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bpf: xor of a/x in cbpf can be done in 32 bit alu

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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>
This commit is contained in:
Daniel Borkmann 2018-01-26 23:33:36 +01:00 • committed by Alexei Starovoitov
parent c25ef6a5e6
commit 1d621674d9
1 changed files with 2 additions and 2 deletions
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4
net/core/filter.c
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@ -401,8 +401,8 @@ do_pass:
/* Classic BPF expects A and X to be reset first. These need /* Classic BPF expects A and X to be reset first. These need
* to be guaranteed to be the first two instructions. * 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_ALU32_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_X, BPF_REG_X);
/* All programs must keep CTX in callee saved BPF_REG_CTX. /* All programs must keep CTX in callee saved BPF_REG_CTX.
* In eBPF case it's done by the compiler, here we need to * In eBPF case it's done by the compiler, here we need to