linux-kernel - Re: [RFC] perf record: missing buildid for callstack modules

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Message-ID: <20160112130815.77c1a4fa@lxorguk.ukuu.org.uk>
Date:	Tue, 12 Jan 2016 13:08:15 +0000
From:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Stephane Eranian <eranian@...gle.com>,
	Namhyung Kim <namhyung@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Jiri Olsa <jolsa@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>
Subject: Re: [RFC] perf record: missing buildid for callstack modules

> And we cannot, at mmap() time, 'assume' the file is ELF and try prodding
> into it to find a buildid or whatnot.

And you cannot at any time assume that something like NFS won't change
the page contents under you. In fact it's valid (but completely insane)
to use MAP_DISCARD to throw away part of your program and page it back in
again so that a daemon on the other side of the NFS can change the code
you are executing 8)

Alan