Re: [Qemu-devel] [PATCH] RFC: linux-user-i386: crash on cpuid

[Eduardo Habkost]

On Fri, Sep 16, 2016 at 06:41:32PM +0400, Marc-André Lureau wrote:
> Running cpuid instructions with a simple run like:
> i386-linux-user/qemu-i386 tests/tcg/sha1-i386
> 
> Results in the following assert:
>  #0  0x00007ffff64246f5 in raise () from /lib64/libc.so.6
>  #1  0x00007ffff64262fa in abort () from /lib64/libc.so.6
>  #2  0x00007ffff7937ec5 in g_assertion_message () from /lib64/libglib-2.0.so.0
>  #3  0x00007ffff7937f5a in g_assertion_message_expr () from 
> /lib64/libglib-2.0.so.0
>  #4  0x000055555561b54c in apicid_bitwidth_for_count (count=0) at 
> /home/elmarco/src/qemu/include/hw/i386/topology.h:58
>  #5  0x000055555561b58a in apicid_smt_width (nr_cores=0, nr_threads=0) at 
> /home/elmarco/src/qemu/include/hw/i386/topology.h:67
>  #6  0x000055555561b5c3 in apicid_core_offset (nr_cores=0, nr_threads=0) at 
> /home/elmarco/src/qemu/include/hw/i386/topology.h:82
>  #7  0x000055555561b5e3 in apicid_pkg_offset (nr_cores=0, nr_threads=0) at 
> /home/elmarco/src/qemu/include/hw/i386/topology.h:89
>  #8  0x000055555561dd86 in cpu_x86_cpuid (env=0x555557999550, index=4, 
> count=3, eax=0x7fffffffcae8, ebx=0x7fffffffcaec, ecx=0x7fffffffcaf0, 
> edx=0x7fffffffcaf4) at /home/elmarco/src/qemu/target-i386/cpu.c:2405
>  #9  0x0000555555638e8e in helper_cpuid (env=0x555557999550) at 
> /home/elmarco/src/qemu/target-i386/misc_helper.c:106
>  #10 0x000055555599dc5e in static_code_gen_buffer ()
>  #11 0x00005555555952f8 in cpu_tb_exec (cpu=0x5555579912d0, 
> itb=0x7ffff4371ab0) at /home/elmarco/src/qemu/cpu-exec.c:166
>  #12 0x0000555555595c8e in cpu_loop_exec_tb (cpu=0x5555579912d0, 
> tb=0x7ffff4371ab0, last_tb=0x7fffffffd088, tb_exit=0x7fffffffd084, 
> sc=0x7fffffffd0a0) at /home/elmarco/src/qemu/cpu-exec.c:517
>  #13 0x0000555555595e50 in cpu_exec (cpu=0x5555579912d0) at 
> /home/elmarco/src/qemu/cpu-exec.c:612
>  #14 0x00005555555c065b in cpu_loop (env=0x555557999550) at 
> /home/elmarco/src/qemu/linux-user/main.c:297
>  #15 0x00005555555c25b2 in main (argc=2, argv=0x7fffffffd848, 
> envp=0x7fffffffd860) at /home/elmarco/src/qemu/linux-user/main.c:4803
> 
> The fields are set in qemu_init_vcpu() with softmmu, but it's a stub
> with linux-user.
> 
> Signed-off-by: Marc-André Lureau <address@hidden>
> ---
>  target-i386/cpu.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index 5a5299a..ce8f798 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -3097,7 +3097,10 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
> **errp)
>  
>      mce_init(cpu);
>  
> -#ifndef CONFIG_USER_ONLY
> +#ifdef CONFIG_USER_ONLY
> +    cs->nr_cores = smp_cores;
> +    cs->nr_threads = smp_threads;
> +#else

On CONFIG_USER_ONLY, smp_cores and smp_threads are defined as:

  /* *-user doesn't have configurable SMP topology */
  #define smp_cores   1
  #define smp_threads 1

It sounds simpler to just set nr_cores and nr_threads to 1 by
default in cpu_common_initfn(). (Preferably with a comment noting
that the default value is changed by qemu_init_vcpu() for
softmmu).

-- 
Eduardo