[PATCH] bpf: use the expected instruction for NOPs

[David Faust]

The BPF ISA does not have a no-op instruction. There are different ways
to achieve no-op, but in practice the Linux kernel verifier expects a
particular form, namely "ja 0". Update the define md_single_noop_insn
for BPF to reflect this.

For more detail, see the corresponding GCC back end patch:
https://gcc.gnu.org/pipermail/gcc-patches/2020-September/553893.html

gas/
	* config/tc-bpf.h (md_single_noop_insn): Use 'ja 0' for no-op.

---
 gas/config/tc-bpf.h | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/gas/config/tc-bpf.h b/gas/config/tc-bpf.h
index cb02d6c1338..e7e505cfaa5 100644
--- a/gas/config/tc-bpf.h
+++ b/gas/config/tc-bpf.h
@@ -48,4 +48,6 @@
 /* Values passed to md_apply_fix don't include the symbol value.  */
 #define MD_APPLY_SYM_VALUE(FIX) 0
 
-#define md_single_noop_insn "mov %r1,%r1"
+/* The Linux kernel verifier expects NOPs to be encoded in this way;
+   a jump to offset 0 means jump to the next instruction.  */
+#define md_single_noop_insn "ja 0"
-- 
2.26.2