path: root/arch/mips/net/bpf_jit.c

/*
 * Just-In-Time compiler for BPF filters on MIPS
 *
 * Copyright (c) 2014 Imagination Technologies Ltd.
 * Author: Markos Chandras <markos.chandras@imgtec.com>
 *
 * 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.
 */

#include <linux/bitops.h>
#include <linux/compiler.h>
#include <linux/errno.h>
#include <linux/filter.h>
#include <linux/if_vlan.h>
#include <linux/moduleloader.h>
#include <linux/netdevice.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <asm/asm.h>
#include <asm/bitops.h>
#include <asm/cacheflush.h>
#include <asm/cpu-features.h>
#include <asm/uasm.h>

#include "bpf_jit.h"

/* ABI
 * r_skb_hl	SKB header length
 * r_data	SKB data pointer
 * r_off	Offset
 * r_A		BPF register A
 * r_X		BPF register X
 * r_skb	*skb
 * r_M		*scratch memory
 * r_skb_len	SKB length
 *
 * On entry (*bpf_func)(*skb, *filter)
 * a0 = MIPS_R_A0 = skb;
 * a1 = MIPS_R_A1 = filter;
 *
 * Stack
 * ...
 * M[15]
 * M[14]
 * M[13]
 * ...
 * M[0] <-- r_M
 * saved reg k-1
 * saved reg k-2
 * ...
 * saved reg 0 <-- r_sp
 * <no argument area>
 *
 *                     Packet layout
 *
 * <--------------------- len ------------------------>
 * <--skb-len(r_skb_hl)-->< ----- skb->data_len ------>
 * ----------------------------------------------------
 * |                  skb->data                       |
 * ----------------------------------------------------
 */

#define ptr typeof(unsigned long)

#define SCRATCH_OFF(k)		(4 * (k))

/* JIT flags */
#define SEEN_CALL		(1 << BPF_MEMWORDS)
#define SEEN_SREG_SFT		(BPF_MEMWORDS + 1)
#define SEEN_SREG_BASE		(1 << SEEN_SREG_SFT)
#define SEEN_SREG(x)		(SEEN_SREG_BASE << (x))
#define SEEN_OFF		SEEN_SREG(2)
#define SEEN_A			SEEN_SREG(3)
#define SEEN_X			SEEN_SREG(4)
#define SEEN_SKB		SEEN_SREG(5)
#define SEEN_MEM		SEEN_SREG(6)
/* SEEN_SK_DATA also implies skb_hl an skb_len */
#define SEEN_SKB_DATA		(SEEN_SREG(7) | SEEN_SREG(1) | SEEN_SREG(0))

/* Arguments used by JIT */
#define ARGS_USED_BY_JIT	2 /* only applicable to 64-bit */

#define SBIT(x)			(1 << (x)) /* Signed version of BIT() */

/**
 * struct jit_ctx - JIT context
 * @skf:		The sk_filter
 * @prologue_bytes:	Number of bytes for prologue
 * @idx:		Instruction index
 * @flags:		JIT flags
 * @offsets:		Instruction offsets
 * @target:		Memory location for the compiled filter
 */
struct jit_ctx {
	const struct bpf_prog *skf;
	unsigned int prologue_bytes;
	u32 idx;
	u32 flags;
	u32 *offsets;
	u32 *target;
};


static inline int optimize_div(u32 *k)
{
	/* power of 2 divides can be implemented with right shift */
	if (!(*k & (*k-1))) {
		*k = ilog2(*k);
		return 1;
	}

	return 0;
}

static inline void emit_jit_reg_move(ptr dst, ptr src, struct jit_ctx *ctx);

/* Simply emit the instruction if the JIT memory space has been allocated */
#define emit_instr(ctx, func, ...)			\
do {							\
	if ((ctx)->target != NULL) {			\
		u32 *p = &(ctx)->target[ctx->idx];	\
		uasm_i_##func(&p, ##__VA_ARGS__);	\
	}						\
	(ctx)->idx++;					\
} while (0)

/*
 * Similar to emit_instr but it must be used when we need to emit
 * 32-bit or 64-bit instructions
 */
#define emit_long_instr(ctx, func, ...)			\
do {							\
	if ((ctx)->target != NULL) {			\
		u32 *p = &(ctx)->target[ctx->idx];	\
		UASM_i_##func(&p, ##__VA_ARGS__);	\
	}						\
	(ctx)->idx++;					\
} while (0)

/* Determine if immediate is within the 16-bit signed range */
static inline bool is_range16(s32 imm)
{
	return !(imm >= SBIT(15) || imm < -SBIT(15));
}

static inline void emit_addu(unsigned int dst, unsigned int src1,
			     unsigned int src2, struct jit_ctx *ctx)
{
	emit_instr(ctx, addu, dst, src1, src2);
}

static inline void emit_nop(struct jit_ctx *ctx)
{
	emit_instr(ctx, nop);
}

/* Load a u32 immediate to a register */
static inline void emit_load_imm(unsigned int dst, u32 imm, struct jit_ctx *ctx)
{
	if (ctx->target != NULL) {
		/* addiu can only handle s16 */
		if (!is_range16(imm)) {
			u32 *p = &ctx->target[ctx