[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20150211093308.GN23123@twins.programming.kicks-ass.net>
Date: Wed, 11 Feb 2015 10:33:08 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Alexei Starovoitov <ast@...mgrid.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Arnaldo Carvalho de Melo <acme@...radead.org>,
Jiri Olsa <jolsa@...hat.com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Linux API <linux-api@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v3 linux-trace 1/8] tracing: attach eBPF programs to
tracepoints and syscalls
On Tue, Feb 10, 2015 at 04:22:50PM -0800, Alexei Starovoitov wrote:
> >> not all tools use libtraceevent.
> >> gdb calls perf_event_open directly:
> >> https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=gdb/nat/linux-btrace.c
> >> and parses PERF_RECORD_SAMPLE as a binary.
> >> In this case it's branch records, but I think we never said anywhere
> >> that PERF_SAMPLE_IP | PERF_SAMPLE_ADDR should come
> >> in this particular order.
> >
> > What particular order? Note, that's a hardware event, not a software
> > one.
>
> yes, but gdb assumes that 'u64 ip' precedes, 'u64 addr'
> when attr.sample_type = IP | ADDR whereas this is an
> internal order of 'if' statements inside perf_output_sample()...
This is indeed promised in the data layout description in
include/uapi/linux/perf_event.h.
There is no other way to find where fields are; perf relies on
predetermined order of fields coupled with the requested field bitmask.
So we promise the order: id, ip, pid, tid, time, addr,.. etc.
So if you request IP and ADDR but none of the other fields, then you
know your sample will start with IP and then contain ADDR.
The traceevent thing has a debug/trace-fs format description of fields
that is supposed to be used.
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Powered by blists - more mailing lists