Re: [Qemu-devel] [PATCH] linux-user: Support explicit targets for PowerPC

[Aaron Sierra <asierra@xes-inc.com>]

----- Original Message -----
> From: "Laurent Vivier" <laurent@vivier.eu>
> Sent: Tuesday, November 7, 2017 9:27:38 AM

> Le 07/11/2017 à 16:20, Aaron Sierra a écrit :
>> ----- Original Message -----
>>> From: "Laurent Vivier" <laurent@vivier.eu>
>>> Sent: Tuesday, November 7, 2017 3:24:52 AM
>> 
>>> Le 07/11/2017 à 03:50, Aaron Sierra a écrit :
>>>> Enable building PowerPC targets supporting a specific CPU, without
>>>> having to set QEMU_CPU via the environment. For example these build
>>>> targets (and many more) become available:
>>>>
>>>> qemu-ppc.e500mc qemu-ppc.e500v2 qemu-ppc.e5500 qemu-ppc.e600
>>>> qemu-ppc.e6500
>>>>
>>>> These (statically compiled) binaries have proven useful for
>>>> emulating PowerPC CPUs within Docker containers, where it's hard to
>>>> reliably define environment variables that are available for every
>>>> process.
>>>>
>>>
>>> An other idea would be to extract the default cpu from argv[0].
>>>
>>> We don't change the default CPU at compile time, but we check the binary
>>> name:
>>> - if it's qemu-ppc, let's use the default cpu for qemu-ppc
>>> - if it's not qemu-ppc, but something like qemu-ppc.XXX, let's set the
>>> CPU to XXX. For instance "qemu-ppc.e600" will be a shortcut for
>>> "qemu-ppc -cpu e600". [1]
>>>
>>> I think it's easy to implement and don't change the default behavior of
>>> qemu. And you can use hardlink to define several binaries with different
>>> defaults (like busybox)
>> 
>> Laurent,
>> 
>> I had that thought, too, as being the cleanest and simplest to implement,
>> but it didn't work out as a practical solution. Having execution depend
>> on the name of the file would require a lot of tuning of magics, masks,
>> and interpreters in /proc/sys/fs/binfmt_misc to get the behavior that I
>> depend on. It would require one entry per binary.
>> 
>> With the implementation that I've proposed, I only need two fairly generic
>> entries (ppc and ppc64) stock from Ubuntu's qemu-user-static package.
>> With Docker it's trivial to bind <any_path>/qemu-ppc.e500mc to
>> /usr/bin/qemu-ppc-static within the container. Which gives me complete
>> control over how the container is emulated.
> 
> So I (sadly) think the wrapper is the best solution...
> 
> write a C statically linked program that call the qemu-user-static with
> the good "-cpu" value.
> 
> Something like:
> 
> https://github.com/parazyd/qemu-wrapper/blob/master/qemu-wrapper.c

Laurent,

Yes, that seems like a very simple solution to my problem. Thanks for
the tip. I'll give it a shot.

-Aaron S.

> 
> Laurent