diff --git a/Makefile b/Makefile
index 0cbe8717bdb3..874c0aec0f9c 100644
--- a/Makefile
+++ b/Makefile
@@ -1123,7 +1123,9 @@ archprepare: archheaders archscripts scripts prepare3 outputmakefile \
 	asm-generic $(version_h) $(autoksyms_h) include/generated/utsrelease.h
 
 prepare0: archprepare
+ifeq ($(findstring elf,$(if $(CONFIG_OUTPUT_FORMAT),$(CONFIG_OUTPUT_FORMAT),elf)),elf)
 	$(Q)$(MAKE) $(build)=scripts/mod
+endif
 	$(Q)$(MAKE) $(build)=.
 
 # All the preparing..
diff --git a/tools/lkl/lib/Build b/tools/lkl/lib/Build
index f2ee04366464..a7a3bff27bb1 100644
--- a/tools/lkl/lib/Build
+++ b/tools/lkl/lib/Build
@@ -1,8 +1,10 @@
 CFLAGS_config.o += -I$(srctree)/tools/perf/pmu-events
+CFLAGS_posix-host.o += -D_FILE_OFFSET_BITS=64
 
 liblkl-y += fs.o
 liblkl-y += iomem.o
 liblkl-y += jmp_buf.o
+liblkl-$(LKL_HOST_CONFIG_POSIX) += posix-host.o
 liblkl-y += utils.o
 liblkl-y += virtio_blk.o
 liblkl-y += virtio.o
diff --git a/tools/lkl/lib/posix-host.c b/tools/lkl/lib/posix-host.c
new file mode 100644
index 000000000000..c2b579433b12
--- /dev/null
+++ b/tools/lkl/lib/posix-host.c
@@ -0,0 +1,435 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <pthread.h>
+#include <stdlib.h>
+#include <sys/time.h>
+#include <time.h>
+#include <signal.h>
+#include <assert.h>
+#include <unistd.h>
+#include <errno.h>
+#include <string.h>
+#include <time.h>
+#include <stdint.h>
+#include <sys/uio.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/syscall.h>
+#include <poll.h>
+#include <lkl_host.h>
+#include "iomem.h"
+#include "jmp_buf.h"
+
+/* Let's see if the host has semaphore.h */
+#include <unistd.h>
+
+#ifdef _POSIX_SEMAPHORES
+#include <semaphore.h>
+/* TODO(pscollins): We don't support fork() for now, but maybe one day
+ * we will?
+ */
+#define SHARE_SEM 0
+#endif /* _POSIX_SEMAPHORES */
+
+static void print(const char *str, int len)
+{
+	int ret __attribute__((unused));
+
+	ret = write(STDOUT_FILENO, str, len);
+}
+
+struct lkl_mutex {
+	pthread_mutex_t mutex;
+};
+
+struct lkl_sem {
+#ifdef _POSIX_SEMAPHORES
+	sem_t sem;
+#else
+	pthread_mutex_t lock;
+	int count;
+	pthread_cond_t cond;
+#endif /* _POSIX_SEMAPHORES */
+};
+
+struct lkl_tls_key {
+	pthread_key_t key;
+};
+
+#define WARN_UNLESS(exp) do {						\
+		if (exp < 0)						\
+			lkl_printf("%s: %s\n", #exp, strerror(errno));	\
+	} while (0)
+
+static int _warn_pthread(int ret, char *str_exp)
+{
+	if (ret > 0)
+		lkl_printf("%s: %s\n", str_exp, strerror(ret));
+
+	return ret;
+}
+
+
+/* pthread_* functions use the reverse convention */
+#define WARN_PTHREAD(exp) _warn_pthread(exp, #exp)
+
+static struct lkl_sem *sem_alloc(int count)
+{
+	struct lkl_sem *sem;
+
+	sem = malloc(sizeof(*sem));
+	if (!sem)
+		return NULL;
+
+#ifdef _POSIX_SEMAPHORES
+	if (sem_init(&sem->sem, SHARE_SEM, count) < 0) {
+		lkl_printf("sem_init: %s\n", strerror(errno));
+		free(sem);
+		return NULL;
+	}
+#else
+	pthread_mutex_init(&sem->lock, NULL);
+	sem->count = count;
+	WARN_PTHREAD(pthread_cond_init(&sem->cond, NULL));
+#endif /* _POSIX_SEMAPHORES */
+
+	return sem;
+}
+
+static void sem_free(struct lkl_sem *sem)
+{
+#ifdef _POSIX_SEMAPHORES
+	WARN_UNLESS(sem_destroy(&sem->sem));
+#else
+	WARN_PTHREAD(pthread_cond_destroy(&sem->cond));
+	WARN_PTHREAD(pthread_mutex_destroy(&sem->lock));
+#endif /* _POSIX_SEMAPHORES */
+	free(sem);
+}
+
+static void sem_up(struct lkl_sem *sem)
