Re: [Qemu-devel] [PATCH] null-machine: Add support for the "-kernel" parameter

[Thomas Huth]

On 27.02.2017 14:16, Marcel Apfelbaum wrote:
> On 02/27/2017 01:43 PM, Thomas Huth wrote:
>> On 25.01.2017 09:40, Thomas Huth wrote:
>>> We can have basic support for the "-kernel" parameter quite easily
>>> by using the generic loader device. This should be enough for most
>>> boards which do not need special machine-specific magic for loading
>>> a kernel (and for those that need special magic, the generic "none"
>>> machine is likely not suitable for using it as an instruction set
>>> simulator board anyway).
>>>
>>> Signed-off-by: Thomas Huth <address@hidden>
>>> ---
>>>  PS: If we can't agree on using the generic loader here, I can also
>>>      prepare a patch instead that simply prints out an error message
>>>      if the user tried to use the "-kernel" parameter.
>>>
>>>  hw/core/null-machine.c | 14 ++++++++++++++
>>>  1 file changed, 14 insertions(+)
>>>
>>> diff --git a/hw/core/null-machine.c b/hw/core/null-machine.c
>>> index 27c8369..866e699 100644
>>> --- a/hw/core/null-machine.c
>>> +++ b/hw/core/null-machine.c
>>> @@ -5,6 +5,7 @@
>>>   *
>>>   * Authors:
>>>   *  Anthony Liguori   <address@hidden>
>>> + *  Thomas Huth       <address@hidden>
>>>   *
>>>   * This work is licensed under the terms of the GNU GPL, version 2
>>> or later.
>>>   * See the COPYING file in the top-level directory.
>>> @@ -16,6 +17,7 @@
>>>  #include "qemu/error-report.h"
>>>  #include "hw/hw.h"
>>>  #include "hw/boards.h"
>>> +#include "hw/core/generic-loader.h"
>>>  #include "sysemu/sysemu.h"
>>>  #include "exec/address-spaces.h"
>>>  #include "cpu.h"
>>> @@ -40,6 +42,18 @@ static void machine_none_init(MachineState *mch)
>>>          memory_region_allocate_system_memory(ram, NULL, "ram",
>>> mch->ram_size);
>>>          memory_region_add_subregion(get_system_memory(), 0, ram);
>>>      }
>>> +
>>> +    /* Load kernel */
>>> +    if (mch->kernel_filename) {
>>> +        DeviceState *loader;
>>> +
>>> +        loader = qdev_create(sysbus_get_default(),
>>> TYPE_GENERIC_LOADER);
>>> +        qdev_prop_set_string(loader, "file", mch->kernel_filename);
>>> +        if (cpu) {
>>> +            qdev_prop_set_uint32(loader, "cpu-num", cpu->cpu_index);
>>> +        }
>>> +        qdev_init_nofail(loader);
>>> +    }
>>>  }
>>>
>>>  static void machine_none_machine_init(MachineClass *mc)
>>
>> *ping*
>>
>> Apparently the discussion has ceased ... can we get a consensus whether
>> we want to support the "-kernel" parameter for the "none" machine or not?
>>
> 
> Why do we need the "-kernel" parameter for the null-machine? I mean -
> what are the use cases?

Since it is now possible to instantiate a CPU and memory with the
null-machine, you can use it as a simple instruction set simulator board
now. Start QEMU with something like "-M none -cpu xxx -m 1G -S -s" and
then connect a remote GDB to interact with the emulated CPU. This is
e.g. useful for CPU models that do not have a matching emulated machine
yet. Adding the possibility to use the "-kernel" parameter for this,
too, would make things a little bit more comfortable on certain targets,
since you then don't have to fiddle with the generic-loader device.

 Thomas