Re: [Qemu-devel] [PATCH v3] hw/core/null-machine: Add the possibility to instantiate a CPU and RAM

[Thomas Huth]

On 18.01.2017 18:57, Alistair Francis wrote:
> On Wed, Jan 18, 2017 at 4:44 AM, Thomas Huth <address@hidden> wrote:
>> 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 and RAM 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 have explicitely got to
>> specify the CPU model with "-cpu" and the amount of RAM with "-m" to get
>> these new features.
>>
>> Signed-off-by: Thomas Huth <address@hidden>
>> ---
>>  v3:
>>  - Get rid of the cpu_init_def() wrapper again, make null-machine.o
>>    target dependent instead and use cpu_init() directly.
>>  - Omit the loader code for the "-kernel" option for now (users can
>>    use "-device loader,..." instead). We can add code for the -kernel
>>    parameter later (either an implementation or a warning), once we've
>>    decided how it should behave for the "none" machine.
> 
> I think there should at least be a warning to start with though. It
> seems confusing that no errors are reported but the argument is
> ignored.

I'm still rather in favor of adding the hunk here that calls the generic
loader for "-kernel" ... anyway, we can add either behavior with a later
patch. So far the "none" machine never reported an error here, so this
is not a regression if we do not have this right from the start.

 Thomas