linux/tools
Ravi Bangoria 99e608b595 perf probe ppc64le: Fix probe location when using DWARF
Powerpc has Global Entry Point and Local Entry Point for functions.  LEP
catches call from both the GEP and the LEP. Symbol table of ELF contains
GEP and Offset from which we can calculate LEP, but debuginfo does not
have LEP info.

Currently, perf prioritize symbol table over dwarf to probe on LEP for
ppc64le. But when user tries to probe with function parameter, we fall
back to using dwarf(i.e. GEP) and when function called via LEP, probe
will never hit.

For example:

  $ objdump -d vmlinux
    ...
    do_sys_open():
    c0000000002eb4a0:       e8 00 4c 3c     addis   r2,r12,232
    c0000000002eb4a4:       60 00 42 38     addi    r2,r2,96
    c0000000002eb4a8:       a6 02 08 7c     mflr    r0
    c0000000002eb4ac:       d0 ff 41 fb     std     r26,-48(r1)

  $ sudo ./perf probe do_sys_open
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060904

  $ sudo ./perf probe 'do_sys_open filename:string'
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060896 filename_string=+0(%gpr4):string

For second case, perf probed on GEP. So when function will be called via
LEP, probe won't hit.

  $ sudo ./perf record -a -e probe:do_sys_open ls
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.195 MB perf.data ]

To resolve this issue, let's not prioritize symbol table, let perf
decide what it wants to use. Perf is already converting GEP to LEP when
it uses symbol table. When perf uses debuginfo, let it find LEP offset
form symbol table. This way we fall back to probe on LEP for all cases.

After patch:

  $ sudo ./perf probe 'do_sys_open filename:string'
  $ sudo cat /sys/kernel/debug/tracing/kprobe_events
    p:probe/do_sys_open _text+3060904 filename_string=+0(%gpr4):string

  $ sudo ./perf record -a -e probe:do_sys_open ls
    [ perf record: Woken up 1 times to write data ]
    [ perf record: Captured and wrote 0.197 MB perf.data (11 samples) ]

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1470723805-5081-2-git-send-email-ravi.bangoria@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
2016-08-09 12:14:29 -03:00
..
arch tools: Sync cpufeatures headers with the kernel 2016-08-09 11:56:33 -03:00
build perf build: Add sdt feature detection 2016-07-13 23:09:09 -03:00
cgroup
firewire
gpio tools/gpio: add install section 2016-06-23 11:07:13 +02:00
hv tools: hv: Add a script to help bonding synthetic and VF NICs 2016-07-12 10:41:53 -07:00
iio iio: generic_buffer: Fix --trigger-num option 2016-06-11 17:38:06 +01:00
include toops: Sync tools/include/uapi/linux/bpf.h with the kernel 2016-08-09 11:48:07 -03:00
kvm/kvm_stat tools: kvm_stat: Add comments 2016-05-25 16:12:06 +02:00
laptop/freefall Move freefall program from Documentation/ to tools/ 2015-06-08 16:42:07 -06:00
lguest tools/lguest: Force disable tboot and APM 2016-04-22 10:29:03 +02:00
lib perf/core improvements and fixes: 2016-08-04 11:02:38 +02:00
net tools: bpf_jit_disasm: check for klogctl failure 2016-05-08 23:32:59 -04:00
nfsd
objtool Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2016-07-30 11:54:53 -07:00
perf perf probe ppc64le: Fix probe location when using DWARF 2016-08-09 12:14:29 -03:00
power ACPI material for v4.8-rc1 2016-07-26 17:56:45 -07:00
scripts tools build: Fix objtool build with ARCH=x86_64 2016-07-22 16:37:44 -03:00
spi spi: spidev_test: Fix typo in error message 2015-12-08 17:58:56 +00:00
testing Merge branch 'next' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2016-07-29 17:38:46 -07:00
thermal/tmon tools/thermal: tmon: use pkg-config also for CFLAGS 2015-10-10 11:32:31 +08:00
time
usb usbip: adding names db to port operation 2016-05-03 14:32:07 -07:00
virtio ptr_ring: support resizing multiple queues 2016-07-01 05:32:17 -04:00
vm tools/vm/page_owner: increase temporary buffer size 2016-07-26 16:19:19 -07:00
Makefile tools/gpio: add install section 2016-06-23 11:07:13 +02:00