Subject: Re: [PATCH V3 2/3] ARM: net: bpf_jit: make code generation less dependent on struct sk_filter.

From: Daniel Borkmann <[email-masked]>
Date: Wed, 24 Apr 2013 19:41:34 +0200

On 04/24/2013 07:27 PM, Nicolas Schichan wrote:
> This is in preparation of bpf_jit support for seccomp filters.

Please also CC the netdev list for BPF related patches.

Just to give you a heads-up, this might likely lead to a merge
conflict with the net-next tree (commit 79617801ea0c0e66, "filter:
bpf_jit_comp: refactor and unify BPF JIT image dump output").

> Signed-off-by: Nicolas Schichan <[email-masked]>
> ---
>   arch/arm/net/bpf_jit_32.c |   46 ++++++++++++++++++++++++++++-----------------
>   1 file changed, 29 insertions(+), 17 deletions(-)
>
> diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
> index a0bd8a7..bb66a2b 100644
> --- a/arch/arm/net/bpf_jit_32.c
> +++ b/arch/arm/net/bpf_jit_32.c
> @@ -55,7 +55,8 @@
>   #define FLAG_NEED_X_RESET	(1 << 0)
>
>   struct jit_ctx {
> -	const struct sk_filter *skf;
> +	unsigned short prog_len;
> +	struct sock_filter *prog_insns;
>   	unsigned idx;
>   	unsigned prologue_bytes;
>   	int ret0_fp_idx;
> @@ -131,8 +132,8 @@ static u16 saved_regs(struct jit_ctx *ctx)
>   {
>   	u16 ret = 0;
>
> -	if ((ctx->skf->len > 1) ||
> -	    (ctx->skf->insns[0].code == BPF_S_RET_A))
> +	if ((ctx->prog_len > 1) ||
> +	    (ctx->prog_insns[0].code == BPF_S_RET_A))
>   		ret |= 1 << r_A;
>
>   #ifdef CONFIG_FRAME_POINTER
> @@ -181,7 +182,7 @@ static inline bool is_load_to_a(u16 inst)
>   static void build_prologue(struct jit_ctx *ctx)
>   {
>   	u16 reg_set = saved_regs(ctx);
> -	u16 first_inst = ctx->skf->insns[0].code;
> +	u16 first_inst = ctx->prog_insns[0].code;
>   	u16 off;
>
>   #ifdef CONFIG_FRAME_POINTER
> @@ -279,7 +280,7 @@ static u16 imm_offset(u32 k, struct jit_ctx *ctx)
>   		ctx->imms[i] = k;
>
>   	/* constants go just after the epilogue */
> -	offset =  ctx->offsets[ctx->skf->len];
> +	offset =  ctx->offsets[ctx->prog_len];
>   	offset += ctx->prologue_bytes;
>   	offset += ctx->epilogue_bytes;
>   	offset += i * 4;
> @@ -419,7 +420,7 @@ static inline void emit_err_ret(u8 cond, struct jit_ctx *ctx)
>   		emit(ARM_MOV_R(ARM_R0, ARM_R0), ctx);
>   	} else {
>   		_emit(cond, ARM_MOV_I(ARM_R0, 0), ctx);
> -		_emit(cond, ARM_B(b_imm(ctx->skf->len, ctx)), ctx);
> +		_emit(cond, ARM_B(b_imm(ctx->prog_len, ctx)), ctx);
>   	}
>   }
>
> @@ -469,14 +470,13 @@ static inline void update_on_xread(struct jit_ctx *ctx)
>   static int build_body(struct jit_ctx *ctx)
>   {
>   	void *load_func[] = {jit_get_skb_b, jit_get_skb_h, jit_get_skb_w};
> -	const struct sk_filter *prog = ctx->skf;
>   	const struct sock_filter *inst;
>   	unsigned i, load_order, off, condt;
>   	int imm12;
>   	u32 k;
>
> -	for (i = 0; i < prog->len; i++) {
> -		inst = &(prog->insns[i]);
> +	for (i = 0; i < ctx->prog_len; i++) {
> +		inst = &(ctx->prog_insns[i]);
>   		/* K as an immediate value operand */
>   		k = inst->k;
>
> @@ -769,8 +769,8 @@ cmp_x:
>   				ctx->ret0_fp_idx = i;
>   			emit_mov_i(ARM_R0, k, ctx);
>   b_epilogue:
> -			if (i != ctx->skf->len - 1)
> -				emit(ARM_B(b_imm(prog->len, ctx)), ctx);
> +			if (i != ctx->prog_len - 1)
> +				emit(ARM_B(b_imm(ctx->prog_len, ctx)), ctx);
>   			break;
>   		case BPF_S_MISC_TAX:
>   			/* X = A */
> @@ -858,7 +858,7 @@ b_epilogue:
>   }
>
>
> -void bpf_jit_compile(struct sk_filter *fp)
> +static void __bpf_jit_compile(struct jit_ctx *out_ctx)
>   {
>   	struct jit_ctx ctx;
>   	unsigned tmp_idx;
> @@ -867,11 +867,10 @@ void bpf_jit_compile(struct sk_filter *fp)
>   	if (!bpf_jit_enable)
>   		return;
>
> -	memset(&ctx, 0, sizeof(ctx));
> -	ctx.skf		= fp;
> +	ctx = *out_ctx;
>   	ctx.ret0_fp_idx = -1;
>
> -	ctx.offsets = kzalloc(4 * (ctx.skf->len + 1), GFP_KERNEL);
> +	ctx.offsets = kzalloc(4 * (ctx.prog_len + 1), GFP_KERNEL);
>   	if (ctx.offsets == NULL)
>   		return;
>
> @@ -921,13 +920,26 @@ void bpf_jit_compile(struct sk_filter *fp)
>   		print_hex_dump(KERN_INFO, "BPF JIT code: ",
>   			       DUMP_PREFIX_ADDRESS, 16, 4, ctx.target,
>   			       alloc_size, false);
> -
> -	fp->bpf_func = (void *)ctx.target;
>   out:
>   	kfree(ctx.offsets);
> +
> +	*out_ctx = ctx;
>   	return;
>   }
>
> +void bpf_jit_compile(struct sk_filter *fp)
> +{
> +	struct jit_ctx ctx;
> +
> +	memset(&ctx, 0, sizeof(ctx));
> +	ctx.prog_len = fp->len;
> +	ctx.prog_insns = fp->insns;
> +
> +	__bpf_jit_compile(&ctx);
> +	if (ctx.target)
> +		fp->bpf_func = (void *)ctx.target;
> +}
> +
>   static void bpf_jit_free_worker(struct work_struct *work)
>   {
>   	module_free(NULL, work);
>