Hi Mike,
Thanks for your patience and exceptional response!
________________________________ From: Mike Leach mike.leach@linaro.org Sent: 11 July 2019 17:04 To: Student - Ng Yi Zher Jeremy jeremy_ng@mymail.sutd.edu.sg Cc: Leo Yan leo.yan@linaro.org; Coresight ML coresight@lists.linaro.org Subject: Re: Request for Guidance in Using sysFS for Coresight in HiKey960 (Cortex A53/A73)
Hi Jeremy,
Unfortunately my previous mail appears to have been affected by some formatting problems by my webmail client, so is incomplete. Thank you for getting back to me! 🙂
On Wed, 10 Jul 2019 at 16:07, Mike Leach mike.leach@linaro.org wrote:
retHello Jeremy,
On Wed, 10 Jul 2019 at 10:06, Student - Ng Yi Zher Jeremy jeremy_ng@mymail.sutd.edu.sg wrote:
Dear Sir,
Please look at inline comments for my reply.
My apologies for such a late reply.
From: Leo Yan leo.yan@linaro.org Sent: 10 June 2019 17:32 To: Student - Ng Yi Zher Jeremy Cc: Mathieu Poirier; Suzuki K Poulose; Coresight ML Subject: Re: Request for Guidance in Using sysFS for Coresight in HiKey960 (Cortex A53/A73)
Hi Jeremy,
Please see several quick inline comments.
On Mon, Jun 10, 2019 at 08:49:48AM +0000, Student - Ng Yi Zher Jeremy wrote:
[...]
-rw-r--r-- 1 root root 4096 1970-01-01 00:11 ecc40000.etm/addr_start hikey960:/sys/bus/coresight/devices # echo d10583ff > ecc40000.etm/addr_start 1|hikey960:/sys/bus/coresight/devices # cat ecc40000.etm/addr_start cat: ecc40000.etm/addr_start: Operation not permittedAfter read the code, I think you need firstly to specify addr_idx:
echo 3 > ecc40000.etm/addr_idx echo d10583ff > ecc40000.etm/addr_start cat ecc40000.etm/addr_start
I did as per your instruction. I was wondering if it is normal that once I specified a value for addr_start, I am unable to insert a value into addr_stop.
An example of the snippet is found here:
hikey960: # echo 3 > addr_idx hikey960: # cat addr* addr_context: 0x0 addr_ctxtype: none addr_idx: 0x3 addr_instdatatype: instr cat: addr_range: Operation not permitted addr_single: 0x0 addr_start: 0x0 addr_stop: 0x0
hikey960: # echo 0x55555557b0 > addr_start hikey960: # cat addr* addr_context: 0x0 addr_ctxtype: none addr_idx: 0x3 addr_instdatatype: instr cat: addr_range: Operation not permitted addr_single: Operation not permitted addr_start: 0x55555557b0 addr_stop: Operation not permitted
I thought it was not important that the Operation was 'not permitted'. Nonetheless, I continued with the tutorial as depicted [here](https://github.com/torvalds/linux/blob/master/Documentation/trace/coresight....). One thing I will like to note is that my `rwp` did move when i initially activated the sink and source. However, the 2nd time i checked the `rwp`, it went back `0x0`, the same position as that of my `rrp`.
Regardless, I run the program in another kernel, performed CPU affinity to the program to point at the CPU in which the ETM is activated (in this case, CPU0). While the program is running, i looked at the `rwp/rrp` and see that neither of the pointers are moving. I thought perhaps if i perform `dd` operation, I might be able to get something.
I performed `dd if=/dev/ec036000.etf of=/data/cs.bin bs=1M` but my device crashed and reboot itself without saving any files.
