linux-kernel - Re: [PATCH, REPORT] bpf_trace: build error without PERF

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Message-ID: <56422802.5050901@iogearbox.net>
Date:	Tue, 10 Nov 2015 18:23:14 +0100
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <alexei.starovoitov@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>
CC:	Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...hat.com>,
	linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Kaixu Xia <xiakaixu@...wei.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Wang Nan <wangnan0@...wei.com>, netdev@...r.kernel.org,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH, REPORT] bpf_trace: build error without PERF_EVENTS

On 11/10/2015 06:14 PM, Alexei Starovoitov wrote:
> On Tue, Nov 10, 2015 at 09:25:01AM -0500, Steven Rostedt wrote:
>> On Tue, 10 Nov 2015 14:31:38 +0100
>> Daniel Borkmann <daniel@...earbox.net> wrote:
>>
>>> On 11/10/2015 01:55 PM, Arnd Bergmann wrote:
>>>> In my ARM randconfig tests, I'm getting a build error for
>>>> newly added code in bpf_perf_event_read and bpf_perf_event_output
>>>> whenever CONFIG_PERF_EVENTS is disabled:
>>>>
>>>> kernel/trace/bpf_trace.c: In function 'bpf_perf_event_read':
>>>> kernel/trace/bpf_trace.c:203:11: error: 'struct perf_event' has no member named 'oncpu'
>>>> if (event->oncpu != smp_processor_id() ||
>>>>            ^
>>>> kernel/trace/bpf_trace.c:204:11: error: 'struct perf_event' has no member named 'pmu'
>>>>         event->pmu->count)
>>>>
>>>> This can happen when UPROBE_EVENT is enabled but KPROBE_EVENT
>>>> is disabled. I'm not sure if that is a configuration we care
>>>> about, otherwise we could prevent this case from occuring by
>>>> adding Kconfig dependencies.
>>>
>>> I think that seems better than spreading #if IS_ENABLEDs into the code.
>>> Probably enough to add a 'depends on PERF_EVENTS' to config BPF_EVENTS,
>>> so it's also explicitly documented.
>>>
>>
>> So just do the following then?
>>
>> -- Steve
>>
>> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
>> index 8d6363f42169..f5aecff2d243 100644
>> --- a/kernel/trace/Kconfig
>> +++ b/kernel/trace/Kconfig
>> @@ -434,7 +434,7 @@ config UPROBE_EVENT
>>
>>   config BPF_EVENTS
>>   	depends on BPF_SYSCALL
>> -	depends on KPROBE_EVENT || UPROBE_EVENT
>> +	depends on KPROBE_EVENT && UPROBE_EVENT
>
> yeah that's definitely cleaner and avoids ifdef creep in the future.

Agreed, that's better.
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