gas: support .half, .word and .dword directives in eBPF

This little patch adds support to the eBPF port of GAS for a few data
directives.  The names for the directives have been chosen to be
coherent with the suffixes used in eBPF instructions: b, h, w and dw
for 8, 16, 32 and 64-bit values respectively.

Documentation and tests included.
Tested in a x86_64 host.

gas/ChangeLog:

2019-07-17  Jose E. Marchesi  <jose.marchesi@oracle.com>

	* config/tc-bpf.c (md_pseudo_table): .half, .word and .dword.
	* testsuite/gas/bpf/data.s: New file.
	* testsuite/gas/bpf/data.d: Likewise.
	* testsuite/gas/bpf/data-be.d: Likewise.
	* testsuite/gas/bpf/bpf.exp: Run data and data-be.
	* doc/c-bpf.texi (BPF Directives): New section.

1 files changed, 23 insertions, 0 deletions

diff --git a/gas/doc/c-bpf.texi b/gas/doc/c-bpf.texi
index 13f41441caa..9496359f242 100644
--- a/gas/doc/c-bpf.texi
+++ b/gas/doc/c-bpf.texi
@@ -17,6 +17,7 @@
 @menu
 * BPF Options::                 Options
 * BPF Syntax::		        Syntax
+* BPF Directives::		Machine Directives
 * BPF Opcodes::			Opcodes
 @end menu
 
@@ -104,6 +105,28 @@ descriptor @samp{2} in register @samp{r1} we would do:
         lddw %r1, %map_fd(2)
 @end smallexample
 
+@node BPF Directives
+@section Machine Directives
+
+@cindex machine directives, BPF
+
+The BPF version of @code{@value{AS}} supports the following additional
+machine directives:
+
+@table @code
+@cindex @code{half} directive, BPF
+@item .word
+The @code{.half} directive produces a 16 bit value.
+
+@cindex @code{word} directive, BPF
+@item .word
+The @code{.word} directive produces a 32 bit value.
+
+@cindex @code{dword} directive, BPF
+@item .dword
+The @code{.dword} directive produces a 64 bit value.
+@end table
+
 @node BPF Opcodes
 @section Opcodes