This reverts commit 8f04deadc1f1620dbd0aaea07f04a6c7f82f58c0.
The actual issue was triggered by a memory corruption due to the fact
that the exception handling gate code did not preserve XMM regs.
The bug manifested itself as a series of null bytes appearing to the
tty device when the ring buffer gets linked to it and its contents are
flushed to the tty.
Using gdb, I was able to track the problem into the ringbuf's Read
method and specifically to the call to copy(). I have replaced the call
with a for loop that the compiler would anyway optimize into a rep stosb
or equivalent asm instruction.
The implementation of Printf has been moved from the early package to
the kfmt package. The dependency to ActiveTerminal has been removed and
the code now uses an io.Writer for its output. As Go interfaces cannot
be used before bootstrapping the Go runtime, the code uses a ring-buffer
fallback for storing any kernel output emitted before that point.
The ring-buffer implements both io.Reader and io.Writer and uses a fixed
size of 2048 bytes (set by the ringBufferSize constant). This provides
enough space to hold a standard 80x25 screen's output.
By setting up pwd as a Go workspace, we can trim import paths from
something like "github.com/achilleasa/gopher-os/kernel" to just
"kernel".
These changes make forking easier and also allows us to move the code to
a different git hosting provider without having to rewrite the imports.
