Re: [Qemu-devel] [PATCH] hw/core/null-machine: Add the possibility to instantiate a CPU, RAM and kernel

[Laurent Vivier]

Le 14/01/2017 à 07:51, Thomas Huth a écrit :
> Sometimes it is useful to have just a machine with CPU and RAM, without
> any further hardware in it, e.g. if you just want to do some instruction
> debugging for TCG with a remote GDB attached to QEMU, or run some embedded
> code with the "-semihosting" QEMU parameter. qemu-system-m68k already
> features a "dummy" machine, and xtensa a "sim" machine for exactly this
> purpose.
> All target architectures have nowadays also a "none" machine, which would
> be a perfect match for this, too - but it currently does not allow to add
> CPU, RAM or a kernel yet. Thus let's add these possibilities in a generic
> way to the "none" machine, too, so that we hopefully do not need additional
> "dummy" machines in the future anymore (and maybe can also get rid of the
> already existing "dummy"/"sim" machines one day).
> Note that the default behaviour of the "none" machine is not changed, i.e.
> no CPU and no RAM is instantiated by default. You've explicitely got to
> specify the CPU model with "-cpu" and the amount of RAM with "-m" to get
> these new features.

Did you try to use the generic-loader to load the kernel?

Something like "-device loader,file=vmlinux" instead of adding this part
in the none machine?

Perhaps we could also add a cpu this way, as they are already available
in the device list for the machine that allows hotplug.

With the same idea, we could also have a "-device ram,size=XXX" to add
ram (not DIMM).

I think is is the idea behind the none machine:

commit b4a738bf93c3137b92d532e59d60edccc4e1ea96
Author: Anthony Liguori <address@hidden>
Date:   Wed Aug 22 15:22:05 2012 -0500

    boards: add a 'none' machine type to all platforms

    This allows any QEMU binary to be executed with:

      $QEMU_BINARY -M none -qmp stdio

    Without errors from missing options that are required by various
boards.  This
    also provides a mode that we can use in the future to construct machines
    entirely through QMP commands.

Laurent