STINNER Victor <vstin...@redhat.com> added the comment:
> Another problem with posix_spawn() on glibc: it doesn't report errors to the
> parent process when run under QEMU user-space emulation and Windows Subsystem
> for Linux. This is because starting with commit [1] (glibc 2.25)
> posix_spawn() relies on address space sharing semantics of clone(CLONE_VM)
> to report errors, but it's not implemented in QEMU and WSL, so
> clone(CLONE_VM) and vfork() behave like fork(). See also [2], [3].
Oh, you know a lot of stuff about vfork and posix_spawn, you are impressive :-)
Is sys.platform equal to 'linux' on WSL? Sorry, I don't know WSL. If it's
equal, is it possible to explicitly exclude WSL in the subprocess test,
_use_posix_spawn()?
For QEMU, I was very surprised that a full VM wouldn't implement vfork. So I
tried Fedora Rawhide and I didn't notice the bug that you described.
---
$ cat test.c
#include <spawn.h>
int main(int argc, char *argv[], char *envp[]) {
return posix_spawn(0, "non-existing", 0, 0, argv, envp);
}
$ gcc test.c
$ ./a.out
$ echo $?
2
---
In the VM, I get exit status 2 as expected.
You wrote:
---
$ aarch64-linux-gnu-gcc -static test.c
$ qemu-aarch64 ./a.out
$ echo $?
0
---
So the bug only affects "QEMU User Space". I never used that before. I
understand that it's a bug in the glibc and in "QEMU User Emulation" which
doesn't implement vfork "properly".
> There is no problem with musl (it doesn't rely on address space sharing).
I'm not interested to support musl at this point because I don't see any
obvious way to detect that we are running musl nor get the musl version.
The history of this issue shows the posix_spawn() only works in some very
specific cases, so we have to be careful and only opt-in for specific libc, on
specific platform with specific libc version (read at runtime if possible).
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<https://bugs.python.org/issue35537>
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