value.h: reconstruct mrb_ro_data_p().

* use predefined `mrb_ro_data_p()` for user-mode Linux and macOS
* define `MRB_LINK_TIME_RO_DATA_P` if predefined one is used
* configure macro `MRB_USE_LINK_TIME_RO_DATA_P` is no longer used
* contributions for new platforms are welcome

doc/guides/mrbconf.md

@@ -151,14 +151,6 @@ largest value of required alignment.
 
 ## Reduce heap memory configuration
 
-`MRB_USE_LINK_TIME_RO_DATA_P`
-
-* Only available on ELF platforms.
-* If you specify the address of a read-only section when creating a symbol or string, that string will be used as it is.
-* Heap memory can be saved.
-* Uses `__ehdr_start` and `__init_array_start`.
-* It must be `__ehdr_start < data_addr < __init_array_start`.
-
 `MRB_USE_CUSTOM_RO_DATA_P`
 
 * Takes precedence over `MRB_USE_LINK_TIME_RO_DATA_P`.

include/mrbconf.h

@@ -113,11 +113,7 @@
 /* number of object per heap page */
 //#define MRB_HEAP_PAGE_SIZE 1024
 
-/* if __ehdr_start is available, mruby can reduce memory used by symbols */
-//#define MRB_USE_LINK_TIME_RO_DATA_P
-
-/* if MRB_USE_LINK_TIME_RO_DATA_P does not work,
-   you can try mrb_ro_data_p() that you have implemented yourself in any file;
+/* you can provide and use mrb_ro_data_p() for your platform.
    prototype is `mrb_bool mrb_ro_data_p(const char *ptr)` */
 //#define MRB_USE_CUSTOM_RO_DATA_P
 

include/mruby/value.h

@@ -408,17 +408,11 @@ mrb_undef_value(void)
   return v;
 }
 
-#if defined(MRB_USE_ETEXT_EDATA) && !defined(MRB_USE_LINK_TIME_RO_DATA_P)
-# ifdef __GNUC__
-#  warning MRB_USE_ETEXT_EDATA is deprecated. Define MRB_USE_LINK_TIME_RO_DATA_P instead.
-# endif
-# define MRB_USE_LINK_TIME_RO_DATA_P
-#endif
-
 #if defined(MRB_USE_CUSTOM_RO_DATA_P)
 /* If you define `MRB_USE_CUSTOM_RO_DATA_P`, you must implement `mrb_ro_data_p()`. */
 mrb_bool mrb_ro_data_p(const char *p);
-#elif defined(MRB_USE_LINK_TIME_RO_DATA_P) || defined(__linux__)
+#elif (defined(__linux__) && !defined(__KERNEL__))
+#define MRB_LINK_TIME_RO_DATA_P
 extern char __ehdr_start[];
 extern char __init_array_start[];
 
@@ -428,6 +422,7 @@ mrb_ro_data_p(const char *p)
   return __ehdr_start < p && p < __init_array_start;
 }
 #elif defined(__APPLE__)
+#define MRB_LINK_TIME_RO_DATA_P
 #include <mach-o/getsect.h>
 static inline mrb_bool
 mrb_ro_data_p(const char *p)

src/load.c

@@ -606,7 +606,8 @@ read_irep(mrb_state *mrb, const uint8_t *bin, size_t bufsize, uint8_t flags)
 static struct RProc*
 mrb_proc_read_irep(mrb_state *mrb, const uint8_t *bin)
 {
-#if defined(MRB_USE_LINK_TIME_RO_DATA_P) || defined(MRB_USE_CUSTOM_RO_DATA_P)
+  /* MRB_LINK_TIME_RO_DATA_P is defined when predefined mrb_ro_data_p() is used */
+#if defined(MRB_LINK_TIME_RO_DATA_P) || defined(MRB_USE_CUSTOM_RO_DATA_P)
   uint8_t flags = mrb_ro_data_p((char*)bin) ? FLAG_SRC_STATIC : FLAG_SRC_MALLOC;
 #else
   uint8_t flags = FLAG_SRC_STATIC;