Could you try below commands before dd command?
echo 1 > /sys/bus/coresight/devices/ec036000.etf # Enable ETM for CPU0 echo 1 > /sys/bus/coresight/devices/ecc40000.etm/enable_source dd if=/dev/ec036000.etf of=/data/cs.bin bs=1M
Please note, you need firstly configure the address range, and then enable the ETM and sink. If afterwards change the address range again, you need disable etf/etm and re-enable etf/etm so can set address range configuration into registers properly.
I have also tried your above suggestion. Currently, I find addr_start and addr_stop traces to better fit what I want rather than addr_range. addr_start and addr_stop will be able to capture traces of what the system perform in terms of context switches, what syscalls it makes, etc.
Regardless, I have tried addr_range and I was able to acquire some traces from my program. I will like to share with you some of my findings because I find the result of the traces to be peculiar in what it has chosen to trace and ignore.
I have switched off ASLR, so I am under the assumption that the instruction address from trace dumps should be similar to that of GDB
=== simple_math_function1.c === void math(int *i){ (*i)++; (*i)++; (*i)++; (*i)++; }
main(int i){ // many function calls, loop once while (i <= 20){ math(&i); math(&i); math(&i); math(&i); math(&i); printf("%d\n",i); } } =======================
this is a snippet of my decoded trace log: Address - Instruction address 0x0000005555555cf4, Instruction set Aarch32 (Thumb) Address - Instruction address 0x0000005555555cfc, Instruction set Aarch32 (Thumb) Address - Instruction address 0x0000005555555d04, Instruction set Aarch32 (Thumb) Address - Instruction address 0x0000005555555d0c, Instruction set Aarch32 (Thumb) Address - Instruction address 0x0000005555555d14, Instruction set Aarch32 (Thumb)
compared against GDB: |0x5555555cf4 <main+972> ldr x0, [sp,#64] |0x5555555cf8 <main+976> bl 0x55555558d8 <math> |0x5555555cfc <main+980> ldr x0, [sp,#64] |0x5555555d00 <main+984> bl 0x55555558d8 <math> |0x5555555d04 <main+988> ldr x0, [sp,#64] |0x5555555d08 <main+992> bl 0x55555558d8 <math> |0x5555555d0c <main+996> ldr x0, [sp,#64] |0x5555555d10 <main+1000> bl 0x55555558d8 <math> |0x5555555d14 <main+1004> ldr x0, [sp,#64]
Please remember that the decode you are seeing is the decode of trace packets, not full trace decode. Addresses that appear in the packets represent addresses that cannot be deduced otherwise from analysing the program image. No other addresses will appear as part of the trace. Therefore the series of addresses that appear to refer to the LDR instructions above, tell the trace decoder where execution resumes after the return from the "math" routine. The BL instruction requires no address element in the trace as the branch target can be deduced directly from the instructions.
Thank you for explaining this to me. I thought it was rather peculiar and I have been reading the ETMv4 TRM over and over again but I could not understand how the ETM was choosing what instructions to trace.
Unfortunately, I have never done tracing before this and the learning curve might have been extraordinary for me at this stage.
comparing the gdb and trace dumps, it seems to only trace ldr and ignore bl instructions.
