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On s390x perf test 1 failed. It turned out that commit cf6383f73cf2
("perf report: Fix kernel symbol adjustment for s390x") was incorrect.
The previous implementation in dso__load_sym() is also suitable for
s390x.
Therefore this patch undoes commit cf6383f73cf2
Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Zvonko Kosic <zvonko.kosic@de.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Fixes: cf6383f73cf2 ("perf report: Fix kernel symbol adjustment for s390x")
LPU-Reference: 20170915071404.58398-2-tmricht@linux.vnet.ibm.com
Link: http://lkml.kernel.org/n/tip-v101o8k25vuja2ogosgf15yy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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On s390x perf test 1 failed. It turned out that commit 4a084ecfc821
("perf report: Fix module symbol adjustment for s390x") was incorrect.
The previous implementation in dso__load_sym() is also suitable for
s390x.
Therefore this patch undoes commit 4a084ecfc821.
Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Zvonko Kosic <zvonko.kosic@de.ibm.com>
Fixes: 4a084ecfc821 ("perf report: Fix module symbol adjustment for s390x")
LPU-Reference: 20170915071404.58398-1-tmricht@linux.vnet.ibm.com
Link: http://lkml.kernel.org/n/tip-5ani7ly57zji7s0hmzkx416l@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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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>
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On s390x the kernel text segment starts at address 0x0. When perf
report reads kernel symbols from vmlinux file it adds an offset of
0x1000.
For example see symbol set_reset_devices:
[root@s8360047 linux-devel]# nm -A vmlinux| fgrep set_reset_devices
vmlinux:0000000001379000 t set_reset_devices
[root@s8360047 linux-devel]#
[root@s8360047 linux-devel]# fgrep set_reset_devices /proc/kallsyms
0000000001379000 t set_reset_devices
[root@s8360047 linux-devel]#
The kernel symbol table and the vmlinux file have the same address for
symbol set_reset_devices namely 1379000.
When perf report reads this symbols it displays it with address
symbol__new: set_reset_devices 0x137a000-0x137a018
There is a difference between perf report and vmlinux of 0x1000.
The reason for the difference is at kernel symbol load time in function
dso__load_sym(). The vmlinux file is investigated with its ELF header.
Command readelf shows this:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .text PROGBITS 0000000000000000 00001000
0000000000b0e0c2 0000000000000000 AX 0 0 128
This leads to an invalid calculation of the symbol start address, see
file utit/symbol-elf.c line 974:
/* Adjust symbol to map to file offset */
if (adjust_kernel_syms)
sym.st_value -= shdr.sh_addr - shdr.sh_offset;
With shdr.sh_addr set to 0x0 and shdr.sh_offset set to 0x1000 as read
from the ELF .text section 0x1000 is added to the symbol address.
I would like to fix this by introducing an archticture specific function
named elf__needs_adjust_symbols(). This is the same approach as done by
PowerPC. The function currently does not exist for s390x and the
default weak one is used. The s390x specific one returns false when
symsrc_init() is invoked for kernel symbols and results in variable
adjust_kernel_syms being false. This omits the adjustment and the
correct address is displayed (when symbol resolvement does not work).
The s390x specific function returns false for kernel symbol adjustment
and returns true for kernel modules, processes and shared libraries.
Signed-off-by: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
Cc: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Thomas-Mich Richter <tmricht@linux.vnet.ibm.com>
LPU-Reference: 20170713130252.6167-1-tmricht@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
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