This does the same as the previous MR, but fixes the issue where the
parent process got the mapping (and at the wrong address) and not the
child process.
Note that this is very preliminary, and I merely got my already freezing
kernel branch not to triple fault, but I would probably apply this patch
to upstream.
What is changed here, is that rather than relying on recursive mapping
for accessing page table frames, it now uses linear translation
(virt=phys+KERNEL_OFFSET). The only problem is that the paging code now
makes assumptions that the entire physical address space remains mapped,
which is not necessarily the case on x86_64 architecturally, even though
systems with RAM more than a PML4 are very rare. We'd probably lazily
(but linearly) map physical address space using huge pages.
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 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.
The cool thing here is that we're temporarily binary compatible with the
old stuff, so if anyone would use an old version of redox_syscall we can
easily find them with these prints.
4lDO2