Some of system registers are inaccessible via GDB if CPU is in UserMode

[kokas-a]

Hi colleagues,
I found unclear behavior of QEMU while debugging Zephyr. While CPU is in UserSpace mode (STATUS32 & (1 << 7) ==1) it's impossible to get system registers values because of QEMU falls with error:

**
ERROR:../qemu/accel/tcg/cpu-exec.c:933:cpu_exec: assertion failed: (cpu == current_cpu)
Bail out! ERROR:../qemu/accel/tcg/cpu-exec.c:933:cpu_exec: assertion failed: (cpu == current_cpu)

How to reproduce

Build Zephyr with default GCC-compiler (or download prepared elf-example):

west build -b qemu_arc_hs samples/userspace/hello_world_user/

Start recent version of qemu (https://github.com/foss-for-synopsys-dwc-arc-processors/qemu):

qemu-system-arc -cpu archs -m 8M -nographic -no-reboot -monitor none -global cpu.firq=false -global cpu.num-irqlevels=15 -global cpu.num-irq=25 -global cpu.ext-irq=20 -global cpu.freq_hz=10000000 -global cpu.timer0=true -global cpu.timer1=true -global cpu.has-mpu=true -global cpu.mpu-numreg=16 -net none -pidfile qemu.pid -chardev stdio,id=con,mux=on -serial chardev:con -mon chardev=con,mode=readline -icount shift=6,align=off,sleep=off -rtc clock=vm -kernel <PATH_TO_ZEPHYR_USER_ELF> -s -S

Attach GDB:

target remote :1234
file <PATH_TO_ZEPHYR_USER_ELF>
b user_function
continue
info registers

Get GDB output:

timer_build    0x304               [ version=4 t0 t1 p0=0 p1=0 ]
irq_build      0xf141901           [ version=1 IRQs=25 exts=20 p=15 ]
mpy_build      0x1006              [ version32x32=6 type=0 cyc=0 DSP=1 version16x16=0 ]
vecbase_build  0x10                [ version=4 addr=0 ]
--Type <RET> for more, q to quit, c to continue without paging--
isa_config     0x12e47402          [ version=2 pc_size=4 lpc_size=7 addr_size=4 a n l c=2 d=1 ]
Remote connection closed

Get QEMU output:

**
ERROR:../qemu/accel/tcg/cpu-exec.c:933:cpu_exec: assertion failed: (cpu == current_cpu)
Bail out! ERROR:../qemu/accel/tcg/cpu-exec.c:933:cpu_exec: assertion failed: (cpu == current_cpu)

zephyr_user.zip