Re: Generic way to detect qemu linux-user emulation

[Andreas Schwab <schwab@suse.de>]

On Mär 18 2025, Daniel P. Berrangé wrote:

> That would get the synchronization behaviour of Linux vfork,
> but I'm not sure it'd get the performance benefits (of avoiding
> page table copying) which is what  Andreas mentioned as the
> desired thing ?

For an emulation performance isn't a thing, what we need is accuracy.
The current issue I have right now is that the MozillaFirefox package
fails to build because posix_spawn behaves unexpectedly.

https://build.opensuse.org/package/live_build_log/openSUSE:Factory:RISCV/MozillaFirefox/standard/riscv64

[  666s]  4:55.15 Traceback (most recent call last):
[  666s]  4:55.16   File "/home/abuild/rpmbuild/BUILD/MozillaFirefox-136.0.1-build/firefox-136.0.1/security/nss/./coreconf/werror.py", line 80, in <module>
[  666s]  4:55.16     main()
[  666s]  4:55.16     ~~~~^^
[  666s]  4:55.16   File "/home/abuild/rpmbuild/BUILD/MozillaFirefox-136.0.1-build/firefox-136.0.1/security/nss/./coreconf/werror.py", line 10, in main
[  666s]  4:55.16     cc_is_clang = 'clang' in subprocess.check_output(
[  666s]  4:55.16                              ~~~~~~~~~~~~~~~~~~~~~~~^
[  666s]  4:55.16       [cc, '--version'], universal_newlines=True, stderr=sink)
[  666s]  4:55.16       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[  666s]  4:55.16   File "/usr/lib64/python3.13/subprocess.py", line 474, in check_output
[  666s]  4:55.16     return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
[  666s]  4:55.16            ~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[  666s]  4:55.17                **kwargs).stdout
[  666s]  4:55.17                ^^^^^^^^^
[  666s]  4:55.17   File "/usr/lib64/python3.13/subprocess.py", line 579, in run
[  666s]  4:55.17     raise CalledProcessError(retcode, process.args,
[  666s]  4:55.17                              output=stdout, stderr=stderr)
[  666s]  4:55.17 subprocess.CalledProcessError: Command '['/usr/bin/ccache /usr/bin/gcc', '--version']' returned non-zero exit status 127.

A real posix_spawn would have set errno to ENOENT.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."