powerpc/ebpf/jit: Implement JIT compiler for extended BPF

PPC64 eBPF JIT compiler.

Enable with:
  echo 1 > /proc/sys/net/core/bpf_jit_enable
or
  echo 2 > /proc/sys/net/core/bpf_jit_enable

... to see the generated JIT code. This can further be processed with
tools/net/bpf_jit_disasm.

With CONFIG_TEST_BPF=m and 'modprobe test_bpf':

 test_bpf: Summary: 305 PASSED, 0 FAILED, [297/297 JIT'ed]

... on both ppc64 BE and LE.

The details of the approach are documented through various comments in
the code.

Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 102 insertions, 0 deletions

diff --git a/arch/powerpc/net/bpf_jit64.h b/arch/powerpc/net/bpf_jit64.h
new file mode 100644
index 000000000000..5046d6f65c02
--- /dev/null
+++ b/arch/powerpc/net/bpf_jit64.h
@@ -0,0 +1,102 @@
+/*
+ * bpf_jit64.h: BPF JIT compiler for PPC64
+ *
+ * Copyright 2016 Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
+ *		  IBM Corporation
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; version 2
+ * of the License.
+ */
+#ifndef _BPF_JIT64_H
+#define _BPF_JIT64_H
+
+#include "bpf_jit.h"
+
+/*
+ * Stack layout:
+ *
+ *		[	prev sp		] <-------------
+ *		[   nv gpr save area	] 8*8		|
+ * fp (r31) -->	[   ebpf stack space	] 512		|
+ *		[  local/tmp var space	] 16		|
+ *		[     frame header	] 32/112	|
+ * sp (r1) --->	[    stack pointer	] --------------
+ */
+
+/* for bpf JIT code internal usage */
+#define BPF_PPC_STACK_LOCALS	16
+/* for gpr non volatile registers BPG_REG_6 to 10, plus skb cache registers */
+#define BPF_PPC_STACK_SAVE	(8*8)
+/* Ensure this is quadword aligned */
+#define BPF_PPC_STACKFRAME	(STACK_FRAME_MIN_SIZE + BPF_PPC_STACK_LOCALS + \
+				 MAX_BPF_STACK + BPF_PPC_STACK_SAVE)
+
+#ifndef __ASSEMBLY__
+
+/* BPF register usage */
+#define SKB_HLEN_REG	(MAX_BPF_REG + 0)
+#define SKB_DATA_REG	(MAX_BPF_REG + 1)
+#define TMP_REG_1	(MAX_BPF_REG + 2)
+#define TMP_REG_2	(MAX_BPF_REG + 3)
+
+/* BPF to ppc register mappings */
+static const int b2p[] = {
+	/* function return value */
+	[BPF_REG_0] = 8,
+	/* function arguments */
+	[BPF_REG_1] = 3,
+	[BPF_REG_2] = 4,
+	[BPF_REG_3] = 5,
+	[BPF_REG_4] = 6,
+	[BPF_REG_5] = 7,
+	/* non volatile registers */
+	[BPF_REG_6] = 27,
+	[BPF_REG_7] = 28,
+	[BPF_REG_8] = 29,
+	[BPF_REG_9] = 30,
+	/* frame pointer aka BPF_REG_10 */
+	[BPF_REG_FP] = 31,
+	/* eBPF jit internal registers */
+	[SKB_HLEN_REG] = 25,
+	[SKB_DATA_REG] = 26,
+	[TMP_REG_1] = 9,
+	[TMP_REG_2] = 10
+};
+
+/* Assembly helpers */
+#define DECLARE_LOAD_FUNC(func)	u64 func(u64 r3, u64 r4);			\
+				u64 func##_negative_offset(u64 r3, u64 r4);	\
+				u64 func##_positive_offset(u64 r3, u64 r4);
+
+DECLARE_LOAD_FUNC(sk_load_word);
+DECLARE_LOAD_FUNC(sk_load_half);
+DECLARE_LOAD_FUNC(sk_load_byte);
+
+#define CHOOSE_LOAD_FUNC(imm, func)						\
+			(imm < 0 ?						\
+			(imm >= SKF_LL_OFF ? func##_negative_offset : func) :	\
+			func##_positive_offset)
+
+#define SEEN_FUNC	0x1000 /* might call external helpers */
+#define SEEN_STACK	0x2000 /* uses BPF stack */
+#define SEEN_SKB	0x4000 /* uses sk_buff */
+
+struct codegen_context {
+	/*
+	 * This is used to track register usage as well
+	 * as calls to external helpers.
+	 * - register usage is tracked with corresponding
+	 *   bits (r3-r10 and r25-r31)
+	 * - rest of the bits can be used to track other
+	 *   things -- for now, we use bits 16 to 23
+	 *   encoded in SEEN_* macros above
+	 */
+	unsigned int seen;
+	unsigned int idx;
+};
+
+#endif /* !__ASSEMBLY__ */
+
+#endif