linux-kernel - Re: [PATCH] jprobes: Ensure that the probepoint is at function entry

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Message-ID: <20170706121549.iqwcqh6xg4cyli5p@gmail.com>
Date:   Thu, 6 Jul 2017 14:15:49 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>,
        Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jprobes: Ensure that the probepoint is at function entry

* Masami Hiramatsu <mhiramat@...nel.org> wrote:

> > Also, 'function_offset_within_entry' is way too long a name, and it's also a 
> > minomer I think. The purpose of this function is to enforce that the relative 
> > 'offset' of a new probe is at the standard function entry offset: i.e. 0 on most 
> > architectures, and some ABI dependent constant on PowerPC, right?
> > 
> > That's not at all clear from that name, plus it's a global namespace symbol, yet 
> > has no 'kprobes' prefix. So it should be named something like 
> > 'kprobe_offset_valid()' or such, with an arch_kprobe_offset_valid() counterpart.
> 
> Hmm, I would rather like kprobe_within_entry(), since offset != 0 is
> actually valid for normal kprobe, that is kretprobe and jprobe limitation.

But what entry? That it's within a range or that offset is always 0 is really an 
implementational detail: depending on what type of kprobe it is, it is either 
validly within the confines of the specified function symbol or not.

What _really_ matters to callers is whether it's a valid kprobe to be inserted 
into that function, right?

I.e. the long name came from over-specifying what is done by the function - while 
simplifying makes it actually more meaningful to read.

Thanks,

	Ingo