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After I loaded linux kernel module with
user@c4:$ insmod mmaptest.ko
I can verify that it is loaded via
user@c4:$ cat /proc/modules
mmaptest 12727 0 - Live 0x0000000000000000 (OF)
but all segments are listed with 0x00 addresses.
user@c4$:$ systool -vm mmaptest
Module = "mmaptest"
Attributes:
coresize = "12727"
initsize = "0"
initstate = "live"
refcnt = "0"
srcversion = "EABEF6F90BEAAD0D15B576A"
taint = "OF"
uevent = <store method only>
Parameters:
count = "0"
Sections:
.bss = "0x0000000000000000"
.data = "0x0000000000000000"
.exit.text = "0x0000000000000000"
.gnu.linkonce.this_module= "0x0000000000000000"
.init.text = "0x0000000000000000"
.note.gnu.build-id = "0x0000000000000000"
.rodata = "0x0000000000000000"
.rodata.str1.1 = "0x0000000000000000"
.rodata.str1.8 = "0x0000000000000000"
.smp_locks = "0x0000000000000000"
.strtab = "0x0000000000000000"
.symtab = "0x0000000000000000"
.text = "0x0000000000000000"
__mcount_loc = "0x0000000000000000"
__param = "0x0000000000000000"
Thus when I try to load symbols from module text segment at incorrect (?) addresses I get:
(gdb) add-symbol-file /home/mmaptest/mmaptest.ko 0x00
add symbol table from file "/home/mmaptest/mmaptest.ko" at
.text_addr = 0x0
(y or n) y
Reading symbols from /home/mmaptest/mmaptest.ko...(**no debugging symbols found**)...done.
Is this the case about module itself or loading into kernel code? Why all addresses are 0x000000000000?
784
1 Answer. Show activity on this post. You need CONFIG_DEBUG_INFO=y on the config. More exactly, the question is Compile the kernel with debug info (DEBUG_INFO) [N/y/?] and it's under the Kernel debugging (DEBUG_KERNEL) [Y/n/?]
You need to use modinfo command to display or show information about a Linux Kernel loaded modules. Use the lsmod command to obtain list of loaded modules in the Linux kernel.
Linux. Loadable kernel modules in Linux are loaded (and unloaded) by the modprobe command. They are located in /lib/modules or /usr/lib/modules and have had the extension . ko ("kernel object") since version 2.6 (previous versions used the .o extension).
My flags were incorrect. Debugging symbol table is built with this makefile:
obj-m += mmaptest.o
MY_CFLAGS += -g -DDEBUG
ccflags-y += ${MY_CFLAGS}
CC += ${MY_CFLAGS}
all:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
debug:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
EXTRA_CFLAGS="$(MY_CFLAGS)"
clean: make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
This can be verified now with:
peter@c4:$ readelf -S mmaptest.ko | grep debug
[24] .debug_info PROGBITS 0000000000000000 00000d40
[25] .rela.debug_info RELA 0000000000000000 00018260
[26] .debug_abbrev PROGBITS 0000000000000000 0000d577
[27] .debug_loc PROGBITS 0000000000000000 0000dd54
[28] .rela.debug_loc RELA 0000000000000000 00029510
[29] .debug_aranges PROGBITS 0000000000000000 0000e5d5
[30] .rela.debug_arang RELA 0000000000000000 0002a3e0
[31] .debug_ranges PROGBITS 0000000000000000 0000e645
[32] .rela.debug_range RELA 0000000000000000 0002a458
[33] .debug_line PROGBITS 0000000000000000 0000e815
[34] .rela.debug_line RELA 0000000000000000 0002a878
[35] .debug_str PROGBITS 0000000000000000 0000f4cd
[38] .debug_frame PROGBITS 0000000000000000 00016e80
[39] .rela.debug_frame RELA 0000000000000000 0002a8c0
add symbol table from file "/home/peter/projects/svn/linux_kernel/mmaptest/mmaptest.ko"
at .text_addr = 0x0
(y or n) y
Reading symbols from /home/peter/projects/svn/linux_kernel/mmaptest/mmaptest.ko...done.
(gdb)
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