From mboxrd@z Thu Jan  1 00:00:00 1970
From: Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [PATCH RFC v4 net-next 01/26] net: filter: add "load 64-bit immediate"
 eBPF instruction
Date: Wed, 13 Aug 2014 19:39:56 +0200
Message-ID: <53EBA2EC.3030306@redhat.com>
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Cc: "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Linus Torvalds <torvalds-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
	Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>,
	Chema Gonzalez <chema-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Eric Dumazet <edumazet-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>,
	"H. Peter Anvin" <hpa-YMNOUZJC4hwAvxtiuMwx3w@public.gmane.org>,
	Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	Linux API <linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	Network Development <netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	LKML <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
To: Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
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On 08/13/2014 07:34 PM, Alexei Starovoitov wrote:
> On Wed, Aug 13, 2014 at 2:17 AM, Daniel Borkmann <dborkman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>> On 08/13/2014 09:57 AM, Alexei Starovoitov wrote:
>>>
>>> add BPF_LD_IMM64 instruction to load 64-bit immediate value into register.
>>> All previous instructions were 8-byte. This is first 16-byte instruction.
>>> Two consecutive 'struct bpf_insn' blocks are interpreted as single
>>> instruction:
>>> insn[0/1].code = BPF_LD | BPF_DW | BPF_IMM
>>> insn[0/1].dst_reg = destination register
>>> insn[0].imm = lower 32-bit
>>> insn[1].imm = upper 32-bit
>>>
>>> Classic BPF has similar instruction: BPF_LD | BPF_W | BPF_IMM
>>> which loads 32-bit immediate value into a register.
>>>
>>> x64 JITs it as single 'movabsq %rax, imm64'
>>> arm64 may JIT as sequence of four 'movk x0, #imm16, lsl #shift' insn
>>>
>>> Note that old eBPF programs are binary compatible with new interpreter.
>>>
>>> Signed-off-by: Alexei Starovoitov <ast-uqk4Ao+rVK5Wk0Htik3J/w@public.gmane.org>
>>
>>
>> For follow-ups on this series, can you put the actual motivation
>> for this change from the cover letter into this commit log as it
>> otherwise doesn't say anything clearly why it is needed. Code and
>> test case looks good to me.
>
> ok. As you saw the full explanation is long, so I opted for 'it_does_this'
> commit log. In the next rev will add more reasons to this log. Sure.

Great, thanks.