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Date: Fri, 15 Aug 2014 12:02:51 -0700 From: Andy Lutomirski <luto@...capital.net> To: Alexei Starovoitov <ast@...mgrid.com> Cc: Daniel Borkmann <dborkman@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>, Linux API <linux-api@...r.kernel.org>, Chema Gonzalez <chema@...gle.com>, Eric Dumazet <edumazet@...gle.com>, "David S. Miller" <davem@...emloft.net>, Brendan Gregg <brendan.d.gregg@...il.com>, Linus Torvalds <torvalds@...ux-foundation.org>, Steven Rostedt <rostedt@...dmis.org>, LKML <linux-kernel@...r.kernel.org>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Kees Cook <keescook@...omium.org>, Network Development <netdev@...r.kernel.org>, Ingo Molnar <mingo@...nel.org> Subject: Re: [PATCH RFC v4 net-next 17/26] tracing: allow eBPF programs to be attached to events On Fri, Aug 15, 2014 at 11:56 AM, Alexei Starovoitov <ast@...mgrid.com> wrote: > On Fri, Aug 15, 2014 at 11:50 AM, Andy Lutomirski <luto@...capital.net> wrote: >> On Aug 15, 2014 10:36 AM, "Alexei Starovoitov" <ast@...mgrid.com> wrote: >>> >>> On Fri, Aug 15, 2014 at 10:20 AM, Andy Lutomirski <luto@...capital.net> wrote: >>> > The downside of this approach is that compat support might be >>> > difficult or impossible. >>> >>> Would do you mean by compat? 32-bit programs on 64-bit kernels? >>> There is no such concept for eBPF. All eBPF programs are always >>> operating on 64-bit registers. >> >> Doesn't the eBPF program need to know sizeof(long) to read these >> fields correctly? Or am I misunderstanding what the code does? > > correct. eBPF program would be using 8-byte read on 64-bit kernel > and 4-byte read on 32-bit kernel. Same with access to ptrace fields > and pretty much all other fields in the kernel. The program will be > different on different kernels. > Say, this bpf_context struct doesn't exist at all. The programs would > still need to be different to walk in-kernel data structures... Hmm. I guess this isn't so bad. What's the actual difficulty with using u64? ISTM that, if the clang front-end can't deal with u64, there's a bigger problem. Or is it something else I don't understand. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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