thread_pthread.c: precise stack size

* thread_pthread.c (ruby_init_stack): round stack limit to page size
  boundary to calculate stack size more precisely.  [ruby-dev:46174]
  [Bug ruby#7084]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37080 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Thu Oct  4 11:43:28 2012  Nobuyoshi Nakada  <[email protected]>
+
+	* thread_pthread.c (ruby_init_stack): round stack limit to page size
+	  boundary to calculate stack size more precisely.  [ruby-dev:46174]
+	  [Bug #7084]
+
 Wed Oct  3 19:51:57 2012  Narihiro Nakamura  <[email protected]>
 
 	* gc.c: Use the non-recursive marking instead of recursion. The

thread_pthread.c

@@ -649,14 +649,22 @@ ruby_init_stack(volatile VALUE *addr
 	STACK_GROW_DIR_DETECTION;
 	get_stack(&stackaddr, &size);
 	space = STACK_DIR_UPPER((char *)addr - (char *)stackaddr, (char *)stackaddr - (char *)addr);
+	native_main_thread.stack_maxsize = size - space;
 #elif defined(HAVE_GETRLIMIT)
+	int pagesize = getpagesize();
 	struct rlimit rlim;
 	if (getrlimit(RLIMIT_STACK, &rlim) == 0) {
 	    size = (size_t)rlim.rlim_cur;
 	}
-	space = size > 5 * 1024 * 1024 ? 1024 * 1024 : size / 5;
+	addr = native_main_thread.stack_start;
+	if (IS_STACK_DIR_UPPER()) {
+	    space = ((size_t)((char *)addr + size) / pagesize) * pagesize - (size_t)addr;
+	}
+	else {
+	    space = (size_t)addr - ((size_t)((char *)addr - size) / pagesize + 1) * pagesize;
+	}
+	native_main_thread.stack_maxsize = space;
 #endif
-	native_main_thread.stack_maxsize = size - space;
     }
 }