netdev - [PATCH bpf-next 01/13] bpf: xor of a/x in cbpf can be done in 32 bit alu

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Date:   Fri, 26 Jan 2018 23:33:36 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     ast@...nel.org
Cc:     netdev@...r.kernel.org, Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH bpf-next 01/13] bpf: xor of a/x in cbpf can be done in 32 bit alu

Very minor optimization; saves 1 byte per program in x86_64
JIT in cBPF prologue.

Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Alexei Starovoitov <ast@...nel.org>
---
 net/core/filter.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 18da42a..cba2f73 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -401,8 +401,8 @@ static int bpf_convert_filter(struct sock_filter *prog, int len,
 		/* Classic BPF expects A and X to be reset first. These need
 		 * to be guaranteed to be the first two instructions.
 		 */
-		*new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_A, BPF_REG_A);
-		*new_insn++ = BPF_ALU64_REG(BPF_XOR, BPF_REG_X, BPF_REG_X);
+		*new_insn++ = BPF_ALU32_REG(BPF_XOR, BPF_REG_A, BPF_REG_A);
+		*new_insn++ = BPF_ALU32_REG(BPF_XOR, BPF_REG_X, BPF_REG_X);
 
 		/* All programs must keep CTX in callee saved BPF_REG_CTX.
 		 * In eBPF case it's done by the compiler, here we need to
-- 
2.9.5