+{
+#ifdef _POSIX_SEMAPHORES
+	WARN_UNLESS(sem_post(&sem->sem));
+#else
+	WARN_PTHREAD(pthread_mutex_lock(&sem->lock));
+	sem->count++;
+	if (sem->count > 0)
+		WARN_PTHREAD(pthread_cond_signal(&sem->cond));
+	WARN_PTHREAD(pthread_mutex_unlock(&sem->lock));
+#endif /* _POSIX_SEMAPHORES */
+
+}
+
+static void sem_down(struct lkl_sem *sem)
+{
+#ifdef _POSIX_SEMAPHORES
+	int err;
+
+	do {
+		err = sem_wait(&sem->sem);
+	} while (err < 0 && errno == EINTR);
+	if (err < 0 && errno != EINTR)
+		lkl_printf("sem_wait: %s\n", strerror(errno));
+#else
+	WARN_PTHREAD(pthread_mutex_lock(&sem->lock));
+	while (sem->count <= 0)
+		WARN_PTHREAD(pthread_cond_wait(&sem->cond, &sem->lock));
+	sem->count--;
+	WARN_PTHREAD(pthread_mutex_unlock(&sem->lock));
+#endif /* _POSIX_SEMAPHORES */
+}
+
+static struct lkl_mutex *mutex_alloc(int recursive)
+{
+	struct lkl_mutex *_mutex = malloc(sizeof(struct lkl_mutex));
+	pthread_mutex_t *mutex = NULL;
+	pthread_mutexattr_t attr;
+
+	if (!_mutex)
+		return NULL;
+
+	mutex = &_mutex->mutex;
+	WARN_PTHREAD(pthread_mutexattr_init(&attr));
+
+	/* PTHREAD_MUTEX_ERRORCHECK is *very* useful for debugging,
+	 * but has some overhead, so we provide an option to turn it
+	 * off.
+	 */
+#ifdef DEBUG
+	if (!recursive)
+		WARN_PTHREAD(pthread_mutexattr_settype(
+				     &attr, PTHREAD_MUTEX_ERRORCHECK));
+#endif /* DEBUG */
+
+	if (recursive)
+		WARN_PTHREAD(pthread_mutexattr_settype(
+				     &attr, PTHREAD_MUTEX_RECURSIVE));
+
+	WARN_PTHREAD(pthread_mutex_init(mutex, &attr));
+
+	return _mutex;
+}
+
+static void mutex_lock(struct lkl_mutex *mutex)
+{
+	WARN_PTHREAD(pthread_mutex_lock(&mutex->mutex));
+}
+
+static void mutex_unlock(struct lkl_mutex *_mutex)
+{
+	pthread_mutex_t *mutex = &_mutex->mutex;
+
+	WARN_PTHREAD(pthread_mutex_unlock(mutex));
+}
+
+static void mutex_free(struct lkl_mutex *_mutex)
+{
+	pthread_mutex_t *mutex = &_mutex->mutex;
+
+	WARN_PTHREAD(pthread_mutex_destroy(mutex));
+	free(_mutex);
+}
+
+static lkl_thread_t thread_create(void (*fn)(void *), void *arg)
+{
+	pthread_t thread;
+
+	if (WARN_PTHREAD(pthread_create(&thread, NULL, (void* (*)(void *))fn,
+					arg)))
+		return 0;
+	else
+		return (lkl_thread_t) thread;
+}
+
+static void thread_detach(void)
+{
+	WARN_PTHREAD(pthread_detach(pthread_self()));
+}
+
+static void thread_exit(void)
+{
+	pthread_exit(NULL);
+}
+
+static int thread_join(lkl_thread_t tid)
+{
+	if (WARN_PTHREAD(pthread_join((pthread_t)tid, NULL)))
+		return (-1);
+	else
+		return 0;
+}
+
+static lkl_thread_t thread_self(void)
+{
+	return (lkl_thread_t)pthread_self();
+}
+
+static int thread_equal(lkl_thread_t a, lkl_thread_t b)
+{
+	return pthread_equal((pthread_t)a, (pthread_t)b);
+}
+
+static struct lkl_tls_key *tls_alloc(void (*destructor)(void *))
+{
+	struct lkl_tls_key *ret = malloc(sizeof(struct lkl_tls_key));
+
+	if (WARN_PTHREAD(pthread_key_create(&ret->key, destructor))) {
+		free(ret);
+		return NULL;
+	}
+	return ret;
+}
+
+static void tls_free(struct lkl_tls_key *key)
+{
+	WARN_PTHREAD(pthread_key_delete(key->key));
+	free(key);
+}
+
+static int tls_set(struct lkl_tls_key *key, void *data)
+{
+	if (WARN_PTHREAD(pthread_setspecific(key->key, data)))
+		return (-1);
+	return 0;
+}
+
+static void *tls_get(struct lkl_tls_key *key)
+{
+	return pthread_getspecific(key->key);
+}
+
+static unsigned long long time_ns(void)
