Re: Generic way to detect qemu linux-user emulation

[Helge Deller <deller@gmx.de>]

On 3/18/25 11:36, Helge Deller wrote:
> On 3/18/25 11:18, Andreas Schwab wrote:
>> Is there a generic way for a program to detect that is it being run
>> inside the linux-user emulation?
>
> Yes, having a reliable way to detect it would be good.

In qemu-user emulation we could change the return values of
"uname --processor" and/or "uname --hardware-platform".
Currently both always return "unknown", but in qemu we could
return the arch of the host.

Another possibility is to extend prctl(), but I think uname is
easier to handle in scripts and such...


> My current (unreliable) way to detect it is using uname.
> The kernel string and arch name don't match:
>
> (sid_hppa)root@paq:/# uname -a
> Linux paq 6.1.0-31-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.128-1 (2025-02-07) parisc GNU/Linux
>
> (sid_hppa)root@paq:/# uname -r
> 6.1.0-31-amd64
>
> (sid_hppa)root@paq:/# uname -m
> parisc
>
> This is a qemu-linux-user parisc(hppa) emulation running on x86-64.
>
>> The purpose for that would be to work around limitations of the
>> emulation, like CLONE_VFORK being unsupported.
>
> yes, and robust futexes aren't supported either.
>
>>  For example, python >=
>> 3.13 needs to avoid using posix_spawn in that case, because the
>> emulation of CLONE_VFORK as a true fork makes it impossible for it to
>> report errors back to the parent process.