Re: Building QEMU as a Shared Library

[Pierrick Bouvier <pierrick.bouvier@linaro.org>]

Hi Saanjh,

here is a minimal patch that builds one shared library per target (arch, 
mode) where arch is cpu arch, and mode is system or user, and launch 
system-aarch64 through a simple driver:

https://github.com/pbo-linaro/qemu/commit/fbb39cc64f77d4bf1e5e50795c75b62735bf5c5f

With this, it could be possible to create a driver that can execute any 
existing target. It's a sort of single binary for QEMU, but shared 
objects are mandatory, and duplicates all the QEMU state. So there is no 
real benefit compared to having different processes.

In more, to be able to do concurrent emulations, there are much more 
problems to be solved. QEMU state is correctly kept per target, but all 
other libraries states are shared. There are various issues if you 
launch two emulations at the same time in two threads:
- glib global context
- qemu calls exit in many places, which stops the whole process
- probably other things I didn't explore

At this point, even though qemu targets can be built as shared objects, 
I would recommend to use different processes, and implement some form on 
IPC to synchronize all this.
Another possibility is to try to build machines without using the 
existing main, but I'm not sure it's worth all the hassle.

What are you trying to achieve?

Regards,
Pierrick

On 2/24/25 01:10, Philippe Mathieu-Daudé wrote:
> Cc'ing our meson experts
> 
> On 22/2/25 14:36, Saanjh Sengupta wrote:
>> Hi,
>>
>> I referred to your mailing chains on suggesting QEMU to be built as a
>> shared library.
>>
>> *Change meson.build to build QEMU as a shared library (with PIC enabled
>> for static libraries)*
>> *
>> *
>> Could you please suggest what exactly has to be enabled in the meson.build?
>>
>> I am confused on that front.
>>
>> Regards
>> Saanjh Sengupta
>