gas: support double-slash line comments in BPF assembly

This patch makes the BPF assembler to support double-slash line
comments, like the llvm BPF assembler does.  At this point both
assemblers support the same commenting styles:

- Line comments preceded by # or //.
- Non-nestable block comments delimited by /* and */.

This patch also adds a couple of tests to make sure all the comment
styles work in both normal and pseudoc syntax.  The manual is also
updated to mention double-slash line comments.

gas/ChangeLog

@@ -1,3 +1,14 @@
+2023-11-30  Jose E. Marchesi  <jose.marchesi@oracle.com>
+
+	* config/tc-bpf.h (DOUBLESLASH_LINE_COMMENTS): Define.
+	* testsuite/gas/bpf/comments.s: New file.
+	* testsuite/gas/bpf/comments.d: Likewise.
+	* testsuite/gas/bpf/comments-pseudoc.d: Likewise.
+	* testsuite/gas/bpf/comments-pseudoc.s: Likewise.
+	* testsuite/gas/bpf/bpf.exp: Run comments and comments-pseudoc.
+	* doc/c-bpf.texi (BPF Special Characters): Document // comments.
+	* NEWS: Update.
+
 2023-11-28  Jose E. Marchesi  <jose.marchesi@oracle.com>
 
 	* NEWS: Add entry about change of comment syntax in the BPF

gas/NEWS

@@ -41,6 +41,9 @@
   therefore they cannot longer be used to begin line comments. This matches the
   behavior of the clang/LLVM BPF assembler.
 
+* The BPF assembler now allows using both hash (#) and double slash (//) to
+  begin line comments.
+
 Changes in 2.41:
 
 * Add support for the KVX instruction set.

gas/config/tc-bpf.h

@@ -35,6 +35,9 @@
 #define TARGET_BYTES_BIG_ENDIAN 0
 #endif
 
+/* Permit // comments.  */
+#define DOUBLESLASH_LINE_COMMENTS 1
+
 /* .-foo gets turned into PC relative relocs.  */
 #define DIFF_EXPR_OK    1
 

gas/doc/c-bpf.texi

@@ -68,8 +68,8 @@ the host endianness is used.
 
 @cindex line comment character, BPF
 @cindex BPF line comment character
-The presence of a @samp{#} on a line indicates the start of a comment
-that extends to the end of the current line.
+The presence of a @samp{#} or @samp{//} anywhere on a line indicates
+the start of a comment that extends to the end of the line.
 
 @cindex block comments, BPF
 @cindex BPF block comments

gas/testsuite/gas/bpf/bpf.exp

@@ -18,6 +18,10 @@
 # Foundation, Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  
 
 if {[istarget bpf*-*-*]} {
+    # Misc tests.
+    run_dump_test comments
+    run_dump_test comments-pseudoc
+
     # Little-endian BPF tests
     run_dump_test call
     run_dump_test exit

gas/testsuite/gas/bpf/comments-pseudoc.d

@@ -0,0 +1,12 @@
+#as: -EL -mdialect=pseudoc
+#objdump: -dr -M hex
+#name: BPF assembler comments - pseudoc
+
+.*: +file format .*bpf.*
+
+Disassembly of section .text:
+
+[0-9a-f]+ <.*>:
+   0:	07 02 00 00 9a 02 00 00 	add %r2,0x29a
+   8:	07 03 00 00 66 fd ff ff 	add %r3,0xfffffd66
+  10:	07 04 00 00 ef be ad 7e 	add %r4,0x7eadbeef

gas/testsuite/gas/bpf/comments-pseudoc.s

@@ -0,0 +1,5 @@
+# This is a comment
+        r2 += 666 # This is also a comment
+        r3 += -666 /* So is
+this */
+        r4 += 0x7eadbeef // And this

gas/testsuite/gas/bpf/comments.d

@@ -0,0 +1,12 @@
+#as: -EL -mdialect=normal
+#objdump: -dr -M hex
+#name: BPF assembler comments
+
+.*: +file format .*bpf.*
+
+Disassembly of section .text:
+
+[0-9a-f]+ <.*>:
+   0:	07 02 00 00 9a 02 00 00 	add %r2,0x29a
+   8:	07 03 00 00 66 fd ff ff 	add %r3,0xfffffd66
+  10:	07 04 00 00 ef be ad 7e 	add %r4,0x7eadbeef

gas/testsuite/gas/bpf/comments.s

@@ -0,0 +1,5 @@
+# This is a comment
+        add %r2, 666 # This is also a comment
+        add %r3, -666 /* So is
+this */
+        add %r4, 0x7eadbeef // And this