[gcc r12-3155] extend.texi: add note about reserved ctor/dtor priorities

[gcc r12-3155] extend.texi: add note about reserved ctor/dtor priorities

[Jonathan Yong]

https://gcc.gnu.org/g:d4b782985b4adb86ebcccff697366136321d45b2

commit r12-3155-gd4b782985b4adb86ebcccff697366136321d45b2
Author: Jonathan Yong <10walls@gmail.com>
Date:   Wed Aug 25 16:36:14 2021 +0000

    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:
---
 gcc/doc/extend.texi | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 49df8e6dc38..251a10302b4 100644
--- 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