Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

lib/usys.S

@@ -0,0 +1,110 @@
+#include "syscall.h"
+#include "traps.h"
+
+#define SYSCALL(name) \
+  .global name; \
+  name: \
+    mov $SYS_ ## name, %rax; \
+    mov %rcx, %r10 ;\
+    syscall          ;\
+    ret
+
+SYSCALL(fork)
+.global _xv6_exit
+_xv6_exit:
+    mov $SYS_exit, %rax
+    mov %rcx, %r10
+    syscall
+    ret
+SYSCALL(wait)
+SYSCALL(pipe)
+SYSCALL(read)
+SYSCALL(write)
+SYSCALL(close)
+SYSCALL(kill)
+SYSCALL(exec)
+SYSCALL(open)
+SYSCALL(mknod)
+SYSCALL(unlink)
+SYSCALL(fstat)
+SYSCALL(link)
+SYSCALL(mkdir)
+SYSCALL(chdir)
+SYSCALL(dup)
+SYSCALL(dup2)
+SYSCALL(fcntl)
+SYSCALL(getpid)
+SYSCALL(sbrk)
+SYSCALL(sleep)
+SYSCALL(uptime)
+SYSCALL(vga_sync)
+SYSCALL(getmouse)
+SYSCALL(lseek)
+SYSCALL(reboot)
+SYSCALL(shutdown)
+SYSCALL(sigfillset)
+SYSCALL(sigprocmask)
+SYSCALL(sigwait)
+SYSCALL(alarm)
+SYSCALL(waitpid)
+SYSCALL(setsid)
+SYSCALL(mmap)
+SYSCALL(munmap)
+SYSCALL(delete)
+SYSCALL(show)
+SYSCALL(showstat)
+SYSCALL(ftruncate)
+SYSCALL(truncate)
+SYSCALL(rename)
+SYSCALL(symlink)
+SYSCALL(readlink)
+SYSCALL(getuid)
+SYSCALL(geteuid)
+SYSCALL(nanosleep)
+SYSCALL(mprotect)
+SYSCALL(ioctl)
+SYSCALL(getcwd)
+SYSCALL(arch_prctl)
+SYSCALL(set_tid_address)
+SYSCALL(set_robust_list)
+SYSCALL(futex)
+SYSCALL(clone)
+SYSCALL(exit_group)
+SYSCALL(wait4)
+SYSCALL(getgid)
+SYSCALL(getegid)
+SYSCALL(umask)
+SYSCALL(writev)
+SYSCALL(readv)
+SYSCALL(brk)
+SYSCALL(prlimit)
+SYSCALL(stat)
+SYSCALL(lstat)
+SYSCALL(access)
+SYSCALL(openat)
+SYSCALL(fchdir)
+SYSCALL(enable_linux_abi)
+SYSCALL(getrlimit)
+SYSCALL(setuid)
+SYSCALL(setgid)
+SYSCALL(getsid)
+SYSCALL(dup3)
+SYSCALL(pipe2)
+SYSCALL(clock_gettime)
+SYSCALL(getppid)
+SYSCALL(rt_sigaction)
+SYSCALL(shmget)
+SYSCALL(shmat)
+SYSCALL(shmdt)
+SYSCALL(socket)
+SYSCALL(bind)
+SYSCALL(listen)
+SYSCALL(accept)
+SYSCALL(connect)
+SYSCALL(sendto)
+SYSCALL(recvfrom)
+SYSCALL(sockshutdown)
+SYSCALL(socketpair)
+SYSCALL(setsockopt)
+SYSCALL(getsockopt)
+SYSCALL(mount)