Re: [PATCH] configure: check for perf_event.h version

[Pedro Alves <palves@redhat.com>]

On 08/06/2015 04:00 PM, Metzger, Markus T wrote:
>> -----Original Message-----
>> From: Pedro Alves [mailto:palves@redhat.com]
>> Sent: Thursday, August 6, 2015 4:29 PM
>> To: Metzger, Markus T
>> Cc: gdb-patches@sourceware.org
>> Subject: Re: [PATCH] configure: check for perf_event.h version
>>
>> On 08/06/2015 03:14 PM, Metzger, Markus T wrote:
>>>> -----Original Message-----
>>>> From: Pedro Alves [mailto:palves@redhat.com]
>>>> Sent: Thursday, August 6, 2015 3:49 PM
>>>> To: Metzger, Markus T
>>>> Cc: gdb-patches@sourceware.org
>>>> Subject: Re: [PATCH] configure: check for perf_event.h version
>>>>
>>>> On 08/06/2015 02:06 PM, Markus Metzger wrote:
>>>>> Intel(R) Processor Trace support requires a recent linux/perf_event.h
>>>> header.
>>>>>
>>>>> When GDB is built on an older system, Intel(R) Processor Trace will not
>> be
>>>>> available and there is no indication in the configure and build log as to
>>>>> what went wrong.
>>>>>
>>>>> Check for a compatible linux/perf_event.h at configure-time.
>>>>
>>>>
>>>>> diff --git a/gdb/configure.ac b/gdb/configure.ac
>>>>> index 905c27b..d867e85 100644
>>>>> --- a/gdb/configure.ac
>>>>> +++ b/gdb/configure.ac
>>>>> @@ -1252,6 +1252,20 @@ if test "${with_intel_pt}" = no; then
>>>>>    AC_MSG_WARN([Intel(R) Processor Trace support disabled; some
>>>> features may be unavailable.])
>>>>>    HAVE_LIBIPT=no
>>>>>  else
>>>>> +  AC_PREPROC_IFELSE(AC_LANG_SOURCE([[
>>>>> +#include <linux/perf_event.h>
>>>>> +#ifdef PERF_ATTR_SIZE_VER5
>>>>> +# error
>>>>> +#endif
>>>>
>>>> Can you explain what kind of symbol PERF_ATTR_SIZE_VER5 is?
>>>> From the patch, I understand that that is something that is _not_
>>>> defined in the perf versions that are supposedly supported?
>>>> (otherwise, I'd expect an #ifndef instead.)
>>>
>>> It's a macro.
>>
>> Was there ever a  PERF_ATTR_SIZE_VER4 symbol?   What if
>> PERF_ATTR_SIZE_VER6 is ever created?  Do we want to have to
>> check for it explicitly then?
> 
> The linux/perf_event.h header defines the macros for all previous
> versions.  The current version thus defines
> 
> #define PERF_ATTR_SIZE_VER0     64      /* sizeof first published struct */
> #define PERF_ATTR_SIZE_VER1     72      /* add: config2 */
> #define PERF_ATTR_SIZE_VER2     80      /* add: branch_sample_type */
> #define PERF_ATTR_SIZE_VER3     96      /* add: sample_regs_user */
>                                         /* add: sample_stack_user */
> #define PERF_ATTR_SIZE_VER4     104     /* add: sample_regs_intr */
> #define PERF_ATTR_SIZE_VER5     112     /* add: aux_watermark */

Ah.  Thanks.

Thanks,
Pedro Alves