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@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/net/core/filter.c b/net/core/filter.c
index fe2c793..60d8c87 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -401,8 +401,8 @@ do_pass:
                /* 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