[RFC] perf: Dwarf cfi based user callchains

Frederic Weisbecker
2010-10-13T05:07:09Z

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(-)