Re: [9fans] 386

[Russ Cox <rsc@swtch.com>]

On reflection it's just not that hard to write a C invlpg
that calls putcr3 if it's running on a 386.  We use
LOCK INCL to do ref counts so that it works on the 386,
we never use BSWAP, and we use CR0.WP by checking
the cpuid.

For actually running a system, VMware and Qemu are
pretty much neck and neck and Bochs is far behind.

For debugging a system, Bochs is slightly ahead of
Qemu and VMware is far behind.  Bochs has a reasonable
debugger interface that knows about 16-bit mode and
segments and offsets and page tables and everything.
Qemu is much faster but has no debugger.  You can attach
to it with gdb but gdb only knows about 32-bit mode user-level
sorts of things, so usually I have to set a break point using gdb
and then dump register info back at qemu's console.
I lost count of the number of times one or the other got me out
of a jam while I was writing the new VM code or the realmode
code that made vesa-in-the-kernel possible.

Russ