bpf, arm: Optimize ALU ARSH K using asr immediate instruction (c648c9c7) · Commits · 戴 / test

This patch adds an optimization that uses the asr immediate instruction for BPF_ALU BPF_ARSH BPF_K, rather than loading the immediate to a temporary register. This is similar to existing code for handling BPF_ALU BPF_{LSH,RSH} BPF_K. This optimization saves two instructions and is more consistent with LSH and RSH. Example of the code generated for BPF_ALU32_IMM(BPF_ARSH, BPF_REG_0, 5) before the optimization: 2c: mov r8, #5 30: mov r9, #0 34: asr r0, r0, r8 and after optimization: 2c: asr r0, r0, #5 Tested on QEMU using lib/test_bpf and test_verifier. Co-developed-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> Link: https://lore.kernel.org/bpf/20200501020210.32294-3-luke.r.nels@gmail.com

arch/arm/net/bpf_jit_32.c

+7 −3

Original line number	Diff line number	Diff line
		@@ -795,6 +795,9 @@ static inline void emit_a32_alu_i(const s8 dst, const u32 val,
		case BPF_RSH:
		emit(ARM_LSR_I(rd, rd, val), ctx);
		break;
		case BPF_ARSH:
		emit(ARM_ASR_I(rd, rd, val), ctx);
		break;
		case BPF_NEG:
		emit(ARM_RSB_I(rd, rd, val), ctx);
		break;
		@@ -1408,7 +1411,6 @@ static int build_insn(const struct bpf_insn insn, struct jit_ctx ctx)
		case BPF_ALU \| BPF_MUL \| BPF_X:
		case BPF_ALU \| BPF_LSH \| BPF_X:
		case BPF_ALU \| BPF_RSH \| BPF_X:
		case BPF_ALU \| BPF_ARSH \| BPF_K:
		case BPF_ALU \| BPF_ARSH \| BPF_X:
		case BPF_ALU64 \| BPF_ADD \| BPF_K:
		case BPF_ALU64 \| BPF_ADD \| BPF_X:
		@@ -1465,10 +1467,12 @@ static int build_insn(const struct bpf_insn insn, struct jit_ctx ctx)
		case BPF_ALU64 \| BPF_MOD \| BPF_K:
		case BPF_ALU64 \| BPF_MOD \| BPF_X:
		goto notyet;
		/* dst = dst >> imm */
		/* dst = dst << imm */
		case BPF_ALU \| BPF_RSH \| BPF_K:
		/* dst = dst >> imm */
		/* dst = dst >> imm (signed) */
		case BPF_ALU \| BPF_LSH \| BPF_K:
		case BPF_ALU \| BPF_RSH \| BPF_K:
		case BPF_ALU \| BPF_ARSH \| BPF_K:
		if (unlikely(imm > 31))
		return -EINVAL;
		if (imm)

arch/arm/net/bpf_jit_32.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -94,6 +94,9 @@
		#define ARM_INST_LSR_I 0x01a00020
		#define ARM_INST_LSR_R 0x01a00030

		#define ARM_INST_ASR_I 0x01a00040
		#define ARM_INST_ASR_R 0x01a00050

		#define ARM_INST_MOV_R 0x01a00000
		#define ARM_INST_MOVS_R 0x01b00000
		#define ARM_INST_MOV_I 0x03a00000

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