linux_dsm_epyc7002/tools/perf/arch
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
..
alpha perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
arm perf unwind: Separate local/remote libunwind config 2016-06-07 12:08:52 -03:00
arm64 perf callchain: Support aarch64 cross-platform 2016-06-07 15:13:35 -03:00
mips perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
parisc perf tools: Add empty Build files for architectures lacking them 2015-08-06 16:24:15 -03:00
powerpc perf probe ppc64le: Fix probe location when using DWARF 2016-08-09 12:14:29 -03:00
s390 perf s390: Fix 'start' address of module's map 2016-07-26 16:46:12 -03:00
sh perf dwarf: Fix potential array out of bounds access 2015-09-01 11:33:48 -03:00
sparc perf dwarf: Fix potential array out of bounds access 2015-09-01 11:33:48 -03:00
x86 libnvdimm for 4.8 2016-07-28 17:38:16 -07:00
xtensa perf tools xtensa: Add DWARF register names 2015-08-06 16:45:05 -03:00
Build perf build: Add arch x86 objects building 2015-02-12 13:12:01 -03:00
common.c perf tools: Remove needless includes from cache.h 2016-07-12 15:19:58 -03:00
common.h perf tools: Export normalize_arch() function 2016-06-07 12:08:53 -03:00