linux-kernel - [RFC] perf: perf_event_attr anon unions and static initializer issue

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Message-ID: <CABPqkBRCjd5=9t1URNXQvu8GbAHMjf3ixKtb6BV7ebBTZDLF1A@mail.gmail.com>
Date:	Fri, 5 Oct 2012 12:36:04 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>, David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Namhyung Kim <namhyung.kim@....com>
Subject: [RFC] perf: perf_event_attr anon unions and static initializer issue

Hi,

I am writing a little test program for the perf_event API which is using
hardcoded events. Some of those events (SNBEP uncore events) require
a value for config1. I was naively assuming, one could simply do:

struct perf_event_attr attr = { .config = 0x1234, .config1 = 0x456 };

However this does not work with gcc version < 4.6 apparently. Don't
know how this even works with other compilers. I looked online and
I could not really find a good way of solving this that would be portable
across compiler versions.

If we name those unions, then this will break lots of existing programs.
We'd have to create a "named" version of perf_event_attr and then
memcpy() at runtime. Or simply initialize the .config1 and such fields at
runtime from a separate table.

Does anyone have a better solution to propose?
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