| Age | Commit message (Collapse) | Author |
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+ 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.
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+ It really only works with Sv39, I suppose similar structures should be
added for Sv4} etc. if I ever get around to it.
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+ Both easier to look at and now the userspace doesn't play as big of a
role in the 'benchmarking' with optimizations turned on.
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+ 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.
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The output is close enough, and I like that uncrustify is a third-party
tool, so people can install a single tool for formatting instead of
having to lug around a whole toolchain. I fully expect to have to add
settings to uncrustify.conf, but let's see how this goes.
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+ Next step, start documenting contents of each file.
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+ Closer to what it's for rather than what it is.
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+ 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.
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lower 8 bits are reserved for arch-specific flags (but at least
read/write/execute) and higher 8 bits are metadata, currently only for
VM_VIRTUAL (to be used when the backing physical memory shouldn't be
freed)
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+ Probably completely unnecessary stylistic thing, but I'll roll with it
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+ Release mode is sort of broken, as lto doesn't work with linker
relaxation and turning the relaxation off causes issues with the jump
from init to kernel (as I've currently implemented it, could probably
be fixed with a manual jump from assembly, I'll add it to my TODO
list)
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