netdev - Re: [PATCH 2/2] sparc64: Add eBPF JIT.

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Message-ID: <20170422153233.GA47144@ast-mbp.thefacebook.com>
Date:   Sat, 22 Apr 2017 08:32:35 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     sparclinux@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH 2/2] sparc64: Add eBPF JIT.

On Fri, Apr 21, 2017 at 08:17:11PM -0700, David Miller wrote:
> 
> This is an eBPF JIT for sparc64.  All major features are supported.
> 
> All tests under tools/testing/selftests/bpf/ pass.
> 
> Signed-off-by: David S. Miller <davem@...emloft.net>
...
> +	/* tail call */
> +	case BPF_JMP | BPF_CALL |BPF_X:
> +		emit_tail_call(ctx);
> +

I think 'break;' is missing here.
When tail_call's target program is null the current program should
continue instead of aborting.
Like in our current ddos+lb setup the program looks like:
 bpf_tail_call(ctx, &prog_array, 1);
 bpf_tail_call(ctx, &prog_array, 2);
 bpf_tail_call(ctx, &prog_array, 3);
 return XDP_DROP;

this way it will jump into the program that is installed in slot 1.
If it's empty, it will try slot 2...
If no programs installed it will drop the packet.

> +	/* function return */
> +	case BPF_JMP | BPF_EXIT:
> +		/* Optimization: when last instruction is EXIT,
> +		   simply fallthrough to epilogue. */
> +		if (i == ctx->prog->len - 1)
> +			break;
> +		emit_branch(BA, ctx->idx, ctx->epilogue_offset, ctx);
> +		emit_nop(ctx);