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>
4a084ecfc8