[bpf-next,2/4] bpf, riscv: Optimize FROM_LE using verifier_zext on RV64

Commit Message

Luke Nelson May 6, 2020, 12:03 a.m. UTC

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 <[e-mail]>
Signed-off-by: Xi Wang <[e-mail]>
Signed-off-by: Luke Nelson <[e-mail]>
---
 arch/riscv/net/bpf_jit_comp64.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

Patch

diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index e2636902a74e..c3ce9a911b66 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -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);