Re: Question: perf dso support for /proc/kallsyms

[Mike Leach]

Hi Leo,

My understanding is that when we decode CoreSight trace - be it on the
system that generated it, or off target device on a separate host
system, we are using the dso files in .debug/ as these represent the
memory layout at the time trace was recorded.

If I look into a recent session copied up to my linux box from DB410,
is see ~/.debug/\[kernel.kallsyms\]/ee80c1f3a434469f6174e1cf4bb5583d83a013dc/kallsyms
- which seems to me to be the relevant symbol file to use rather than
the live one generated by /proc/kallsyms. I don't really want to use
the local /proc/kallsyms on my x86 linux box when decoding an ARM
trace captured elsewhere.

So perhaps the problem to be solved is not how to use /proc/kallsyms
if no vmlinux is supplied to the script, but ensure that the
[kernel.kallsyms] is used?

Regards

Mike
On Fri, 2 Nov 2018 at 02:55, <leo.yan@xxxxxxxxxx> wrote:
>
> Hi all,
>
> Now I found that if use the command 'perf script' for Arm CoreSight trace
> data, it fails to parse kernel symbols if we don't specify kernel vmlinux
> file.   So when we don't specify kernel symbol files then perf tool will
> roll back to use /proc/kallsyms for kernel symbols parsing, as result it will
> run into below flow:
>
>   thread__find_addr_map(thread, cpumode, MAP__FUNCTION, address, &al);
>   map__load(al.map);
>   dso__data_read_offset(al.map->dso, machine, offset, buffer, size);
>     `-> data_read_offset()
>
> I can observe the function data_read_offset() returns failure, this is caused
> by checking the offset sanity "if (offset > dso->data.file_size)"  (I pasted
> the whole function code at below in case you want to get more context for it),
> but if perf use "/proc/kallsyms" to load kernel symbols, the variable
> 'dso->data.file_size' will be set to zero thus the sanity checking always
> thinks the offset is out of the file size bound.
>
> Now I still don't understand how the dso/map support "/proc/kallsyms" and
> have no idea to fix this issue, though I spent some time to look into it.
>
> Could you give some suggestion for this?  Or even better if you have fixing
> for this, I am glad to test at my side.
>
> static ssize_t data_read_offset(struct dso *dso, struct machine *machine,
>                                 u64 offset, u8 *data, ssize_t size)
> {
>         if (data_file_size(dso, machine))
>                 return -1;
>
>         /* Check the offset sanity. */
>         if (offset > dso->data.file_size)
>                 return -1;
>
>         if (offset + size < offset)
>                 return -1;
>
>         return cached_read(dso, machine, offset, data, size);
> }
>
> Thanks,
> Leo Yan
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-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK