Re: [RESEND PATCH v6 0/8] perf: Support searching local debugging vdso or specify vdso path in cmdline

[YinFengwei]

Hi Changbin,

On Fri, Aug 16, 2024 at 06:58:03PM +0800, Changbin Du wrote:
> The vdso dumped from process memory (in buildid-cache) lacks debugging
> info. To annotate vdso symbols with source lines we need a debugging
> version.
> 
> For x86, we can find them from your local build as
> 'arch/x86/entry/vdso/vdso{32,64}.so.dbg'. Or they may resides in
> '/lib/modules/<version>/vdso/vdso{32,64}.so' on Ubuntu. But notice that the
> builid has to match.
> 
> If user doesn't specify the path, perf will search them internally as long
> as vmlinux when recording samples. The searched debugging vdso will add to
> buildid cache as ~/.debug/[vdso]/debug.
> 
> Below samples are captured on my local build kernel. perf succesfully
> find debugging version vdso and we can annotate with source without
> specifying vdso path.
> 
> $ sudo perf record -a
> $ sudo perf report --objdump=llvm-objdump
> 
> Samples: 17K of event 'cycles:P', 4000 Hz, Event count (approx.): 1760
> __vdso_clock_gettime  /work/linux-host/arch/x86/entry/vdso/vdso64.so.d
> Percent│       movq    -48(%rbp),%rsi
>        │       testq   %rax,%rax
>        │     ;               return vread_hvclock();
>        │       movq    %rax,%rdx
>        │     ;               if (unlikely(!vdso_cycles_ok(cycles)))
>        │     ↑ js      eb
>        │     ↑ jmp     74
>        │     ;               ts->tv_sec = vdso_ts->sec;
>   0.02 │147:   leaq    2(%rbx),%rax
>        │       shlq    $4, %rax
>        │       addq    %r10,%rax
>        │     ;               while ((seq = READ_ONCE(vd->seq)) & 1) {
>   9.38 │152:   movl    (%r10),%ecx
> 
> When doing cross platform analysis, we need to specify the vdso path manually if
> we are interested in its symbols, because they are not installed on local
> machine. At most two vdso can be given. Also you can pack your buildid cache with
> perf-archive if the debugging vdso can be found on the sampled machine.
> 
> $ sudo perf report --objdump=llvm-objdump \
>       --vdso arch/x86/entry/vdso/vdso64.so.dbg,arch/x86/entry/vdso/vdso32.so.dbg
With latest upstream kernel, I still can't annotate symbols in vdso.
With your patch and this --vdso command, it works great on x86 and arm64
platform. So
   Tested-by: Yin Fengwei <fengwei_yin@xxxxxxxxxxxxxxxxx>


Regards
Yin, Fengwei

> 
> I also improved perf-buildid-cache command to recognize vdso when adding files,
> then place it at correct place.
> 
> $ sudo perf buildid-cache --add /work/linux/arch/x86/entry/vdso/vdso64.so.dbg