linux-kernel - Re: [PATCH v2 net] bpf: x86: fix epilogue generation for eBPF programs

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Date:	Fri, 05 Dec 2014 21:24:33 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	zlim.lnx@...il.com, edumazet@...gle.com, dborkman@...hat.com,
	hpa@...or.com, tglx@...utronix.de, mingo@...nel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net] bpf: x86: fix epilogue generation for eBPF
 programs

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Sat, 29 Nov 2014 14:46:13 -0800

> classic BPF has a restriction that last insn is always BPF_RET.
> eBPF doesn't have BPF_RET instruction and this restriction.
> It has BPF_EXIT insn which can appear anywhere in the program
> one or more times and it doesn't have to be last insn.
> Fix eBPF JIT to emit epilogue when first BPF_EXIT is seen
> and all other BPF_EXIT instructions will be emitted as jump.
> 
> Since jump offset to epilogue is computed as:
> jmp_offset = ctx->cleanup_addr - addrs[i]
> we need to change type of cleanup_addr to signed to compute the offset as:
> (long long) ((int)20 - (int)30)
> instead of:
> (long long) ((unsigned int)20 - (int)30)
> 
> Fixes: 622582786c9e ("net: filter: x86: internal BPF JIT")
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

Applied, thanks.
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