Hi,
A new branch of OpenCSD is available - ocsd-consistency-checks-1.5.4-rc1
Testing I managed to do confirms the N atom on unconditional branches appear to work. I do not have a test case for the range discontinuities.
The checks are enabled using operation flags on decoder creation. See the docs for details.
Mike
On Fri, 9 Aug 2024 at 16:20, James Clark james.clark@linaro.org wrote:
On 09/08/2024 3:13 pm, Mike Leach wrote:
Hi James
On Thu, 8 Aug 2024 at 10:32, James Clark james.clark@linaro.org wrote:
On 07/08/2024 5:48 pm, Leo Yan wrote:
Hi all,
On 8/7/2024 3:53 PM, James Clark wrote:
A minor suggestion: if the discussion is too long, please delete the irrelevant message ;)
[...]
--- a/tools/perf/scripts/python/arm-cs-trace-disasm.py +++ b/tools/perf/scripts/python/arm-cs-trace-disasm.py @@ -257,6 +257,11 @@ def process_event(param_dict): print("Stop address 0x%x is out of range [ 0x%x .. 0x%x ] for dso %s" % (stop_addr, int(dso_start), int(dso_end), dso)) return
if (stop_addr < start_addr):if (options.verbose == True):print("Packet Dropped, Discontinuity detected[stop_add:0x%x start_addr:0x%x ] for dso %s" % (stop_addr, start_addr, dso))
returnI suppose my only concern with this is that it hides real errors and Perf shouldn't be outputting samples that go backwards. Considering that fixing this in OpenCSD and Perf has a much wider benefit I think that should be the ultimate goal. I'm putting this on my todo list for now (including Steve's merging idea).
In the perf's util/cs-etm.c file, it handles DISCONTINUITY with:
case CS_ETM_DISCONTINUITY: /* * The trace is discontinuous, if the previous packet is * instruction packet, set flag PERF_IP_FLAG_TRACE_END * for previous packet. */ if (prev_packet->sample_type == CS_ETM_RANGE) prev_packet->flags |= PERF_IP_FLAG_BRANCH | PERF_IP_FLAG_TRACE_END;I am wandering if OpenCSD has passed the correct info so Perf decoder can detect the discontinuity. If yes, then the flag 'PERF_IP_FLAG_TRACE_END' will be set (it is a general flag in branch sample), then we can consider use it in the python script to handle discontinuous data.
No OpenCSD isn't passing the correct info here. Higher up in the thread I suggested an OpenCSD patch that makes it detect the error earlier and fixes the issue. It also needs to output a discontinuity when the address goes backwards. So two fixes and then the script works without modifications.
Which address is going backwards here? - OpenCSD generates trace ranges only by walking forwards from the last known address till it hits a branch. Unless this wraps round 0x000000 this will never result in a backwards address as far as I can see. Do you have an example dump with OpenCSD outputting a range packet with backwards addresses?
Mike
The example I have I think is something like this:
- Start address / trace on
- E
- Output range ...
- Periodic address update ...
- E
- Output range
If decode has gone wrong (but undetectably) between steps 1 and 3. Then the next steps still output a second range based on the last periodic address received. (I think it might not necessarily have to be a periodic address but could also be indirect address packet?). Perf converts the ranges into branch samples by taking the end of the first range and beginning of the second range. Then the disassembly script converts those samples into ranges again by taking the source and destination of the last two branch samples.
The original issue that Ganapat saw was that the periodic address causes OpenCSD to put the source address of the second range somewhere before the first one, even though it didn't output a branch or discontinuity that would explain how it got there.
But yes you're right the ranges themselves always go forwards from the point of view of their own start and end addresses.
I thought it might be possible for OpenCSD to check against the last range output? Although I wasn't sure if maybe it's actually valid to do a backwards jump like that without the trace on/off packets with address filtering or something?
The root cause is still the incorrect image, but I think this check along with the other direct branch check should make it pretty difficult for people to make the mistake.