From: David Faust <david.faust@oracle.com>
To: binutils@sourceware.org
Subject: [PATCH] bpf: use the expected instruction for NOPs
Date: Mon, 14 Sep 2020 12:48:41 -0700 [thread overview]
Message-ID: <20200914194841.163176-1-david.faust@oracle.com> (raw)
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
next reply other threads:[~2020-09-14 19:49 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 19:48 David Faust [this message]
2020-09-15 9:37 ` Nick Clifton
2020-09-15 16:18 ` David Faust
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