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

[Eduardo Habkost]

On Mon, Jan 16, 2017 at 10:53:07AM -0800, Alistair Francis wrote:
> On Sun, Jan 15, 2017 at 11:59 PM, Thomas Huth <address@hidden> wrote:
> > On 14.01.2017 12:03, Laurent Vivier wrote:
> >> 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?
> >
> > It does not work by default - because we need a way to set the CPU's
> > program counter to the entry point of the ELF file.
> 
> The -device loader logic can set the PC to the entry point of the ELF.
> You just need to specify 'cpu-num=x' when loading the file.
> 
> > But I think the users also expect the "-kernel" parameter to be working,
> > so I think we should add the loader code in null-machine.c anyway.
> 
> I agree that uses probably expect the '-kernel' option to work as well.

So, is it possible to write a generic load_kernel() function that
simply reuses the generic-loader code?

-- 
Eduardo