALUE flag)
     initial_stress = flag;
 }
 
+static void * Alloc_GC_impl(void);
+
+#if USE_SHARED_GC
+# include "dln.h"
+# define Alloc_GC rb_gc_functions->init
+
+void
+ruby_external_gc_init()
+{
+    rb_gc_function_map_t *map = malloc(sizeof(rb_gc_function_map_t));
+    rb_gc_functions = map;
+
+    char *gc_so_path = getenv("RUBY_GC_LIBRARY_PATH");
+    if (!gc_so_path) {
+        map->init = Alloc_GC_impl;
+        return;
+    }
+
+    void *h = dln_open(gc_so_path);
+    if (!h) {
+        rb_bug(
+            "ruby_external_gc_init: Shared library %s cannot be opened.",
+            gc_so_path
+        );
+    }
+
+    void *gc_init_func = dln_symbol(h, "Init_GC");
+    if (!gc_init_func) {
+        rb_bug(
+            "ruby_external_gc_init: Init_GC func not exported by library %s",
+            gc_so_path
+        );
+    }
+
+    map->init = gc_init_func;
+}
+#else
+# define Alloc_GC Alloc_GC_impl
+#endif
+
+rb_objspace_t *
+rb_objspace_alloc(void)
+{
+#if USE_SHARED_GC
+    ruby_external_gc_init();
+#endif
+    return (rb_objspace_t *)Alloc_GC();
+}
+
 static void free_stack_chunks(mark_stack_t *);
 static void mark_stack_free_cache(mark_stack_t *);
 static void heap_page_free(rb_objspace_t *objspace, struct heap_page *page);
@@ -3489,8 +3538,8 @@ static const struct st_hash_type object_id_hash_type = {
     object_id_hash,
 };
 
-rb_objspace_t *
-rb_objspace_alloc(void)
+static void *
+Alloc_GC_impl(void)
 {
     rb_objspace_t *objspace = calloc1(sizeof(rb_objspace_t));
     ruby_current_vm_ptr->objspace = objspace;

internal/gc.h

@@ -16,6 +16,10 @@
 #include "ruby/ruby.h"          /* for rb_event_flag_t */
 #include "vm_core.h"            /* for GET_EC() */
 
+#ifndef USE_SHARED_GC
+# define USE_SHARED_GC 0
+#endif
+
 #if defined(__x86_64__) && !defined(_ILP32) && defined(__GNUC__)
 #define SET_MACHINE_STACK_END(p) __asm__ __volatile__ ("movq\t%%rsp, %0" : "=r" (*(p)))
 #elif defined(__i386) && defined(__GNUC__)

vm_core.h

@@ -106,6 +106,14 @@ extern int ruby_assert_critical_section_entered;
 
 #include "ruby/thread_native.h"
 
+#if USE_SHARED_GC
+typedef struct gc_function_map {
+    void *(*init)(void);
+} rb_gc_function_map_t;
+
+#define rb_gc_functions (GET_VM()->gc_functions_map)
+#endif
+
 /*
  * implementation selector of get_insn_info algorithm
  *   0: linear search
@@ -752,6 +760,9 @@ typedef struct rb_vm_struct {
     int coverage_mode;
 
     struct rb_objspace *objspace;
+#if USE_SHARED_GC
+    rb_gc_function_map_t *gc_functions_map;
+#endif
 
     rb_at_exit_list *at_exit;