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

[Jiri Olsa <jolsa@redhat.com>]

On Fri, Nov 02, 2018 at 10:55:16AM +0800, leo.yan@linaro.org 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:

yep, AFAIK if there's no vmlinux found we fallback to /proc/kallsyms

> 
>   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()

so what is the actual error you see in the perf script?
unresolved samples? could you please describe your config
and workload?

thanks,
jirka

> 
> 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