We may also want to do this with the MADT and the HPET tables, and let
user drivers specify what the tables mean independent of ACPI. That is,
adding an interface for registering new CPUs, and specifying the main
timer IRQ.
Currently, there are some things that need to be set up by userspace
that the kernel previously did. These include telling firmware when the
I/O APIC is used, and most importantly, shutting down the system.
The former is not particularly important, but for the latter I think
that we could implement this using a "shutdown pipe". Essentially it
will be a file that triggers an event shutting down, which would be used
to notify to acpid that the kernel is requesting a shutdown.
This allows schemes to avoid checking the length against zero before
constructing a slice from pointer+len that the kernel gave.
Additionally, the address is now non-canonical on x86, meaning that
userspace will fail instead of continuing with UB, if they would ever
forget to check the length.
This is done by making sure that when empty() is called on a context,
the grants Arc will be replaced with a new unused Arc, hence
decrementing the refcount. Previously this was only done when the
context was actually reaped, but since there is no guarantee as far as I
am aware about when this must happen, the grants could be completely
leaked, leading to the error.
This allows schemes to avoid checking the length against zero before
constructing a slice from pointer+len that the kernel gave.
Additionally, the address is now non-canonical on x86, meaning that
userspace will fail instead of continuing with UB, if they would ever
forget to check the length.
Previously, the kernel used the regular FS segment for Thread-Local
Storage. The problem however, is that userspace code also uses FS for
TLS, meaning that the kernel would have to switch the FS segment between
user and kernel, _upon every syscall_. This is obviously suboptimal for
performance (especially with fast syscalls such as futex, nanosleep, or
yield).
I had to search LLVM for hours, just to find out that the insertion of
the memory load with FS was actually done in the linker, so I added a
flag for that.
I haven't done any proper benchmarking, but the boot process seems to
have gotten much faster!
4lDO2