syscall: add support to get pidfd from ForkExec on Linux
Add PidFD support, so that if the PidFD pointer in SysProcAttr is not
nil, ForkExec (and thus all its users) obtains a pidfd from the kernel
during clone(), and writes the result (or -1, if the functionality
is not supported by the kernel) into *PidFD.
The functionality to get pidfd is implemented for both clone3 and clone.
For the latter, an extra argument to rawVforkSyscall is needed, thus the
change in asm files.
Add a trivial test case checking the obtained pidfd can be used to send
a signal to a process, using pidfd_send_signal. To test clone3 code path,
add a flag available to tests only.
Updates #51246.
Change-Id: I2212b69e1a657163c31b4a6245b076bc495777a3
Reviewed-on: https://go-review.googlesource.com/c/go/+/520266
Auto-Submit: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Kirill Kolyshkin <kolyshkin@gmail.com>