perf powerpc: Unify the skip-callchain-idx libdw with that for addr2line

2026-01-20T16:04:38+00:00

Rather than have 2 Dwfl unify the Dwfl in skip-callchain-idx with that
is used by libdw__addr2line().

Rename that variable in 'struct dso' from 'a2l_libdw' to just 'libdw' as
it is now used in more than addr2line.

The Dwfl in skip-callchain-idx uses a map address when being read with
dwfl_report_elf (rather than dwfl_report_offline that addr2line
uses).

skip-callchain-idx is wrong as the map address can vary between
processes because of ASLR, ie it should need a different Dwfl per
process.

In the code after this patch the base address becomes 0 and the mapped
PC is used with the dwfl functions.

This should increase the accuracy of skip-callchain-idx, but the impact
has only been build tested.

Signed-off-by: Ian Rogers 
Cc: Aditya Bodkhe 
Cc: Adrian Hunter 
Cc: Albert Ou 
Cc: Alexandre Ghiti 
Cc: Andi Kleen 
Cc: Athira Rajeev 
Cc: Chun-Tse Shao 
Cc: Dmitriy Vyukov 
Cc: Dr. David Alan Gilbert 
Cc: Guo Ren 
Cc: Haibo Xu 
Cc: Howard Chu 
Cc: Ingo Molnar 
Cc: James Clark 
Cc: Jiri Olsa 
Cc: John Garry 
Cc: Krzysztof Łopatowski 
Cc: Leo Yan 
Cc: Mark Wielaard 
Cc: Namhyung Kim 
Cc: Palmer Dabbelt 
Cc: Paul Walmsley 
Cc: Peter Zijlstra 
Cc: Sergei Trofimovich 
Cc: Shimin Guo 
Cc: Stephen Brennan 
Cc: Thomas Falcon 
Cc: Will Deacon 
Signed-off-by: Arnaldo Carvalho de Melo

perf addr2line: Add a libdw implementation

2026-01-12T19:23:06+00:00

Add an implementation of addr2line that uses libdw.

Other addr2line implementations are slow, particularly in the case of
forking addr2line.

Add an implementation that caches the libdw information in the dso and
uses it to find the file and line number information.

Inline information is supported but because cu_walk_functions_at visits
the leaf function last add a inline_list__append_tail to reverse the
lists order.

Committer testing:

  # perf probe -x ~/bin/perf libdw__addr2line
  Added new event:
    probe_perf:libdw_addr2line (on libdw__addr2line in /home/acme/bin/perf)

  You can now use it in all perf tools, such as:

  	perf record -e probe_perf:libdw_addr2line -aR sleep 1

  #
  # perf stat -e probe_perf:libdw_addr2line perf report -f --dso perf --stdio -s srcfile,srcline
  # To display the perf.data header info, please use --header/--header-only options.
  #
  #
  # Total Lost Samples: 0
  #
  # Samples: 4K of event 'cpu/cycles/Pu'
  # Event count (approx.): 5535180842
  #
  # Overhead  Source File   Source:Line
  # ........  ............  ...............
  #
      99.04%  inlineloop.c  inlineloop.c:21
       0.46%  inlineloop.c  inlineloop.c:20

  #
  # (Tip: For tracepoint events, try: perf report -s trace_fields)
  #

   Performance counter stats for 'perf report -f --dso perf --stdio -s srcfile,srcline':

                  44      probe_perf:libdw_addr2line

         0.037260744 seconds time elapsed

         0.025299000 seconds user
         0.011918000 seconds sys
  #

Adding probes to the other addr2line implementations (llvm__addr2line,
libbfd__addr2line and cmd__addr2line) I noticed some fallbacks to the
llvm one:

 Performance counter stats for 'perf report -f --dso perf --stdio -s srcfile,srcline':

                44      probe_perf:libdw_addr2line
                23      probe_perf:llvm_addr2line
                 0	probe_perf:libbfd_addr2line
                 0      probe_perf:cmd_addr2line

Something to investigate further, but at least we don't fallback to the
cmd based one :-)

Reviewed-by: James Clark 
Signed-off-by: Ian Rogers 
Tested-by: Arnaldo Carvalho de Melo 
Cc: Adrian Hunter 
Cc: Alexander Shishkin 
Cc: Howard Chu 
Cc: Ingo Molnar 
Cc: Jiri Olsa 
Cc: Namhyung Kim 
Cc: Peter Zijlstra 
Cc: Stephen Brennan 
Cc: Tony Jones 
Signed-off-by: Arnaldo Carvalho de Melo

linux.git/tools/perf/util/libdw.h, branch master

perf powerpc: Unify the skip-callchain-idx libdw with that for addr2line

perf addr2line: Add a libdw implementation