| Age | Commit message (Collapse) | Author |
|---|
|
|
|
+ User has to 'free' the 0 page before it becomes accessible to mapping.
Probably worth noting that this is likely VERY niche and mainly
concerns stuff like certain kinds of emulators that I'm still
eons from implementing, but still.
Unbacked pages can also be useful for some kinds of notifications,
like 'if someone writes to this page, please report it to me with this
ID' or whatever, I remember seeing some discussion about it somewhere
but that's also not really relevant for the moment.
Most significantly, at least with the current design,
after the null page is freed it becomes available for use to regular req_mem()
calls, so users should probably using locks around memory requests.
That's probably a good idea anyway as internally the kernal has to
lock the virtual memory, and without a scheduler it might cause
threads to spin for a while in the kernel which is rather bad.
|
|
+ Anything extern is right out as LLVM doesn't produce correct code for
them. Maybe if I added some extra attributes but I'm skeptical.
Replaced with static variables and getters/setters.
+ Inline ASM is apparently a bit buggy, so use an assembly stub when jumping to init.
+ Minimize work done in main() to minimize chance of LLVM doing something silly.
Still not 100% certain that I shouldn't just write the main() as an assembly stub
in arch/riscv64 to be absolutely sure everything works as intended.
+ Make .kernel.start section SHF_ALLOC, otherwise lld complains about
pc-relative addressing
Probably some other stuff as well that I'm forgetting right now. But at least with
LLVM14 LTO seems to work, which is pretty cool?
|
|
+ Had some minor issues with a wraparound of size_t that effectively
meant that some regions were allocated twice. Also, booting should be
a bit more reliable now, turned out that the previous iteration of the
booting was just accidentally working due to the kernel being placed
'close enough' in RAM to where it was linked to. Fixed by allocating a
vmem of O1 that maps the kernel to a 2MiB boundary at boot, pretty
nifty.
|
|
|
|
+ The system is now a bit simpler and hopefully easier to understand, while also
extending the shared memory to be 1:N, where there is one owner who
may become a zombie while waiting for the N to die.
|
|
|
|
+ Took some fairly significant changes, for one the kernel is no longer
relocated at the start of a boot, instead it sits wherever the user
decides the kernel should sit. Similarly, the initial kernel stack and
page table are stored within the binary, slightly bloating the size
but making it much safer to boot since there's really no chance of us
overwriting the fdt or initrd in memory.
|
|
+ Make 8250 serial driver more generic
+ Still TODO: write a tutorial on how to boot on the visionfive2
|
|
|
|
|
|
|
|
|
|
|
|
+ The secret is using gravestones. I'll have to write up full
documentation for the feature but essentially riscv lets us encode
whatever we want into page table entries, as long as they're not
active. We use this to encode highest user address that is not a zero,
in that all entries in the top level are either active or gravestones.
When an active entry is removed, it is either a gravestone (if there
are other active entries above it) or it starts a cascade of removing
entries that have been previously removed
Slight runtime overhead to page mapping, pretty major advantage in rpc
calls. Feature will need to be tested more thorougly, and the init
program is sort of a best scenario with just one top level userspace
page table entry active at a time, leading to incredibly fast context
switches.
Current implementation limits a process' max virtual memory to 248 GiB
(in Sv39), but I don't think the missing 8 GiB is that big of a deal.
|
|
|
|
+ In total, a syscall is built up of 6 values, with the first being the
syscall number. Symmetrically, the first value is now a status and the
following five values return "values". This allows us to cram in more
info into the ipc_* functions. The performance difference is
absolutely minimal, at least from my testing in qemu.
|
|
|
|
|
|
|
|
|
|
+ Next step, start documenting contents of each file.
|
|
+ Closer to what it's for rather than what it is.
|
|
|
|
+ next up would probably be to start working on process/thread
relationships, largely as documented. Still not entirely sure about
how I want to handle fork, but I suppose I might figure it out at some
point.
|
|
|
|
|
|
|
|
|
