netdev - [PATCH 3/3] powerpc: bpf: implement in-register swap for 64-bit endian operations

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Date:   Fri, 13 Jan 2017 22:40:02 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     mpe@...erman.id.au
Cc:     linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, davem@...emloft.net
Subject: [PATCH 3/3] powerpc: bpf: implement in-register swap for 64-bit endian operations

Generate instructions to perform the endian conversion using registers,
rather than generating two memory accesses.

The "way easier and faster" comment was obviously for the author, not
the processor.

Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
 arch/powerpc/net/bpf_jit_comp64.c | 22 ++++++++++++++--------
 1 file changed, 14 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/net/bpf_jit_comp64.c b/arch/powerpc/net/bpf_jit_comp64.c
index 1e313db..0413a89 100644
--- a/arch/powerpc/net/bpf_jit_comp64.c
+++ b/arch/powerpc/net/bpf_jit_comp64.c
@@ -599,16 +599,22 @@ static int bpf_jit_build_body(struct bpf_prog *fp, u32 *image,
 				break;
 			case 64:
 				/*
-				 * Way easier and faster(?) to store the value
-				 * into stack and then use ldbrx
+				 * We'll split it up into two words, swap those
+				 * independently and then merge them back.
 				 *
-				 * ctx->seen will be reliable in pass2, but
-				 * the instructions generated will remain the
-				 * same across all passes
+				 * First up, let's swap the most-significant word.
 				 */
-				PPC_STD(dst_reg, 1, bpf_jit_stack_local(ctx));
-				PPC_ADDI(b2p[TMP_REG_1], 1, bpf_jit_stack_local(ctx));
-				PPC_LDBRX(dst_reg, 0, b2p[TMP_REG_1]);
+				PPC_RLDICL(b2p[TMP_REG_1], dst_reg, 32, 32);
+				PPC_RLWINM(b2p[TMP_REG_2], b2p[TMP_REG_1], 8, 0, 31);
+				PPC_RLWIMI(b2p[TMP_REG_2], b2p[TMP_REG_1], 24, 0, 7);
+				PPC_RLWIMI(b2p[TMP_REG_2], b2p[TMP_REG_1], 24, 16, 23);
+				/* Then, the second half */
+				PPC_RLWINM(b2p[TMP_REG_1], dst_reg, 8, 0, 31);
+				PPC_RLWIMI(b2p[TMP_REG_1], dst_reg, 24, 0, 7);
+				PPC_RLWIMI(b2p[TMP_REG_1], dst_reg, 24, 16, 23);
+				/* Merge back */
+				PPC_RLDICR(dst_reg, b2p[TMP_REG_1], 32, 31);
+				PPC_OR(dst_reg, dst_reg, b2p[TMP_REG_2]);
 				break;
 			}
 			break;
-- 
2.10.2