[PATCH V8 0/4] arm-cs-trace-disasm.py/perf must accommodate non-zero DSO text offset

Tue Oct 8 15:12:04 PDT 2024

On 10/8/2024 2:00 PM, Namhyung Kim wrote:
> On Tue, Oct 08, 2024 at 11:24:45AM -0700, Steve Clevenger wrote:
>>
>> Hello Namhyung,
>>
>> Sorry your question is so late. I don't include the ELF headers here,
>> but the problem can be seen with a perf.data packet dump of user
>> instruction trace capture. The problem is with the non-zero pgoff. The
>> arm-cs-trace-disasm.py script was never passed pgoff information to
>> adjust the start/end disassemble range passed to objdump. This patch
>> distributes the fix between perf and the arm-cs-trace-disasm.py script.
>>
>> Here's a brief excerpt from an e-mail I sent to James Clark describing
>> the patch before I submitted it.
> 
> Oh, is it applied to the coresight tree already?  I don't think I got
> any notification for that.  Please make sure to notify perf maintainers
> (and hopefullly to get Ack's) when you touch non-coresight part of the
> code.
> 
> Also I think we need to clarify how to route coresight tool patches.  I
> thought they are going through the perf-tools tree.  But it doesn't seem
> to be the case?
> 
> Anyway, sorry about being late on this.

FYI. These patch(es) were based on perf-tools-next at revision
6.11.0-rc3. All ack'd by Leo Yan. If they could get merged to
perf-tools, that would be great!

