Document .Nbyte assembler directives

* doc/as.texinfo (2byte, 4byte, 8byte): Document.
	* doc/c-arm.texi (2byte, 4byte, 8byte): Omit if ELF.

gas/ChangeLog

@@ -1,3 +1,9 @@
+2017-03-07  Tobin C. Harding  <me@tobin.cc>
+	    Alan Modra  <amodra@gmail.com>
+
+	* doc/as.texinfo (2byte, 4byte, 8byte): Document.
+	* doc/c-arm.texi (2byte, 4byte, 8byte): Omit if ELF.
+
 2017-03-06  H.J. Lu  <hongjiu.lu@intel.com>
 
 	* config/tc-i386.c (cpu_arch): Add .cet.

gas/doc/as.texinfo

@@ -4555,6 +4555,11 @@ Some machine configurations provide additional directives.
 @ifclear no-space-dir
 * Zero::                        @code{.zero @var{size}}
 @end ifclear
+@ifset ELF
+* 2byte::                       @code{.2byte @var{expressions}}
+* 4byte::                       @code{.4byte @var{expressions}}
+* 8byte::                       @code{.8byte @var{bignums}}
+@end ifset
 * Deprecated::                  Deprecated Directives
 @end menu
 
@@ -7333,6 +7338,39 @@ so in can take an optional second argument of the value to store in the bytes
 instead of zero.  Using @samp{.zero} in this way would be confusing however.
 @end ifclear
 
+@ifset ELF
+@node 2byte
+@cindex @code{2byte} directive
+@cindex two-byte integer
+@cindex integer, 2-byte
+@section @code{.2byte @var{expression} [, @var{expression}]*}
+
+This directive @code{.2byte}, which is available for ELF targets, expects zero
+or more expressions, separated by commas. Each expression is assembled into the
+next two bytes.
+
+@node 4byte
+@cindex @code{4byte} directive
+@cindex four-byte integer
+@cindex integer, 4-byte
+@section @code{.4byte @var{expression} [, @var{expression}]*}
+
+This directive @code{.4byte}, which is available for ELF targets, expects zero
+or more expressions, separated by commas. Each expression is assembled into the
+next four bytes.
+
+@node 8byte
+@cindex @code{8byte} directive
+@cindex eight-byte integer
+@cindex integer, 8-byte
+@section @code{.8byte @var{expression} [, @var{expression}]*}
+
+This directive @code{.8byte}, which is available for ELF targets, expects zero
+or more bignums, separated by commas.  For each bignum, it emits
+an 8-byte integer.  If the bignum won't fit in 8 bytes, it prints a
+warning message; and just takes the lowest order 8 bytes of the bignum.
+@end ifset
+
 @node Deprecated
 @section Deprecated Directives
 

gas/doc/c-arm.texi

@@ -594,6 +594,7 @@ The ARM family uses @sc{ieee} floating-point numbers.
 
 @c AAAAAAAAAAAAAAAAAAAAAAAAA
 
+@ifclear ELF
 @cindex @code{.2byte} directive, ARM
 @cindex @code{.4byte} directive, ARM
 @cindex @code{.8byte} directive, ARM
@@ -601,6 +602,7 @@ The ARM family uses @sc{ieee} floating-point numbers.
 @itemx .4byte @var{expression} [, @var{expression}]*
 @itemx .8byte @var{expression} [, @var{expression}]*
 These directives write 2, 4 or 8 byte values to the output section.
+@end ifclear
 
 @cindex @code{.align} directive, ARM
 @item .align @var{expression} [, @var{expression}]