When return from exception, we need to distinguish if it's system call
return or for other type exceptions for setting sample flags.  Due to
the exception return packet doesn't contain exception number, so we
cannot decide sample flags based on exception number.

On the other hand, the exception return packet is followed by an
instruction range packet; this range packet deliveries the start address
after exception handling, we can check if it is a SVC instruction just
before the start address.  If there has one SVC instruction is found
ahead the return address, this means it's an exception return for system
call; otherwise it is an normal return for other exceptions.

This patch is to set sample flags for exception return packet, firstly
it simply set sample flags as PERF_IP_FLAG_INTERRUPT for all exception
returns since at this point it doesn't know what's exactly the exception
type.  We will defer to decide if it's an exception return for system
call when the next instruction range packet comes, it checks if there
has one SVC instruction prior to the start address and if so we will
change sample flags to PERF_IP_FLAG_SYSCALLRET for system call return.
Signed-off-by: NLeo Yan <leo.yan@linaro.org>
Reviewed-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Robert Walker <robert.walker@arm.com>
Cc: Suzuki K Poulouse <suzuki.poulose@arm.com>
Cc: coresight ml <coresight@lists.linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/20190129122842.32041-9-leo.yan@linaro.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>