extend.texi: add note about reserved ctor/dtor priorities

gcc/Changelog:

	* doc/extend.texi: Add note about reserved priorities
	to the constructor attribute.

Signed-off-by: Jonathan Yong <10walls@gmail.com>

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 49df8e6..251a103 100644 (file)
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -2787,16 +2787,16 @@ On some targets the attributes also accept an integer argument to
 specify a priority to control the order in which constructor and
 destructor functions are run.  A constructor
 with a smaller priority number runs before a constructor with a larger
-priority number; the opposite relationship holds for destructors.  So,
-if you have a constructor that allocates a resource and a destructor
-that deallocates the same resource, both functions typically have the
-same priority.  The priorities for constructor and destructor
-functions are the same as those specified for namespace-scope C++
-objects (@pxref{C++ Attributes}).  However, at present, the order in which
-constructors for C++ objects with static storage duration and functions
-decorated with attribute @code{constructor} are invoked is unspecified.
-In mixed declarations, attribute @code{init_priority} can be used to
-impose a specific ordering.
+priority number; the opposite relationship holds for destructors.  Note
+that priorities 0-100 are reserved.  So, if you have a constructor that
+allocates a resource and a destructor that deallocates the same
+resource, both functions typically have the same priority.  The
+priorities for constructor and destructor functions are the same as
+those specified for namespace-scope C++ objects (@pxref{C++ Attributes}).
+However, at present, the order in which constructors for C++ objects
+with static storage duration and functions decorated with attribute
+@code{constructor} are invoked is unspecified. In mixed declarations,
+attribute @code{init_priority} can be used to impose a specific ordering.
 
 Using the argument forms of the @code{constructor} and @code{destructor}
 attributes on targets where the feature is not supported is rejected with