Kernel debugging - gdb step jumps out of function

Question

I'm trying to do understand the kernel network stack for a security research for my university. That's why I try to debug the linux kernel.

So far I'm doing quite well but I ran in a problem when trying to use qemu and gdb for debugging.

The problem is as follows:

I boot my linux system: make boot

   boot:
        @qemu-system-x86_64 \
            -kernel ${KERNEL_IMAGE} \
            -drive file=${DRIVE_IMAGE},index=0,media=disk,format=raw \
            -append "root=/dev/sda rw console=ttyS0 nokaslr gdbwait" \
            -m ${RAM} \
            --nographic \
            --enable-kvm  \
            -s

And connect with gdb: make debug

debug:
    @gdb -iex "target remote localhost:1234" ${KERNEL_DIRECTORY}/vmlinux

I set a breakpoint e.g. at icmp_rcv and continue

b icmp_rcv
Breakpoint 1 at 0xffffffff81808910: file net/ipv4/icmp.c, line 989.
c

Know I ping myself -> breakpoint hit:

Breakpoint 1, icmp_rcv (skb=0xffff88007c24ee00) at net/ipv4/icmp.c:989

Great so far everything worked as expected. Know I press n/s (next or step) and instead of net/ipv4/icmp.c:990 It says:

native_apic_mem_write (reg=896, v=52414) at ./arch/x86/include/asm/apic.h:99

Know I press n until I come back to icmp_rcv:989. I tried to set a breakpoint to icmp_rcv_990 but gdb never stops there. Has anybody an idea how to fix this?

Thank you!

Yours

MisterPresident · Accepted Answer · 2017-09-11 14:53:38Z

2

Honestly I have no glue why but removing --enable-kvm from my Makefile helped to get it working. I hope this helps other people.

answered Sep 11, 2017 at 14:53

MisterPresident

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1 Comment

Benny Over a year ago

I still have the problem, on a similar file, IGMP.c; Did you found something other helpful?

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