[PATCH] rsb: Clarify Ada build requirements

[Sebastian Huber]

---
 rsb/building-tools-and-rtems.rst | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/rsb/building-tools-and-rtems.rst b/rsb/building-tools-and-rtems.rst
index 5fd5d78..207463c 100644
--- a/rsb/building-tools-and-rtems.rst
+++ b/rsb/building-tools-and-rtems.rst
@@ -29,7 +29,13 @@ Following are currently available:
   Do not build a C++ compiler.
 
 ``--with-ada``
-  Attempt to build an Ada compiler.  You need a native GNAT installed.
+  Attempt to build an Ada compiler.  You need a native GNAT installed.  The GCC
+  major version of the native GNAT must be identical to the major version of
+  the target GCC, e.g. if the target GCC is version 7.3.0, then the native GCC
+  must be use a 7.*.* version.  In the prefix there must not be a previous
+  installation of the tools.  An existing installation can interfere with the
+  build.  Installing new tools over a previous installation may fail due to
+  file permission errors.
 
 ``--with-fortran``
   Attempt to build a Fortran compiler.
-- 
2.16.4