[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 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
> 
> 
>> +               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