[PATCH V4 2/2] tools/perf/tests: Fix object code reading to skip address that falls out of text section

[Athira Rajeev]

> On 27-Sep-2023, at 8:25 PM, Athira Rajeev <atrajeev at linux.vnet.ibm.com> wrote:
> 
> 
> 
>> On 27-Sep-2023, at 5:45 AM, Namhyung Kim <namhyung at kernel.org> wrote:
>> 
>> On Thu, Sep 14, 2023 at 10:40 PM Athira Rajeev
>> <atrajeev at linux.vnet.ibm.com> wrote:
>>> 
>>> The testcase "Object code reading" fails in somecases
>>> for "fs_something" sub test as below:
>>> 
>>>   Reading object code for memory address: 0xc008000007f0142c
>>>   File is: /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko
>>>   On file address is: 0x1114cc
>>>   Objdump command is: objdump -z -d --start-address=0x11142c --stop-address=0x1114ac /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko
>>>   objdump read too few bytes: 128
>>>   test child finished with -1
>>> 
>>> This can alo be reproduced when running perf record with
>>> workload that exercises fs_something() code. In the test
>>> setup, this is exercising xfs code since root is xfs.
>>> 
>>>   # perf record ./a.out
>>>   # perf report -v |grep "xfs.ko"
>>>     0.76% a.out /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko  0xc008000007de5efc B [k] xlog_cil_commit
>>>     0.74% a.out  /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko  0xc008000007d5ae18 B [k] xfs_btree_key_offset
>>>     0.74% a.out  /lib/modules/6.5.0-rc3+/kernel/fs/xfs/xfs.ko  0xc008000007e11fd4 B [k] 0x0000000000112074
>>> 
>>> Here addr "0xc008000007e11fd4" is not resolved. since this is a
>>> kernel module, its offset is from the DSO. Xfs module is loaded
>>> at 0xc008000007d00000
>>> 
>>>  # cat /proc/modules | grep xfs
>>>   xfs 2228224 3 - Live 0xc008000007d00000
>>> 
>>> And size is 0x220000. So its loaded between  0xc008000007d00000
>>> and 0xc008000007f20000. From objdump, text section is:
>>>   text 0010f7bc  0000000000000000 0000000000000000 000000a0 2**4
>>> 
>>> Hence perf captured ip maps to 0x112074 which is:
>>> ( ip - start of module ) + a0
>>> 
>>> This offset 0x112074 falls out .text section which is up to 0x10f7bc
>>> In this case for module, the address 0xc008000007e11fd4 is pointing
>>> to stub instructions. This address range represents the module stubs
>>> which is allocated on module load and hence is not part of DSO offset.
>>> 
>>> To address this issue in "object code reading", skip the sample if
>>> address falls out of text section and is within the module end.
>>> Use the "text_end" member of "struct dso" to do this check.
>>> 
>>> To address this issue in "perf report", exploring an option of
>>> having stubs range as part of the /proc/kallsyms, so that perf
>>> report can resolve addresses in stubs range
>>> 
>>> However this patch uses text_end to skip the stub range for
>>> Object code reading testcase.
>>> 
>>> Reported-by: Disha Goel <disgoel at linux.ibm.com>
>>> Signed-off-by: Athira Rajeev <atrajeev at linux.vnet.ibm.com>
>>> Tested-by: Disha Goel<disgoel at linux.ibm.com>
>>> Reviewed-by: Adrian Hunter <adrian.hunter at intel.com>
>>> ---
>>> Changelog:
>>> v3 -> v4:
>>> Fixed indent in V3
>>> 
>>> v2 -> v3:
>>> Used strtailcmp in comparison for module check and added Reviewed-by
>>> from Adrian, Tested-by from Disha.
>>> 
>>> v1 -> v2:
>>> Updated comment to add description on which arch has stub and
>>> reason for skipping as suggested by Adrian
>>> 
>>> tools/perf/tests/code-reading.c | 10 ++++++++++
>>> 1 file changed, 10 insertions(+)
>>> 
>>> diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
>>> index ed3815163d1b..9e6e6c985840 100644
>>> --- a/tools/perf/tests/code-reading.c
>>> +++ b/tools/perf/tests/code-reading.c
>>> @@ -269,6 +269,16 @@ static int read_object_code(u64 addr, size_t len, u8 cpumode,
>>>       if (addr + len > map__end(al.map))
>>>               len = map__end(al.map) - addr;
>>> 
>>> +       /*
>>> +        * Some architectures (ex: powerpc) have stubs (trampolines) in kernel
>>> +        * modules to manage long jumps. Check if the ip offset falls in stubs
>>> +        * sections for kernel modules. And skip module address after text end
>>> +        */
>>> +       if (!strtailcmp(dso->long_name, ".ko") && al.addr > dso->text_end) {
>> 
>> There's a is_kernel_module() that can check compressed modules
>> too but I think we need a simpler way to check it like dso->kernel.
>> 
>> Thanks,
>> Namhyung
> 
> Thanks for the comment Namhyung. I will add similar to dso->kernel, another field check in next version of patchset
> 
> Athira

Hi Namhyung,

I have posted a V5 for this:
https://lore.kernel.org/linux-perf-users/20230928075213.84392-1-atrajeev@linux.vnet.ibm.com/T/#t

Thanks
Athira
>> 
>> 
>>> +               pr_debug("skipping the module address %#"PRIx64" after text end\n", al.addr);
>>> +               goto out;
>>> +       }
>>> +
>>>       /* Read the object code using perf */
>>>       ret_len = dso__data_read_offset(dso, maps__machine(thread__maps(thread)),
>>>                                       al.addr, buf1, len);
>>> --
>>> 2.31.1