perf libdw: Optimize fallback logic for missing DWARF

When libdw encounters a DWARF definition it cannot accurately un-inline
or an address block natively missing structural line maps,
dwfl_module_getsrc() returns NULL.

Previously, libdw__addr2line() returned -1 in both dwfl_module_getdwarf()
and dwfl_module_getsrc() failure paths while addr2line() in srcline.c
only stopped its fallback loop on ret > 0.

This caused perf's addr2line_style loop to fall back to llvm, libbfd,
and the cmd__addr2line() subprocess wrapper on every unmapped address or
stripped DSO.

Update the addr2line_style pipeline return semantics consistently:

1. Backends return 0 to denote conclusively missing information
   (e.g. valid ELF but no DWARF inside, or parsed DWARF with no mapped
   lines), stopping the fallback loop.

2. Backends (and uncompiled stubs) return < 0 to denote initialization
   or backend errors, instructing the loop to iterate to the next
   configured fallback.

3. Backends return > 0 on successful source line resolution.

Fixes: bf96e296d52d74a1 ("perf libdw: Fix Dwfl discovery with split files")
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alessio Podda <aleph.pi.gh@gmail.com>
Cc: Alireza Haghdoost <haghdoost@uber.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Michael Liang <mliang@purestorage.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shimin Guo <shimin.guo@skydio.com>
Cc: Tanushree Shah <tshah@linux.ibm.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

0 files changed, 0 insertions, 0 deletions