Re: [Qemu-devel] [RFC PATCH] hw/core: expand description of null-machine

["Alex Bennée" <alex.bennee@linaro.org>]

Thomas Huth <thuth@redhat.com> writes:

> On 25.04.2018 17:33, Alex Bennée wrote:
>> People following old instructions for QEMU get the message "No machine
>> specified, and there is no default" and run -machine help to pick a
>> new machine. Lay people might consider the null-machine to be such a
>> basic starting point but they won't get far. This leads to confusion,
>> see https://bugs.launchpad.net/qemu/+bug/1766896 as an example.
>>
>> I'm open to better words - I figured "THIS PROBABLY ISN'T WHAT YOU
>> WANT" seemed less helpful though.
>>
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> ---
>>  hw/core/null-machine.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/core/null-machine.c b/hw/core/null-machine.c
>> index cde4d3eb57..72f0815045 100644
>> --- a/hw/core/null-machine.c
>> +++ b/hw/core/null-machine.c
>> @@ -50,7 +50,7 @@ static void machine_none_init(MachineState *mch)
>>
>>  static void machine_none_machine_init(MachineClass *mc)
>>  {
>> -    mc->desc = "empty machine";
>> +    mc->desc = "empty machine (for probing/QMP)";
>
> Actually, with certain CPUs, you can really use the "none" machine as a
> pure instruction set testing system. For example, on m68k, there used to
> be an explicit "dummy" machine for this job, and we removed it in favour
> of the "none" machine:
>
> https://git.qemu.org/?p=qemu.git;a=commitdiff;h=22f2dbe7eaf3e12e38c9c210

Ahh OK. Do you know what other CPUs can be used in this way?

> So I'd rather not add such wording. We should rather fix those segfaults
> instead (QEMU should never segfault - in case a device can not be used
> with the "none" machine, there rather should be an error message instead).

Hmm the ARM world is complicated by peripherals that are on-chip but not
part of the "CPU". I wonder if this is a edge case for our modelling?
Should for example -cpu cortex-m3 imply additional peripherals and how
do we handle that in the -m none case?

--
Alex Bennée