Rename MRB_USE_ETEXT_EDATA to MRB_USE_LINK_TIME_RO_DATA_P and support lld linked programs

In lld linked programs, .rodata comes before .text, thus mrb_ro_data_p
will return false for strings in .rodata. Change the lower bound from
_etext to __ehdr_start to catch these cases. This works for ld.bfd, gold
and lld, and it does not have false positives even if .init_array does
not exist.

Remove the branch that uses _edata: strings in .data can be modified so
this is semantically incorrect. Delete the __APPLE__ branch (its
manpages say get_etext() and get_edata() are strongly discouraged).
.init_array has been adopted by most ELF platforms to supersede .ctors.

Neither _etext nor _edata is used, so rename MRB_USE_ETEXT_EDATA to
MRB_USE_EHDR_START.

2 files changed, 13 insertions, 29 deletions

diff --git a/include/mrbconf.h b/include/mrbconf.h
index c5b9afd05..b86ce82e8 100644
--- a/include/mrbconf.h
+++ b/include/mrbconf.h
@@ -88,14 +88,10 @@
 /* number of object per heap page */
 //#define MRB_HEAP_PAGE_SIZE 1024
 
-/* if _etext and _edata available, mruby can reduce memory used by symbols */
-//#define MRB_USE_ETEXT_EDATA
+/* if __ehdr_start is available, mruby can reduce memory used by symbols */
+//#define MRB_USE_LINK_TIME_RO_DATA_P
 
-/* do not use __init_array_start to determine readonly data section;
-   effective only when MRB_USE_ETEXT_EDATA is defined */
-//#define MRB_NO_INIT_ARRAY_START
-
-/* if do not works both MRB_USE_ETEXT_EDATA and MRB_NO_INIT_ARRAY_START,
+/* 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;
    prototype is `mrb_bool mrb_ro_data_p(const char *ptr)` */
 //#define MRB_USE_CUSTOM_RO_DATA_P
diff --git a/include/mruby/value.h b/include/mruby/value.h
index 52ce93d58..831334b9d 100644
--- a/include/mruby/value.h
+++ b/include/mruby/value.h
@@ -309,37 +309,25 @@ 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_ETEXT_EDATA)
-#if (defined(__APPLE__) && defined(__MACH__))
-#include <mach-o/getsect.h>
-static inline mrb_bool
-mrb_ro_data_p(const char *p)
-{
-  return (const char*)get_etext() < p && p < (const char*)get_edata();
-}
-#else
-extern char _etext[];
-#ifdef MRB_NO_INIT_ARRAY_START
-extern char _edata[];
-
-static inline mrb_bool
-mrb_ro_data_p(const char *p)
-{
-  return _etext < p && p < _edata;
-}
-#else
+#elif defined(MRB_USE_LINK_TIME_RO_DATA_P)
+extern char __ehdr_start[];
 extern char __init_array_start[];
 
 static inline mrb_bool
 mrb_ro_data_p(const char *p)
 {
-  return _etext < p && p < (char*)&__init_array_start;
+  return __ehdr_start < p && p < __init_array_start;
 }
-#endif
-#endif
 #else
 # define mrb_ro_data_p(p) FALSE
 #endif