Re: [PATCH v6 00/14] uprobes: Add uprobes support for ARM

[David Long <dave.long@linaro.org>]

On 03/04/14 12:31, Oleg Nesterov wrote:
> On 03/04, Russell King - ARM Linux wrote:
>>
>> On Mon, Mar 03, 2014 at 09:50:39PM +0100, Oleg Nesterov wrote:
>>>
>>> And why CONFIG_UPROBES should depend on PERF_EVENTS? uprobes can be
>>> used by (say) systemtap without UPROBE_EVENT/PERF_EVENTS.
>>>
>>> But as Russell pointed out the events directory is only built if
>>> CONFIG_PERF_EVENTS=y, so it should depend on it or select...
>>>
>>>
>>> I dunno. Personally I vote for the patch from Srikar in
>>>
>>> 	http://article.gmane.org/gmane.linux.kernel/1017186
>>>
>>> This is what we currently have, currently CONFIG_UPROBES is not
>>> user-selectable anyway.
>>
>> Yes, me too, but with the proviso that UPROBE_EVENT also sorts itself
>> out with PERF_EVENTS in some way too (either by selecting it, which
>> IMHO isn't nice, or by depending on it, or the build dependency itself
>> gets sorted.)
>
> OK... what do you think about the patch below for now?
>
>> Maybe a simpler answer would be to change the build stuff (hand-crafted):
>>
>> kernel/Makefile
>> -obj-$(CONFIG_PERF_EVENTS) += events/
>> +obj-y += events/
>>
>> and kernel/events/Makefile:
>>
>> -obj-y := core.o ring_buffer.o callchain.o
>> +perf-y := core.o ring_buffer.o callchain.o
>>
>> -obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
>> +perf-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
>> +
>> +obj-${CONFIG_PERF_EVENTS) += $(perf-y)
>
> I fully agree. Except I can't review this change ;) But hopefully I
> can understand what it should do.
>
> But personally I'd prefer to start with the simple/safe change which
> allows us to merge this series. If nothing else, even if I think that
> kernel/events/uprobes.c doesn't need CONFIG_PERF_EVENTS, this should
> be verified and discussed with perf maintainers.
>
> If you agree with the patch below, how should we route it? I won't
> argue if you push it along with other patches from David.
>

Oleg, I'll put you down as the author and add a signed-off line for you 
if that is OK?  Not sure who should ack it.

> BTW... why UPROBE_EVENT depends on MMU? I think that ARCH_SUPPORTS_UPROBES
> should not be true if !CONFIG_MMU.
>
> Oleg.
> ---
>
> diff --git a/arch/Kconfig b/arch/Kconfig
> index 80bbb8c..97ff872 100644
> --- a/arch/Kconfig
> +++ b/arch/Kconfig
> @@ -86,9 +86,7 @@ config KPROBES_ON_FTRACE
>   	 optimize on top of function tracing.
>
>   config UPROBES
> -	bool "Transparent user-space probes (EXPERIMENTAL)"
> -	depends on UPROBE_EVENT && PERF_EVENTS
> -	default n
> +	def_bool n
>   	select PERCPU_RWSEM
>   	help
>   	  Uprobes is the user-space counterpart to kprobes: they
> @@ -101,8 +99,6 @@ config UPROBES
>   	    managed by the kernel and kept transparent to the probed
>   	    application. )
>
> -	  If in doubt, say "N".
> -
>   config HAVE_64BIT_ALIGNED_ACCESS
>   	def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
>   	help
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 015f85a..8639819 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -424,6 +424,7 @@ config UPROBE_EVENT
>   	bool "Enable uprobes-based dynamic events"
>   	depends on ARCH_SUPPORTS_UPROBES
>   	depends on MMU
> +	depends on PERF_EVENTS
>   	select UPROBES
>   	select PROBE_EVENTS
>   	select TRACING
>

Can we agree Oleg's patch above is the best way to go in the short term? 
  I've tested it and it addresses the problem, although of course one 
has to know to enable PERF_EVENTS to even see the UPROBE_EVENT option 
(not a problem on x86 as they always set PERF_EVENTS).

I'm continuing to test the above with my new include file changes, using 
Arnd's randconfig patches.  Looks good so far.

-dl