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bpf, riscv: Optimize FROM_LE using verifier_zext on RV64

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This patch adds two optimizations for BPF_ALU BPF_END BPF_FROM_LE in
the RV64 BPF JIT.

First, it enables the verifier zero-extension optimization to avoid zero
extension when imm == 32. Second, it avoids generating code for imm ==
64, since it is equivalent to a no-op.

Co-developed-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Luke Nelson <luke.r.nels@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Björn Töpel <bjorn.topel@gmail.com>
Acked-by: Björn Töpel <bjorn.topel@gmail.com>
Link: https://lore.kernel.org/bpf/20200506000320.28965-3-luke.r.nels@gmail.com
This commit is contained in:
Luke Nelson 2020-05-05 17:03:18 -07:00 committed by Daniel Borkmann
parent 0224b2acea
commit 21a099abb7
1 changed files with 14 additions and 6 deletions
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20
arch/riscv/net/bpf_jit_comp64.c
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@ -542,13 +542,21 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
/* dst = BSWAP##imm(dst) */
case BPF_ALU | BPF_END | BPF_FROM_LE:
{
int shift = 64 - imm;
emit(rv_slli(rd, rd, shift), ctx);
emit(rv_srli(rd, rd, shift), ctx);
switch (imm) {
case 16:
emit(rv_slli(rd, rd, 48), ctx);
emit(rv_srli(rd, rd, 48), ctx);
break;
case 32:
if (!aux->verifier_zext)
emit_zext_32(rd, ctx);
break;
case 64:
/* Do nothing */
break;
}
break;
}
case BPF_ALU | BPF_END | BPF_FROM_BE:
emit(rv_addi(RV_REG_T2, RV_REG_ZERO, 0), ctx);