+{
+	struct timespec ts;
+
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+
+	return 1e9*ts.tv_sec + ts.tv_nsec;
+}
+
+static void *timer_alloc(void (*fn)(void *), void *arg)
+{
+	int err;
+	timer_t timer;
+	struct sigevent se =  {
+		.sigev_notify = SIGEV_THREAD,
+		.sigev_value = {
+			.sival_ptr = arg,
+		},
+		.sigev_notify_function = (void (*)(union sigval))fn,
+	};
+
+	err = timer_create(CLOCK_REALTIME, &se, &timer);
+	if (err)
+		return NULL;
+
+	return (void *)(long)timer;
+}
+
+static int timer_set_oneshot(void *_timer, unsigned long ns)
+{
+	timer_t timer = (timer_t)(long)_timer;
+	struct itimerspec ts = {
+		.it_value = {
+			.tv_sec = ns / 1000000000,
+			.tv_nsec = ns % 1000000000,
+		},
+	};
+
+	return timer_settime(timer, 0, &ts, NULL);
+}
+
+static void timer_free(void *_timer)
+{
+	timer_t timer = (timer_t)(long)_timer;
+
+	timer_delete(timer);
+}
+
+static void panic(void)
+{
+	assert(0);
+}
+
+static long _gettid(void)
+{
+#ifdef	__FreeBSD__
+	return (long)pthread_self();
+#else
+	return syscall(SYS_gettid);
+#endif
+}
+
+struct lkl_host_operations lkl_host_ops = {
+	.panic = panic,
+	.thread_create = thread_create,
+	.thread_detach = thread_detach,
+	.thread_exit = thread_exit,
+	.thread_join = thread_join,
+	.thread_self = thread_self,
+	.thread_equal = thread_equal,
+	.sem_alloc = sem_alloc,
+	.sem_free = sem_free,
+	.sem_up = sem_up,
+	.sem_down = sem_down,
+	.mutex_alloc = mutex_alloc,
+	.mutex_free = mutex_free,
+	.mutex_lock = mutex_lock,
+	.mutex_unlock = mutex_unlock,
+	.tls_alloc = tls_alloc,
+	.tls_free = tls_free,
+	.tls_set = tls_set,
+	.tls_get = tls_get,
+	.time = time_ns,
+	.timer_alloc = timer_alloc,
+	.timer_set_oneshot = timer_set_oneshot,
+	.timer_free = timer_free,
+	.print = print,
+	.mem_alloc = malloc,
+	.mem_free = free,
+	.ioremap = lkl_ioremap,
+	.iomem_access = lkl_iomem_access,
+	.virtio_devices = lkl_virtio_devs,
+	.gettid = _gettid,
+	.jmp_buf_set = jmp_buf_set,
+	.jmp_buf_longjmp = jmp_buf_longjmp,
+};
+
+static int fd_get_capacity(struct lkl_disk disk, unsigned long long *res)
+{
+	off_t off;
+
+	off = lseek(disk.fd, 0, SEEK_END);
+	if (off < 0)
+		return (-1);
+
+	*res = off;
+	return 0;
+}
+
+static int do_rw(ssize_t (*fn)(), struct lkl_disk disk, struct lkl_blk_req *req)
+{
+	off_t off = req->sector * 512;
+	void *addr;
+	int len;
+	int i;
+	int ret = 0;
+
+	for (i = 0; i < req->count; i++) {
+
+		addr = req->buf[i].iov_base;
+		len = req->buf[i].iov_len;
+
+		do {
+			ret = fn(disk.fd, addr, len, off);
+
+			if (ret <= 0) {
+				ret = -1;
+				goto out;
+			}
+
+			addr += ret;
+			len -= ret;
+			off += ret;
+
+		} while (len);
+	}
+
+out:
+	return ret;
+}
+
+static int blk_request(struct lkl_disk disk, struct lkl_blk_req *req)
+{
+	int err = 0;
+
+	switch (req->type) {
+	case LKL_DEV_BLK_TYPE_READ:
+		err = do_rw(pread, disk, req);
+		break;
+	case LKL_DEV_BLK_TYPE_WRITE:
+		err = do_rw(pwrite, disk, req);
+		break;
+	case LKL_DEV_BLK_TYPE_FLUSH:
+	case LKL_DEV_BLK_TYPE_FLUSH_OUT:
+#ifdef __linux__
+		err = fdatasync(disk.fd);
+#else
+		err = fsync(disk.fd);
+#endif
+		break;
+	default:
+		return LKL_DEV_BLK_STATUS_UNSUP;
+	}
+
+	if (err < 0)
+		return LKL_DEV_BLK_STATUS_IOERR;
+
+	return LKL_DEV_BLK_STATUS_OK;
+}
+
+struct lkl_dev_blk_ops lkl_dev_blk_ops = {
+	.get_capacity = fd_get_capacity,
+	.request = blk_request,
+};
+
