Re: [RFC][PATCH 0/3] Process events biarch bug: Intro

[Matt Helsley <matthltc@us.ibm.com>]

On Tue, 2006-06-27 at 16:33 +0400, Evgeniy Polyakov wrote:
> On Tue, Jun 27, 2006 at 04:47:01AM -0700, Matt Helsley (matthltc@us.ibm.com) wrote:
> > The events sent by Process Events from a 64-bit kernel are not binary compatible
> > with what a 32-bit userspace program would expect to recieve because the timespec
> > struct (used to send a timestamp) is not the same. This means that fields stored
> > after the timestamp are offset and programs that don't take this into account
> > break under these circumstances.
> > 
> > This is a problem for 32-bit userspace programs running with 64-bit kernels on
> > ppc64, s390, x86-64.. any "biarch" system.
> > 
> > This series:
> > 
> > 1 - Gives a name to the union of the process events structure so it may be used
> > 	to work around the problem from userspace.
> > 2 - Comments on the bug and describes a userspace workaround in
> > 	Documentation/connector/process_events.txt
> > 3 - Implements a second connector interface without the problem
> > 	(Removing the old interface or changing the definition would break
> > 	 binary compatibility)
> 
> If you are sure binary compatibility on this stage of process
> notification connector is really major issue, then I agree that above is
> correct, otherwise I would recommend to just replace broken code with fixed size objects.

	It's not clear whether event binary compatibility is a major issue. I
chose to assume it was and presented the best option (that I could think
of) for preserving binary compatibility.

> Btw, __u64 is not the best choice for some arches too due to it's
> alignment (64bit code requires u64 to be aligned to 64 bit, while 32bit
> code will only align it to 32 bits), so you will need 
> attribute ((aligned(8)))) for your own ___u64.

	Fixing the alignment would be a good idea. Though setting it to 8 would
introduce 4 unused bytes at the end of the structure.

Cheers,
	-Matt Helsley