linux-kernel - Re: [PATCH] perfcounters: fix type/event

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 21 Mar 2009 10:56:52 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] perfcounters: fix type/event_id layout on big-endian
	systems


* Paul Mackerras <paulus@...ba.org> wrote:

> Ingo Molnar writes:
> 
> > hm, this ifdef really looks ugly. How about just changing event_id 
> > to 64 bits and having a separate u32 type field? The size impact is 
> > minimal, the cleanliness win is significant :-)
> 
> We wanted to get a complete and unique identifier for the event 
> into 64 bits so that we could put it into the ring buffer for 
> PERF_RECORD_GROUP and have it take up only one 8-byte slot and yet 
> identify uniquely which counter's value follows it.  I don't know 
> that that is absolutely necessary but it sounds like a nice 
> property.
> 
> We could easily go back to a 1-bit raw field and have the type be 
> either a 64-bit raw value or an 8-bit type plus 32 or 56-bit 
> event_id.
> 
> Or we could keep the current layout but use explicit shifts and 
> masks rather than bitfields.
> 
> I don't know the current C rules concerning unions very well, but 
> I have the impression that writing to one member of a union and 
> reading another is undefined behaviour, which is another strike 
> against the current code if true...
>
> Anyway, the point is that the current code doesn't compile on 
> powerpc and wouldn't work properly even if it did, so we need to 
> do something.

yeah - i pulled your fix, thanks Paul.

Maybe the best option is to get rid of the bitfields and use masks 
...

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/