> 
>>
>> -----------------------------------------------------------------
>> .
>> .
>> This e-mail is to document what I know and don’t know about the problem.
>> The background is Fedora 38 introduced non-zero text offsets into common
>> shared objects and executables (e.g. libc.so.6, etc.).
>>
>> If you were to ‘perf report --dump’ the perf.data of a user mode
>> instruction trace on Fedora 37 and grep the PERF_RECORD_MMAP2 packets
>> you’ll notice all zero values (@ 0) for shared binary and executable
>> text offsets. Repeat the same for user trace collected on Fedora 38/39,
>> and these text offsets show as non-zero.
>>
>> Fedora 37:
>>
>> 4294967295 18446744073709551615 0x8ac8 [0x78]: PERF_RECORD_MMAP2
>> 2389577/2389577: [0xffff85124000(0x42000) @ 0 103:04 805306555
>> 1941233998]: r-xp /usr/lib/ld-linux-aarch64.so.1
>> 4294967295 18446744073709551615 0x8b40 [0x60]: PERF_RECORD_MMAP2
>> 2389577/2389577: [0xffff85161000(0x1000) @ 0 00:00 0 0]: r-xp [vdso]
>> 4294967295 18446744073709551615 0x8ba0 [0x68]: PERF_RECORD_MMAP2
>> 2389577/2389577: [0xaaaab09b0000(0x10000) @ 0 103:04 1140851919
>> 994218038]: r-xp /usr/bin/dd
>> 4294967295 18446744073709551615 0x8c08 [0x70]: PERF_RECORD_MMAP2
>> 2389577/2389577: [0xffff84f70000(0x1a9000) @ 0 103:04 1677721733
>> 3891973508]: r-xp /usr/lib64/libc.so.6
>>
>> Fedora 39:
>>
>> 4294967295 18446744073709551615 0x8ac8 [0x78]: PERF_RECORD_MMAP2
>> 18229/18229: [0xffffa5512000(0x1d000) @ 0x10000 103:04 161 4093340249]:
>> r-xp /usr/lib/ld-linux-aarch64.so.1
>> 4294967295 18446744073709551615 0x8b40 [0x60]: PERF_RECORD_MMAP2
>> 18229/18229: [0xffffa554f000(0x1000) @ 0 00:00 0 0]: r-xp [vdso]
>> 4294967295 18446744073709551615 0x8ba0 [0x68]: PERF_RECORD_MMAP2
>> 18229/18229: [0xaaaade7e0000(0xb000) @ 0x10000 103:04 536876423
>> 421616320]: r-xp /usr/bin/dd
>> 4294967295 18446744073709551615 0x8c08 [0x70]: PERF_RECORD_MMAP2
>> 18229/18229: [0xffffa5360000(0x11f000) @ 0x30000 103:04 536873199
>> 2415801053]: r-xp /usr/lib64/libc.so.6
>>
>> The arm-cs-trace-disasm.py script never gets to see the text offset into
>> the dso binaries, so has no opportunity to adjust the start/end address
>> range passed to objdump. This wasn’t a problem on Fedora 37 and below
>> since there’s no start/end adjustment for a zero text offset. On Fedora
>> 38/39 distros, the instruction trace shows unconditional branch
>> instructions which do not branch to the target address, the clearest
>> indication of trouble.
> 
> Ok, thanks for sharing this.  I'm ok with exposing pgoff to the python
> script itself.  But I'd like to make sure if it works correctly with
> PIEs that have non-zero page offsets in other places (probably ok).
> 
> Thanks,
> Namhyung
> 
> 
>> -----------------------------------------------------------------
>>
>> On 10/7/2024 10:51 PM, Namhyung Kim wrote:
>>> Hello,
>>>
>>> Sorry for the long delay.  But can you please explain your problem in
>>> more detail?  Showing ELF program (or section) header would be helpful
>>> as well.
>>>
>>> Is the problem when the text mapping has non-zero pgoff only?  Is the
>>> kernel symbols working correctly?  Or is it just the Python script
>>> broken?
>>>
>>> Thanks,
>>> Namhyung
>>>
>>> On Mon, Sep 09, 2024 at 03:30:02PM -0600, Steve Clevenger wrote:
>>>> Changes in V8:
>>>>   - in arm-cs-trace-disasm.py, ensure map_pgoff is not converted to
>>>>     string.
>>>>   - Remove map_pgoff integer conversion in dso not found print
>>>>     message.
>>>>
>>>> Changes in V7:
>>>>   - In arm-cs-trace-disasm.py, fix print message core dump resulting
>>>>     from mixed type arithmetic.
>>>>   - Modify CS_ETM_TRACE_ON filter to filter zero start_addr. The
>>>>     CS_ETM_TRACE_ON message is changed to print only in verbose mode.
>>>>   - Removed verbose mode only notification for start_addr/stop_addr
>>>>     outside of dso address range.
>>>>
>>>> Changes in V6:
>>>>   - In arm-cs-trace-disasm.py, zero map_pgoff for kernel files. Add
>>>>     map_pgoff to start/end address for dso not found message.
>>>>   - Added "Reviewed-by" trailer for patches 1-3 previously reviewed
>>>>     by Leo Yan in V4 and V5.
>>>>
>>>> Changes in V5:
>>>>   - In symbol-elf.c, branch to exit_close label if open file.
>>>>   - In trace_event_python.c, correct indentation. set_sym_in_dict
>>>>     call parameter "map_pgoff" renamed as "addr_map_pgoff" to
>>>>     match local naming.
>>>>
>>>> Changes in V4:
>>>>   - In trace-event-python.c, fixed perf-tools-next merge problem.
>>>>
>>>> Changes in V3:
>>>>   - Rebased to linux-perf-tools branch.
>>>>   - Squash symbol-elf.c and symbol.h into same commit.
>>>>   - In map.c, merge dso__is_pie() call into existing if statement.
>>>>   - In arm-cs-trace-disasm.py, remove debug artifacts.
>>>>
>>>> Changes in V2:
>>>>   - In dso__is_pie() (symbol-elf.c), Decrease indentation, add null pointer
>>>>     checks per Leo Yan review.
>>>>   - Updated mailing list distribution.
>>>>
>>>> Steve Clevenger (4):
>>>>   Add dso__is_pie call to identify ELF PIE
>>>>   Force MAPPING_TYPE__IDENTIY for PIE
>>>>   Add map pgoff to python dictionary based on MAPPING_TYPE
>>>>   Adjust objdump start/end range per map pgoff parameter
>>>>
>>>>  .../scripts/python/arm-cs-trace-disasm.py     | 17 ++++--
>>>>  tools/perf/util/map.c                         |  4 +-
>>>>  .../scripting-engines/trace-event-python.c    | 13 +++-
>>>>  tools/perf/util/symbol-elf.c                  | 61 +++++++++++++++++++
>>>>  tools/perf/util/symbol.h                      |  1 +
>>>>  5 files changed, 86 insertions(+), 10 deletions(-)
>>>>
>>>> -- 
>>>> 2.44.0
>>>>
>>