9 files changed, 74 insertions, 2 deletions
diff --git a/src/kernel/proc.c b/src/kernel/proc.c
index 2e765c7..906fc29 100644
--- a/src/kernel/proc.c
+++ b/src/kernel/proc.c
@@ -50,7 +50,17 @@ struct process *process_fork(struct process *parent, int flags) {
 	struct process *child = kmalloc(sizeof *child);
 	memset(child, 0, sizeof *child);
 
-	child->pages = pagedir_copy(parent->pages);
+	if (flags & FORK_SHAREMEM) {
+		if (!parent->pages_refcount) {
+			parent->pages_refcount = kmalloc(sizeof *parent->pages_refcount);
+			*parent->pages_refcount = 1;
+		}
+		*parent->pages_refcount += 1;
+		child->pages_refcount = parent->pages_refcount;
+		child->pages = parent->pages;
+	} else {
+		child->pages = pagedir_copy(parent->pages);
+	}
 	child->regs  = parent->regs;
 	child->state = parent->state;
 	assert(child->state == PS_RUNNING); // not copying the state union
@@ -152,7 +162,16 @@ void process_kill(struct process *p, int ret) {
 			p->execbuf.buf = NULL;
 		}
 
-		pagedir_free(p->pages);
+		if (p->pages_refcount) {
+			assert(*p->pages_refcount != 0);
+			*p->pages_refcount -= 1;
+			if (*p->pages_refcount == 0) {
+				kfree(p->pages_refcount);
+				pagedir_free(p->pages);
+			}
+		} else {
+			pagedir_free(p->pages);
+		}
 
 		// TODO VULN unbounded recursion
 		struct process *c2;
diff --git a/src/kernel/proc.h b/src/kernel/proc.h
index 27327c4..e7946b2 100644
--- a/src/kernel/proc.h
+++ b/src/kernel/proc.h
@@ -20,6 +20,9 @@ enum process_state {
 
 struct process {
 	struct pagedir *pages;
+	/* if NULL, refcount == 1. kmalloc'd */
+	uint64_t *pages_refcount;
+
 	struct registers regs;
 	struct process *sibling, *child, *parent;
 
diff --git a/src/shared/include/camellia/flags.h b/src/shared/include/camellia/flags.h
index 5b8f834..30762bd 100644
--- a/src/shared/include/camellia/flags.h
+++ b/src/shared/include/camellia/flags.h
@@ -5,6 +5,7 @@
 
 #define FORK_NOREAP 1
 #define FORK_NEWFS 2
+#define FORK_SHAREMEM 4
 
 #define WRITE_TRUNCATE 1
 
diff --git a/src/user/app/tests/kernel/threads.c b/src/user/app/tests/kernel/threads.c
new file mode 100644
index 0000000..9f08c39
--- /dev/null
+++ b/src/user/app/tests/kernel/threads.c
@@ -0,0 +1,24 @@
+#include "../tests.h"
+#include <camellia/flags.h>
+#include <camellia/syscalls.h>
+#include <user/lib/esemaphore.h>
+#include <user/lib/thread.h>
+
+int global_n;
+
+static void basic_thread(void *sem) {
+	global_n = 10;
+	esem_signal(sem);
+}
+
+static void test_basic_thread(void) {
+	struct evil_sem *sem = esem_new(0);
+	global_n = 0;
+	thread_create(FORK_NOREAP, basic_thread, sem);
+	esem_wait(sem);
+	test(global_n == 10);
+}
+
+void r_k_threads(void) {
+	run_test(test_basic_thread);
+}
diff --git a/src/user/app/tests/tests.c b/src/user/app/tests/tests.c
index 2157e60..f9b085a 100644
--- a/src/user/app/tests/tests.c
+++ b/src/user/app/tests/tests.c
@@ -17,6 +17,7 @@ int main(void) {
 	r_k_misc();
 	r_k_miscsyscall();
 	r_k_path();
+	r_k_threads();
 	r_libc_esemaphore();
 	r_libc_string();
 	r_s_printf();
diff --git a/src/user/app/tests/tests.h b/src/user/app/tests/tests.h
index 79169c9..d092115 100644
--- a/src/user/app/tests/tests.h
+++ b/src/user/app/tests/tests.h
@@ -11,6 +11,7 @@ void r_k_fs(void);
 void r_k_misc(void);
 void r_k_miscsyscall(void);
 void r_k_path(void);
+void r_k_threads(void);
 void r_libc_esemaphore(void);
 void r_libc_string(void);
 void r_s_printf(void);
diff --git a/src/user/lib/thread.S b/src/user/lib/thread.S
new file mode 100644
index 0000000..3cd3500
--- /dev/null
+++ b/src/user/lib/thread.S
@@ -0,0 +1,8 @@
+.section .text
+.global chstack
+.type chstack, @function
+// _Noreturn void chstack(void *arg, void (*fn)(void*), void *esp);
+chstack:
+	mov %rdx, %rsp
+	call *%rsi
+	jmp 0 // "exit"
diff --git a/src/user/lib/thread.c b/src/user/lib/thread.c
new file mode 100644
index 0000000..25d98a9
--- /dev/null
+++ b/src/user/lib/thread.c
@@ -0,0 +1,11 @@
+#include <camellia/flags.h>
+#include <camellia/syscalls.h>
+#include <stdlib.h>
+#include <user/lib/thread.h>
+
+void thread_create(int flags, void (*fn)(void*), void *arg) {
+	if (!_syscall_fork(flags | FORK_SHAREMEM, NULL)) {
+		void *stack = malloc(4096);
+		chstack(arg, fn, stack + 4096);
+	}
+}
diff --git a/src/user/lib/thread.h b/src/user/lib/thread.h
new file mode 100644
index 0000000..0d7376a
--- /dev/null
+++ b/src/user/lib/thread.h
@@ -0,0 +1,4 @@
+#pragma once
+
+void thread_create(int flags, void (*fn)(void*), void *arg);
+_Noreturn void chstack(void *arg, void (*fn)(void*), void *esp);