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SubjectRe: [PATCH v2] perf: Support for Arm A32/T32 instruction sets in CoreSight trace
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Hi Kim,


On 29/08/18 14:49, Kim Phillips wrote:
> On Wed, 29 Aug 2018 10:44:23 +0100
> Robert Walker <robert.walker@arm.com> wrote:
>
>> This patch adds support for generating instruction samples from trace of
>> AArch32 programs using the A32 and T32 instruction sets.
>>
>> T32 has variable 2 or 4 byte instruction size, so the conversion between
>> addresses and instruction counts requires extra information from the trace
>> decoder, requiring version 0.9.1 of OpenCSD. A check for the new struct
>> member has been added to the feature check for OpenCSD.
>>
>> Signed-off-by: Robert Walker <robert.walker@arm.com>
>> ---
> ...
>> +++ b/tools/build/feature/test-libopencsd.c
>> @@ -3,6 +3,13 @@
>>
>> int main(void)
>> {
>> + /*
>> + * Requires ocsd_generic_trace_elem.num_instr_range introduced in
>> + * OpenCSD 0.9
> 0.9 != 0.9.1 in the above commit text: which is it?
I'll change it to 0.9.1 if there's another version of the patch (it was
introduced in 0.9, but 0.9.1 has a necessary bug fix)
>> + */
>> + ocsd_generic_trace_elem elem;
>> + (void)elem.num_instr_range;
>> +
> This breaks building against older versions of OpenCSD, right?
>
>> (void)ocsd_get_version();
> Why don't we maintain building against older versions of the library,
> and use the version information to make the decision on whether to use
> the new feature being introduced in this patch?
The intention is to fail the feature detection check if the older
version is installed - perf will still compile, but without the
CoreSight trace support.

OpenCSD is still in development, so new features like this are being
added and it would add a lot of #ifdef mess to the perf code to continue
to support any machines with the old library version installed - there
will only be a handful of machines affected and it's trivial to upgrade
them (the new Debian packages are available).  How long would we
continue to support such an older version?  I also don't see any
precedent for supporting multiple dependent library versions in perf.
>
> Thanks,
>
> Kim
Regards

Rob

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