this is the 2nd program, just a slight tweak from the above program:
=== simple_math_function2.c === void math(int *i){ (*i)++; (*i)++; (*i)++; (*i)++; }
main(int i){ // 1 function call, looped many times while (i <= 20){ math(&i); printf("%d\n",i); } } ======================= trace dump:
Address - Instruction address 0x0000005555555b9c, Instruction set Aarch32 (Thumb) ATOM - E Commit - 1 Address - Instruction address 0x0000005555555b9c, Instruction set Aarch32 (Thumb) ATOM - E Commit - 1 Address - Instruction address 0x0000005555555b9c, Instruction set Aarch32 (Thumb) ATOM - E Commit - 1 Address - Instruction address 0x0000005555555b9c, Instruction set Aarch32 (Thumb) ATOM - E Commit - 1 Address - Instruction address 0x0000005555555b9c, Instruction set Aarch32 (Thumb) ATOM - E Commit - 1
gdb log:
|0x5555555b94 <main+620> ldr x0, [sp,#64] |0x5555555b98 <main+624> bl 0x55555558d8 <math> |0x5555555b9c <main+628> b 0x5555555b78 <main+592> |0x5555555ba0 <main+632> ldr x8, [sp,#64]
Again the 0x0000005555555b9c addresses represent the return from the math routine, and not trace for the b 0x5555555b78 <main+592> instruction This b 0x0x5555555b78 is likely represented by the E atom
There is some concern regarding the classification of the AArch32 code as thumb - it would seem from the assembly code that the
What this should have said was that the assembly code appears to be AArch64 code - registers Xn are an indicator of this. However the decoder you are using appears to be classifying that addresses as AArch32 & Thumb. This could be an issue with the decoder - how are you compiling the code? Is it AArch64? Yes, it is actually AArch64. I cross-compiled my programs with android-ndk-20r. I was puzzled with the decoder and I have had my suspicions on the decoding tool as well. I am recently looking closer at the source code of ptm2human in case it might have wrongly classified my trace packets.
These relationships are explained in the ETMv4 TRM - Appendix A, examples of trace.
Regards
Mike
This time, i notice that the etm only trace the `b` instructions but not the `ldr` instructions.
I am rather puzzled by the outcome of the traces as I could not understand why the result might be different for a somewhat similar code...
I don't try at my side, if have any question or issue, please report back so I can test on Hikey960.
Thanks, Leo Yan
Thank you very much for your kindness and assistance the last time!
Also, one last question: I will like to ask how I might be able to activate global timestamp for instruction trace? i noticed trcidr0 supports timestamp (tssize of 64 bits). However, trcconfigr have disabled all my options. Is there a workaround this?
Since perf is still not supported in android, i have been using ptm2human to decode etm dumps. I am also wondering if there are other decoders that I have not explored? From what I have seen, DS-5 seems to request DSTREAM to activate ETM trace and decode the trace dumps. I tried to do it without the DSTREAM and DS-5 was unable to recognise the trace dumps.
Have you looked at OpenCSD (https://github.com/Linaro/OpenCSD) ? This is a trace decode library that will do full decode as well as the packet decode provided by ptm2human.
Regards
Mike I have taken a peek at OpenCSD previously. But there seems to be more documentations on using OpenCSD integrated with perf than using the libraries standalone.
I might also have confused myself when I saw that the trace decoder will not work if OpenCSD is not integrated with perf from a conference slide made by Mathieu Poirier.
I have attached an image grab from the slide with the line highlighted for easy reference.
[cid:209fcf2f-9674-44ce-b668-42c0203a6c20] reference: https://elinux.org/images/b/b3/Hardware_Assisted_Tracing_on_ARM.pdf
I will love to explore OpenCSD as well. I tinkered it slightly this morning and it seems that a snapshot of the device is required. I am still trying to understand how I might be able to trace and decode with OpenCSD and also how I might be able to obtain a snapshot of my device.
With ptm2human, I am merely extracting the etm dumps from the sinks by using the dd command, extract the trace dump from target device (hikey960 - android) to host device (linux-x86_64) and decode the binary files into a decoded trace file.
Any help will be greatly appreciated!
Sincerely, Jeremy
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CoreSight mailing list CoreSight@lists.linaro.org https://lists.linaro.org/mailman/listinfo/coresight
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK
I will like to also ask how I might be able to change some trcconfig settings. it is found in *.etm/mgmt/trcconfig and it is a read-only file.
I have tried to change the settings through memory mapping and searched for other ways through tweaking with the driver files in drivers/hwtracing/coresight/coresight-etm4x.c
I have been wanting to activate timestamps and/or branch broadcast. In all honesty, I am still trying to understand what exactly branch broadcast is as well.
Really sorry to have bothered you with mediocre and amateurish questions.
Yours Sincerely, Jeremy
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