According to Agner Fog's documentation
(https://agner.org/optimize/instruction_tables.pdf), the following information
is true:
These instructions have identical latency and throughput, except for Zen
5, which lists `test` as having reciprocal throughput of 0.25 cycles,
and `bt` having reciprocal throughput of 0.33 cycles. This rules out the
`bt` instruction for being the ideal instruction.
The other `test` instructions were removed as candidates because,
regardless of the size of the memory fetched at the address, at least 64
bytes will need to be fetched because it will be stored in the cache
line. The WORD and DWORD cases can be ruled out because we cannot assume
that `rsp + 16` or `rsp + 17` will not be on a 64-byte alignment
boundary, which would cause two cachelines to be essentially filled with
garbage we don't care about. The best case scenario is that we only need
to fill one cache line with garbage, which is what the BYTE version does
every time.
This only adds a pointer worth of overhead per cpu core in the
PerCpuBlock struct.
Also fix a bunch of unsafe_op_in_unsafe_fn warnings in the profiling
code.
This way we can choose our own size for the stack and don't have to
identity map it manually. Also this way the bootloader doesn't have to
change the stack pointer right before calling into the kernel (which it
currently does in an unsound way)
Inspired by how Haiku does printing for its kernel debugger, this commit
gets rid of the scrolling when the bootlog reaches the end of the screen
and instead wraps around to the start of the screen. Between the last
written line and the first visible written line there is always a blank
line to provide visual separation.
Getting rid of the scrolling significantly simplifies the implementation
of graphical debug and removes the need for double buffering for
performance as we no longer need to read back the framebuffer when
scrolling which is very expensive on write-combining memory like the
framebuffer.
This significantly reduces the amount of boot logs produced by the
kernel by default on x86. With this the full kernel boot logs now fit on
a single screen on my system.
This allows them to be immediately installed by kstart/kstart_ap without
having to wait for the page tables to be set up correctly. This removes
the initial IDT.
bjorn3