Re: [Qemu-discuss] signal SIGILL, Illegal instruction for "mtc0 zero, c0_cause"

[Peter Maydell]

On 14 April 2017 at 08:31, Zhangwen (Esan) <address@hidden> wrote:
> Hi,
>   When I run a binary with qemu-2.7.1, I found it report a error:
> Program received signal SIGILL, Illegal instruction.
>   Then I gdb it, the scene is as follows:
> (gdb) si
>
> Program received signal SIGILL, Illegal instruction.
> _start () at ../newlib-2.2.0/libgloss/mips/crt0.S:92
> 92              nop
> (gdb) disass
> Dump of assembler code for function _start:
> => 0x00000040 <+0>:     mtc0    zero,c0_cause
>    0x00000044 <+4>:     nop
>
> The binary is compiled with newlib-2.2.0, but it works with glibc-2.20.
> "mtc0" instruction can not be recognized by qemu-2.7.1 or any others?
> So I have no idea what happened and could anybody explain the reason?

Are you running a single binary under qemu's user emulation,
or an entire MIPS kernel in qemu's system emulation and some
binary inside that, or are you running this as a bare-metal
binary in system emulation?

If you're just running a single binary with usermode emulation,
I think this is expected -- c0_cause is a system register which
can only be accessed if you're the kernel, and qemu's usermode
emulation runs the guest code as a user process, so SIGILL is the
correct response.

thanks
-- PMM