Cannot insert breakpoint? cannot access memory adresss? need your help!

Hi all,

I have got some trouble when debugging arm64 linux kernel running on QEMU. I connect GDB server built in QEMU and then set breakpoint on particular address. Though data at this address could be examined, neither software breakpoints nor hardware breakpoints could be set. And gdb gives the following message:

Cannot inset breakpoint 1.
Cannot access memory at address 0x40000004

Furthermore, I tried to set hardware breakpoints, it said that “you may have requested too many hardware breakpoints or watchpoints” but actually I did set this one only.

The GDB is the latest one (version 7.11.1) that I compiled on arm64 plaform and the kernel version is v4.4 rc4. Also, I have checked my kernel build configuration
(CONFIG_KGDB=y, 
CONFIG_DEBUG_INFO=y,
CONFIG_DEBUG_BUGVERBOSE=y, 
CONFIG_FRAME_POINTER=y,
CONFIG_KGDB_SERIAL_CONSOLE=y) 
and my compilation argument 
(KBUILD_CFLAGS += -Og). Is there anything I missed? I would appreciate your help in any way.