linux-kernel - Re: [PATCH] gcov: support GCC 7.1

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Date:   Mon, 8 May 2017 12:54:13 +0200
From:   Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Martin Liška <mliska@...e.cz>,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gcov: support GCC 7.1

I just realized (admittedly somewhat late) that this hasn't been
included yet. However this patch is still required for Linux
gcov-profiling to build with GCC 7.1.

@Andrew, could you pick this up via your tree?

The original post can be found at https://lkml.org/lkml/2016/11/24/293

On 08.12.2016 13:52, Peter Oberparleiter wrote:
> On 24.11.2016 13:46, Martin Liška wrote:
>> On 11/09/2016 10:21 AM, Peter Oberparleiter wrote:
>>> On 31.10.2016 10:35, Martin Liška wrote:
>>>> Starting from GCC 7.1, __gcov_exit is a new symbol expected
>>>> to be implemented in a profiling runtime.
>>>
>>> I tested your patch with kernel 4.9-rc4 compiled with GCC 7.0.0 20161107
>>> (experimental) and validated that it fixes the build error due to a
>>> missing __gcov_exit symbol.
>>>
>>> An attempt to read from one of the .gcda files generated by a kernel
>>> compiled this way resulted in a crash though. It appears that the number
>>> of GCOV_COUNTERS has changed again for GCC 7.x and must be adjusted in
>>> the kernel as well. Could you add that to your patch as well?
>>
>> Hello.
>>
>> Sorry, this is fixed in second version of the patch.
>>
>>> Given that GCC 7.1 has not yet been released, I'm wondering if it is
>>> safe to program against interfaces that have not yet been fully
>>> finalized. Can you provide an indication on whether these gcov-related
>>> aspects of GCC might still be changed until release?
>>
>> Well, we just flipped to stage3 which means that any new features should
>> be added to current master. If you prefer we can commit the patch after
>> a release of 7.1 will be done?
> 
> I've given this some more thought: if your patch is not applied, GCOV
> kernel profiling will definitely not work with GCC 7.x. If it is
> applied, there is a high probability that it will work, and a small
> chance that additional patches will be required. Overall I would say
> this justifies applying the patch now.
> 
>>> As a side note, please post your patches inline instead of as attachment
>>> as that helps quoting them in replies. See also
>>> linux/Documentation/SubmittingPatches.
>>
>> Sure, thanks for info. I'm attaching new version:
>>
>> Starting from GCC 7.1, __gcov_exit is a new symbol expected
>> to be implemented in a profiling runtime. Update number of profile
>> counters.
>>
>> Signed-off-by: Martin Liska <mliska@...e.cz>
> 
> Looks good, thanks! Tested successfully with GCC 7.0.0 20161208
> (experimental) on Linux kernel 4.9-rc8 (compiles successfully and
> produces valid kernel .gcda files).
> 
> Andrew, could you pick this change up via your tree?
> 
> Reviewed-by: Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
> Tested-by: Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>
> 
>> ---
>>  kernel/gcov/base.c    | 6 ++++++
>>  kernel/gcov/gcc_4_7.c | 4 +++-
>>  2 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/gcov/base.c b/kernel/gcov/base.c
>> index 2f9df37..85dca5d 100644
>> --- a/kernel/gcov/base.c
>> +++ b/kernel/gcov/base.c
>> @@ -98,6 +98,12 @@ void __gcov_merge_icall_topn(gcov_type *counters, unsigned int n_counters)
>>  }
>>  EXPORT_SYMBOL(__gcov_merge_icall_topn);
>>
>> +void __gcov_exit (void)
>> +{
>> +	/* Unused. */
>> +}
>> +EXPORT_SYMBOL(__gcov_exit);
>> +
>>  /**
>>   * gcov_enable_events - enable event reporting through gcov_event()
>>   *
>> diff --git a/kernel/gcov/gcc_4_7.c b/kernel/gcov/gcc_4_7.c
>> index 6a5c239..46a18e7 100644
>> --- a/kernel/gcov/gcc_4_7.c
>> +++ b/kernel/gcov/gcc_4_7.c
>> @@ -18,7 +18,9 @@
>>  #include <linux/vmalloc.h>
>>  #include "gcov.h"
>>
>> -#if (__GNUC__ > 5) || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)
>> +#if (__GNUC__ >= 7)
>> +#define GCOV_COUNTERS			9
>> +#elif (__GNUC__ > 5) || (__GNUC__ == 5 && __GNUC_MINOR__ >= 1)
>>  #define GCOV_COUNTERS			10
>>  #elif __GNUC__ == 4 && __GNUC_MINOR__ >= 9
>>  #define GCOV_COUNTERS			9
>>

-- 
Peter Oberparleiter
Linux on z Systems Development - IBM Germany