The addr2line command is started and then addresses piped to it. In
order to determine the end of a addr2lines output a ',' it output with
an expectation to get '??\n??:0\n' as a reply. llvm-addr2line differs
in that ',' generates a reply of ','.

The approach detects and then caches the addr2line style. When records
are read the sentinel is detected appropriately.

Comparing the output there is a little more inline data on my machine
with llvm-addr2line:
$ sudo perf record -a -g sleep 1
$ sudo perf report --addr2line=addr2line > a.txt
$ sudo perf report --addr2line=llvm-addr2line > b.txt
$ wc -l a.txt b.txt
  12386 a.txt
  12477 b.txt

Some other small changes, switching to the api/io code to avoid file
streams wrapping the command's stdin/stdout. Ignore SIGPIPE for when
addr2line exits and writes fail.

Ian Rogers (4):
  tools api: Add io__getline
  perf srcline: Simplify addr2line subprocess
  perf srcline: Support for llvm-addr2line
  perf srcline: Avoid addr2line SIGPIPEs

 tools/lib/api/io.h        |  40 ++++++++++
 tools/perf/tests/api-io.c |  36 +++++++++
 tools/perf/util/srcline.c | 162 +++++++++++++++++++++++---------------
 3 files changed, 174 insertions(+), 64 deletions(-)

-- 
2.40.0.348.gf938b09366-goog