Re: [PATCH] perf report powerpc: Fix crash if callchain is empty

[Ravi Bangoria]

On 06/11/2018 04:10 PM, Sandipan Das wrote:
> For some cases, the callchain provided by the kernel may be
> empty. So, the callchain ip filtering code will cause a crash
> if we do not check whether the struct ip_callchain pointer is
> NULL before accessing any members.
> 
> This can be observed on a powerpc64le system running Fedora 27
> as shown below.
> 
>   # perf record -b -e cycles:u ls
> 
> Before applying this patch:
> 
>   # perf report --branch-history
> 
>   perf: Segmentation fault
>   -------- backtrace --------
>   perf[0x1027615c]
>   linux-vdso64.so.1(__kernel_sigtramp_rt64+0x0)[0x7fff856304d8]
>   perf(arch_skip_callchain_idx+0x44)[0x10257c58]
>   perf[0x1017f2e4]
>   perf(thread__resolve_callchain+0x124)[0x1017ff5c]
>   perf(sample__resolve_callchain+0xf0)[0x10172788]
>   ...
> 
> After applying this patch:
> 
>   # perf report --branch-history
> 
>   Samples: 25  of event 'cycles:u', Event count (approx.): 2306870
>     Overhead  Source:Line            Symbol                   Shared Object
>   +   11.60%  _init+35736            [.] _init                ls
>   +    9.84%  strcoll_l.c:137        [.] __strcoll_l          libc-2.26.so
>   +    9.16%  memcpy.S:175           [.] __memcpy_power7      libc-2.26.so
>   +    9.01%  gconv_charset.h:54     [.] _nl_find_locale      libc-2.26.so
>   +    8.87%  dl-addr.c:52           [.] _dl_addr             libc-2.26.so
>   +    8.83%  _init+236              [.] _init                ls
>   ...
> 
> Reported-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>
> Signed-off-by: Sandipan Das <sandipan@xxxxxxxxxxxxx>


Acked-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxx>