The 'perf report' tool does not display the addresses of kernel module
symbols correctly.

For example symbol qeth_send_ipa_cmd in kernel module qeth.ko has this
relative address for function qeth_send_ipa_cmd():

  [root@s8360047 linux]# nm -g drivers/s390/net/qeth.ko | fgrep send_ipa_cmd
  0000000000013088 T qeth_send_ipa_cmd

The module is loaded at address:

  [root@s8360047 linux]# cat /sys/module/qeth/sections/.text
  0x000003ff80296d20
  [root@s8360047 linux]#

This should result in a start address of:

  0x13088 + 0x3ff80296d20 = 0x3ff802a9da8

Using crash to verify the address on a live system:

  [root@s8360046 linux]# crash vmlinux

  crash 7.1.9++
  Copyright (C) 2002-2016  Red Hat, Inc.
  Copyright (C) 2004, 2005, 2006, 2010  IBM Corporation

  [...]

  crash> mod -s qeth drivers/s390/net/qeth.ko
       MODULE       NAME        SIZE  OBJECT FILE
       3ff8028d700  qeth      151552  drivers/s390/net/qeth.ko
  crash> sym qeth_send_ipa_cmd
  3ff802a9da8 (T) qeth_send_ipa_cmd [qeth] /root/linux/drivers/s390/net/qeth_core_main.c: 2944
  crash>

Now perf report displays the address of symbol qeth_send_ipa_cmd:
symbol__new:

  qeth_send_ipa_cmd 0x130f0-0x132ce

There is a difference of 0x68 between the entry in the symbol table (see
nm command above) and perf. The difference is from the offset the .text
segment of qeth.ko:

  [root@s8360047 perf]# readelf -a drivers/s390/net/qeth.ko
  Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .note.gnu.build-i NOTE             0000000000000000  00000040
       0000000000000024  0000000000000000   A       0     0     4
  [ 2] .text             PROGBITS         0000000000000000  00000068
       000000000001c8a0  0000000000000000  AX       0     0     8

As seen the .text segment has an offset of 0x68 with start address 0x0.
Therefore 0x68 is added to the address of qeth_send_ipa_cmd and thus
0x13088 + 0x68 = 0x130f0 is displayed.

This is wrong, perf report needs to display the start address of symbol
qeth_send_ipa_cmd at 0x13088 + qeth.ko.text section start address.

The qeth.ko module .text start address is available in the qeth.ko DSO
map. Just identify the kernel module symbols and correct the addresses.

With the fix I see this correct address for symbol: symbol__new:
qeth_send_ipa_cmd 0x3ff802a9da8-0x3ff802a9f86

Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Reviewed-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Zvonko Kosic <zvonko.kosic@de.ibm.com>
LPU-Reference: 20170803134902.47207-1-tmricht@linux.vnet.ibm.com
Link: http://lkml.kernel.org/n/tip-q8lktlpoxb5e3dj52u1s1rw4@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>