[RFC] perf: Dwarf cfi based user callchains

[Frederic Weisbecker <fweisbec@gmail.com>]

Hi,

This brings dwarf cfi based callchain for userspace apps that don't have
frame pointers.

To test it, you can try:

perf record -g dwarf,24000 -e cycles:u ./hackbench 2
perf report

It seems to work but there are of course many things to improve:

- do only userspace profiling with that mode for now (the :u flag as above).
  The reason is that if you profile also the kernel, the user callchains
  will often start from vdso if the user made a syscall, and vdso doesn't
  have cfi informations, so we get stuck there. I need to find a solution for
  that, like doing a single frame pointer deref on the first entry (vdso)
  and continue with dwarves, but I need to know if we came from a syscall for
  that. Not sure yet how I'll handle that.

- it only works with .eh_frame, I think there is an elf section that is made
  almost the same but with few differences. I don't remember the name at that
  time but that needs a look.

- it's slow. A first improvement to make it faster is to support binary
  search from .eh_frame_hdr. This will probably be one of the next things
  I'll focus in. And the whole needs perhaps more caching and so on.

- only support for x86-32. I need to split some arch specific code from
  generic and add at least x86-64 support.

- there are still some callchains that are not unwind. I need to investigate.

This can be found in:

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing.git
	perf/unwind-v1

Thanks,
	Frederic
---

Frederic Weisbecker (9):
      uaccess: Make copy_from_user_nmi() globally available
      perf: Add ability to dump user regs
      perf: Add ability to dump part of the user stack
      perf: Don't record frame pointer based user stacktraces if we dump stack and regs
      perf: Support for dwarf mode callchain on perf record
      perf: Build with dwarf cfi
      perf: Support for error passed over pointers
      perf: Add libunwind dependency for dwarf cfi unwinding
      perf: Support for dwarf cfi unwinding on post processing


 arch/x86/include/asm/uaccess.h      |    5 +
 arch/x86/kernel/cpu/perf_event.c    |    4 +-
 include/asm-generic/uaccess.h       |    4 +
 include/linux/perf_event.h          |   15 +-
 kernel/perf_event.c                 |  182 +++++-
 tools/perf/Makefile                 |   23 +-
 tools/perf/builtin-record.c         |   76 +++-
 tools/perf/builtin-report.c         |    9 +-
 tools/perf/feature-tests.mak        |   14 +
 tools/perf/perf.h                   |    5 +
 tools/perf/util/callchain.c         |   35 +-
 tools/perf/util/callchain.h         |   19 +-
 tools/perf/util/event.c             |   29 +
 tools/perf/util/event.h             |    7 +
 tools/perf/util/include/linux/err.h |   24 +
 tools/perf/util/unwind.c            | 1077 +++++++++++++++++++++++++++++++++++
 16 files changed, 1485 insertions(+), 43 deletions(-)