Pass string error buffer into dln_open

On Windows, the error exists on the stack so we should pass an error
buffer from the caller.

dln.c

@@ -194,7 +194,6 @@ dln_strerror(char *message, size_t size)
     }
     return message;
 }
-#define dln_strerror() dln_strerror(message, sizeof message)
 #elif defined USE_DLN_DLOPEN
 static const char *
 dln_strerror(void)
@@ -340,14 +339,12 @@ dln_disable_dlclose(void)
 
 #if defined(_WIN32) || defined(USE_DLN_DLOPEN)
 void *
-dln_open(const char *file, const char **error)
+dln_open(const char *file, char *error, size_t size)
 {
     static const char incompatible[] = "incompatible library version";
     void *handle;
 
 #if defined(_WIN32)
-    char message[1024];
-
     /* Convert the file path to wide char */
     WCHAR *winfile = rb_w32_mbstr_to_wstr(CP_UTF8, file, -1, NULL);
     if (!winfile) {
@@ -359,14 +356,14 @@ dln_open(const char *file, const char **error)
     free(winfile);
 
     if (!handle) {
-        *error = dln_strerror();
+        strlcpy(error, dln_strerror(error, size), size);
         return NULL;
     }
 
 # if defined(RUBY_EXPORT)
     if (!rb_w32_check_imported(handle, rb_libruby_handle())) {
         FreeLibrary(handle);
-        *error = incompatible;
+        strlcpy(error, incompatible, size);
         return NULL;
     }
 # endif
@@ -386,7 +383,7 @@ dln_open(const char *file, const char **error)
     /* Load file */
     handle = dlopen(file, RTLD_LAZY|RTLD_GLOBAL);
     if (handle == NULL) {
-        *error = dln_strerror();
+        strlcpy(error, dln_strerror(), size);
         return NULL;
     }
 
@@ -409,10 +406,14 @@ dln_open(const char *file, const char **error)
                     libruby_name = tmp;
                 }
                 dlclose(handle);
+
                 if (libruby_name) {
-                    dln_loaderror("linked to incompatible %s - %s", libruby_name, file);
+                    snprintf(error, size, "linked to incompatible %s - %s", libruby_name, file);
                 }
-                *error = incompatible;
+                else {
+                    strlcpy(error, incompatible, size);
+                }
+
                 return NULL;
             }
         }
@@ -442,7 +443,7 @@ dln_sym_func(void *handle, const char *symbol)
         const char *error;
 #if defined(_WIN32)
         char message[1024];
-        error = dln_strerror();
+        error = dln_strerror(message, sizeof(message));
 #elif defined(USE_DLN_DLOPEN)
         const size_t errlen = strlen(error = dln_strerror()) + 1;
         error = memcpy(ALLOCA_N(char, errlen), error, errlen);
@@ -497,8 +498,8 @@ void *
 dln_load(const char *file)
 {
 #if defined(_WIN32) || defined(USE_DLN_DLOPEN)
-    const char *error = NULL;
-    void *handle = dln_open(file, &error);
+    char error[1024];
+    void *handle = dln_open(file, error, sizeof(error));
 
     if (handle == NULL) {
         dln_loaderror("%s - %s", error, file);

dln.h

@@ -25,7 +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, const char **error);
+void *dln_open(const char *file, char *error, size_t size);
 void *dln_symbol(void*,const char*);
 
 RUBY_SYMBOL_EXPORT_END

dmydln.c

@@ -21,9 +21,9 @@ dln_symbol(void *handle, const char *symbol)
     UNREACHABLE_RETURN(NULL);
 }
 
-NORETURN(void *dln_open(const char *library, const char **error));
+NORETURN(void *dln_open(const char *library, char *error, size_t size));
 void*
-dln_open(const char *library, const char **error)
+dln_open(const char *library, char *error, size_t size)
 {
     rb_loaderror("this executable file can't load extension libraries");
 

gc.c

@@ -1896,8 +1896,8 @@ ruby_external_gc_init()
     char *gc_so_path = getenv("RUBY_GC_LIBRARY_PATH");
     void *handle = NULL;
     if (gc_so_path) {
-        const char *error = NULL;
-        handle = dln_open(gc_so_path, &error);
+        char error[128];
+        handle = dln_open(gc_so_path, error, sizeof(error));
         if (!handle) {
             rb_bug("ruby_external_gc_init: Shared library %s cannot be opened (%s)", gc_so_path, error);
         }