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To: Ingo Molnar <mingo@elte.hu>
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From: fche@redhat.com (Frank Ch. Eigler)
Date: Mon, 07 Nov 2011 15:03:00 -0500
In-Reply-To: <20111107175942.GA9395@elte.hu> (Ingo Molnar's message of "Mon, 7 Nov 2011 18:59:42 +0100")
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Ingo Molnar <mingo@elte.hu> writes:

> [...]
>> It's problem enough that there's no way to know what version of the 
>> perf_event abi you are running against and we have to guess based 
>> on kernel version.  This gets "fun" because all of the vendors have 
>> backported seemingly random chunks of perf_event code to their 
>> older kernels.
>
> The ABI design allows for that kind of flexible extensibility, and 
> it's one of its major advantages.
>
> What we *cannot* protect against is you relying on obscure details of 
> the ABI [...]

Is there some documentation that clearly spells out which parts of the
perf syscall userspace ABI are "obscure" and thus presumably
changeable?

> [...]  The usual ABI rules also apply: we'll revert everything that
> breaks the ABI - but for that you need to report it *in time* [...]

If the ABI is so great in its flexible extensibility, how come it
can't be flexibly extended without having to passing the burden of
compatibility testing & reversion-yawping to someone else?


- FChE