[PATCH 2/2] Documentation Update.

[Qing Zhao <qing.zhao@oracle.com>]

Update documentation to clarify a GCC extension on structure with
flexible array member being nested in another structure.

gcc/ChangeLog:

	* doc/extend.texi: Document GCC extension on a structure containing
	a flexible array member to be a member of another structure.
---
 gcc/doc/extend.texi | 35 ++++++++++++++++++++++++++++++++++-
 1 file changed, 34 insertions(+), 1 deletion(-)

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4a89a3eae7c..54e4baf49a9 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -1748,7 +1748,40 @@ Flexible array members may only appear as the last member of a
 A structure containing a flexible array member, or a union containing
 such a structure (possibly recursively), may not be a member of a
 structure or an element of an array.  (However, these uses are
-permitted by GCC as extensions.)
+permitted by GCC as extensions, see details below.)
+@end itemize
+
+GCC extension accepts a structure containing a flexible array member, or
+a union containing such a structure (possibly recursively) to be a member
+of a structure.
+
+There are two situations:
+
+@itemize @bullet
+@item
+The structure with a flexible array member is the last field of another
+structure, for example:
+
+@smallexample
+struct flex  @{ int length; char data[]; @};
+
+struct out_flex @{ int m; struct flex flex_data; @};
+@end smallexample
+
+In the above, @code{flex_data.data[]} is considered as a flexible array too.
+
+@item
+The structure with a flexible array member is the middle field of another
+structure, for example:
+
+@smallexample
+struct flex  @{ int length; char data[]; @};
+
+struct mid_flex @{ int m; struct flex flex_data; int n; @};
+@end smallexample
+
+In the above, @code{flex_data.data[]} is allowed to be extended flexibly to
+the padding. E.g, up to 4 elements.
 @end itemize
 
 Non-empty initialization of zero-length
-- 
2.31.1