From 7d134041a89610ae552501fc88652805addcdee4 Mon Sep 17 00:00:00 2001 From: Jiong Wang Date: Fri, 24 May 2019 23:25:14 +0100 Subject: [PATCH] bpf: introduce new mov32 variant for doing explicit zero extension The encoding for this new variant is based on BPF_X format. "imm" field was 0 only, now it could be 1 which means doing zero extension unconditionally .code = BPF_ALU | BPF_MOV | BPF_X .dst_reg = DST .src_reg = SRC .imm = 1 We use this new form for doing zero extension for which verifier will guarantee SRC == DST. Implications on JIT back-ends when doing code-gen for BPF_ALU | BPF_MOV | BPF_X: 1. No change if hardware already does zero extension unconditionally for sub-register write. 2. Otherwise, when seeing imm == 1, just generate insns to clear high 32-bit. No need to generate insns for the move because when imm == 1, dst_reg is the same as src_reg at the moment. Interpreter doesn't need change as well. It is doing unconditionally zero extension for mov32 already. One helper macro BPF_ZEXT_REG is added to help creating zero extension insn using this new mov32 variant. One helper function insn_is_zext is added for checking one insn is an zero extension on dst. This will be widely used by a few JIT back-ends in later patches in this set. Signed-off-by: Jiong Wang Signed-off-by: Alexei Starovoitov --- include/linux/filter.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/filter.h b/include/linux/filter.h index 7148bab96943..bb10ffb88452 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -160,6 +160,20 @@ struct ctl_table_header; .off = 0, \ .imm = IMM }) +/* Special form of mov32, used for doing explicit zero extension on dst. */ +#define BPF_ZEXT_REG(DST) \ + ((struct bpf_insn) { \ + .code = BPF_ALU | BPF_MOV | BPF_X, \ + .dst_reg = DST, \ + .src_reg = DST, \ + .off = 0, \ + .imm = 1 }) + +static inline bool insn_is_zext(const struct bpf_insn *insn) +{ + return insn->code == (BPF_ALU | BPF_MOV | BPF_X) && insn->imm == 1; +} + /* BPF_LD_IMM64 macro encodes single 'load 64-bit immediate' insn */ #define BPF_LD_IMM64(DST, IMM) \ BPF_LD_IMM64_RAW(DST, 0, IMM) -- 2.30.2