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v2.6.28 KGDB/GDB problem resolving module function addresses
- From: "Suresh P.C" <suresh dot pc123 at gmail dot com>
- To: gdb at sourceware dot org
- Date: Sat, 19 Sep 2009 11:25:09 +0530
- Subject: v2.6.28 KGDB/GDB problem resolving module function addresses
v2.6.28 of the kernel seems to have changed the way module sections
are created which prevents KGDB/GDB (v6.8) from correctly evaluating
the addresses of functions within the module. The problem does not
exist with kernel v2.6.26. Example follows:
After I load a module, I can see the module section information in the
directory /sys/module/chardev/sections as follows:
#ls -a
. .symtab
.. .text
.bss .text.cleanup_module
.data .text.device_ioctl
.fixup .text.device_open
.gnu.linkonce.this_module .text.device_read
.note.gnu.build-id .text.device_release
.reginfo .text.device_write
.rodata.str1.4 .text.init_module
.strtab __ex_table
#
I then add the module symbols to gdb as follows:
(gdb) add-symbol file chardev.ko 0xc0745000 -s .data 0xc0745e20 -s
.bss 0xc0746000 -s .reginfo 0xc0745534
Now when I try to get the address of a function the wrong value is
returned i.e. all functions get the same address
(gdb) p /x &device_write
$1 = 0xc0745000
(gdb) p /x &device_read
$2 = 0xc0745000
(gdb) p /x &device_open
$3 = 0xc0745000
Tried adding explicitly as follows:
(gdb) add-symbol-file ../moduletest/chardev.ko 0xc0745000 -s .reginfo
0xc0745534 -s .data 0xc0745e20 -s .bss 0xc0746000 -s .text.device_open
0xc07450a0 -s .text.device_write 0xc07450a0 -s .text.device_read
0xc07451ac add symbol table from file "../moduletest/chardev.ko" at
.text_addr = 0xc0745000
.reginfo_addr = 0xc0745534
.data_addr = 0xc0745e20
.bss_addr = 0xc0746000
.text.device_open_addr = 0xc07450a0
.text.device_write_addr = 0xc07450a0
.text.device_read_addr = 0xc07451ac (y or n) y Reading symbols
from /home/suresh/moduletest/chardev.ko...done.
(gdb)
However, the result is still the same i.e.:
(gdb) p /x &device_write
$4 = 0xc0745000
(gdb) p /x &device_read
$5 = 0xc0745000
(gdb) p /x &device_open
$6 = 0xc0745000
Any help/explanation appreciated.
Regards,
Suresh