From: Steven Rostedt <rostedt@goodmis.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
linux-kernel@vger.kernel.org,
Linus Torvalds <torvalds@linux-foundation.org>,
Ingo Molnar <mingo@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Masami Hiramatsu <mhiramat@kernel.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Matthew Helsley <mhelsley@vmware.com>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
David Woodhouse <dwmw2@infradead.org>,
Paolo Bonzini <pbonzini@redhat.com>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Jason Baron <jbaron@akamai.com>, Jiri Kosina <jkosina@suse.cz>,
ard.biesheuvel@linaro.org, Andy Lutomirski <luto@kernel.org>
Subject: Re: [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function"
Date: Mon, 8 Oct 2018 12:31:40 -0400 [thread overview]
Message-ID: <20181008123140.666fa405@gandalf.local.home> (raw)
In-Reply-To: <20181008155757.GC5663@hirez.programming.kicks-ass.net>
On Mon, 8 Oct 2018 17:57:57 +0200
Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Oct 08, 2018 at 01:33:14AM -0700, Andy Lutomirski wrote:
> > > Can't we hijack the relocation records for these functions before they
> > > get thrown out in the (final) link pass or something?
> >
> > I could be talking out my arse here, but I thought we could do this,
> > too, then changed my mind. The relocation records give us the
> > location of the call or jump operand, but they don’t give the address
> > of the beginning of the instruction.
>
> But that's like 1 byte before the operand, right? We could even double check
> this by reading back that byte and ensuring it is in fact 0xE8 (CALL).
>
> AFAICT there is only the _1_ CALL encoding, and that is the 5 byte: E8 <PLT32>,
> so if we have the PLT32 location, we also have the instruction location. Or am
> I missing something?
Yes, this is exactly what I was thinking of doing. All we need to do is
have objtool (or a modification of whatever we come up with), to find
the call sites of a specific function (we can have a table to look up
for), that creates a section listing all these call sites, and on boot
up, we can confirm that they are indeed calls (e8 operations).
-- Steve
next prev parent reply other threads:[~2018-10-08 16:31 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-06 1:51 [POC][RFC][PATCH 0/2] PROOF OF CONCEPT: Dynamic Functions (jump functions) Steven Rostedt
2018-10-06 1:51 ` [POC][RFC][PATCH 1/2] jump_function: Addition of new feature "jump_function" Steven Rostedt
2018-10-06 2:00 ` Steven Rostedt
2018-10-06 2:02 ` Steven Rostedt
2018-10-06 2:03 ` Steven Rostedt
2018-10-06 15:15 ` Steven Rostedt
2018-10-06 12:12 ` Peter Zijlstra
2018-10-06 13:39 ` Steven Rostedt
2018-10-06 15:13 ` Andy Lutomirski
2018-10-06 15:16 ` Steven Rostedt
2018-10-08 7:21 ` Peter Zijlstra
2018-10-08 8:33 ` Andy Lutomirski
2018-10-08 15:57 ` Peter Zijlstra
2018-10-08 16:29 ` Andy Lutomirski
2018-10-08 16:39 ` Steven Rostedt
2018-10-08 16:39 ` Peter Zijlstra
2018-10-08 17:25 ` Andy Lutomirski
2018-10-08 17:30 ` Ard Biesheuvel
2018-10-08 17:42 ` Andy Lutomirski
2018-10-08 17:44 ` Jiri Kosina
2018-10-08 17:45 ` Ard Biesheuvel
2018-10-08 17:47 ` Andy Lutomirski
2018-10-09 2:17 ` Josh Poimboeuf
2018-10-09 3:57 ` Steven Rostedt
2018-10-10 17:52 ` Josh Poimboeuf
2018-10-10 18:03 ` Andy Lutomirski
2018-10-10 18:16 ` Josh Poimboeuf
2018-10-10 18:17 ` Josh Poimboeuf
2018-10-10 21:13 ` Andy Lutomirski
2018-10-11 3:07 ` Josh Poimboeuf
2018-10-11 12:52 ` Josh Poimboeuf
2018-10-11 16:20 ` Andy Lutomirski
2018-10-10 18:33 ` Josh Poimboeuf
2018-10-10 18:56 ` Steven Rostedt
2018-10-10 20:16 ` Josh Poimboeuf
2018-10-10 20:57 ` Andy Lutomirski
2018-10-08 16:31 ` Steven Rostedt [this message]
2018-10-08 11:30 ` Ard Biesheuvel
2018-10-09 3:44 ` Masami Hiramatsu
2018-10-09 3:55 ` Steven Rostedt
2018-10-09 16:04 ` Masami Hiramatsu
2018-10-09 8:59 ` David Laight
2018-10-06 1:51 ` [POC][RFC][PATCH 2/2] tracepoints: Implement it with dynamic functions Steven Rostedt
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