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bpf, riscv: Optimize BPF_JMP BPF_K when imm == 0 on RV64

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This patch adds an optimization to BPF_JMP (32- and 64-bit) BPF_K for
when the BPF immediate is zero.

When the immediate is zero, the code can directly use the RISC-V zero
register instead of loading a zero immediate to a temporary register
first.

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/20200506000320.28965-4-luke.r.nels@gmail.com
This commit is contained in:
Luke Nelson 2020-05-05 17:03:19 -07:00 committed by Daniel Borkmann
parent 21a099abb7
commit ca349a6a10
1 changed files with 10 additions and 5 deletions
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15
arch/riscv/net/bpf_jit_comp64.c
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@ -796,7 +796,13 @@ out_be:
case BPF_JMP32 | BPF_JSET | BPF_K:
rvoff = rv_offset(i, off, ctx);
s = ctx->ninsns;
emit_imm(RV_REG_T1, imm, ctx);
if (imm) {
emit_imm(RV_REG_T1, imm, ctx);
rs = RV_REG_T1;
} else {
/* If imm is 0, simply use zero register. */
rs = RV_REG_ZERO;
}
if (!is64) {
if (is_signed_bpf_cond(BPF_OP(code)))
emit_sext_32_rd(&rd, ctx);
@ -811,11 +817,10 @@ out_be:
if (BPF_OP(code) == BPF_JSET) {
/* Adjust for and */
rvoff -= 4;
emit(rv_and(RV_REG_T1, rd, RV_REG_T1), ctx);
emit_branch(BPF_JNE, RV_REG_T1, RV_REG_ZERO, rvoff,
ctx);
emit(rv_and(rs, rd, rs), ctx);
emit_branch(BPF_JNE, rs, RV_REG_ZERO, rvoff, ctx);
} else {
emit_branch(BPF_OP(code), rd, RV_REG_T1, rvoff, ctx);
emit_branch(BPF_OP(code), rd, rs, rvoff, ctx);
}
break;