add forgotten libkernel.c

1 files changed, 12 insertions, 0 deletions

diff --git a/libkernel.c b/libkernel.c
new file mode 100644
index 0000000..0955e0e
--- /dev/null
+++ b/libkernel.c
@@ -0,0 +1,12 @@
+// This is the privileged code, that gets placed somewhere in
+// unprivileged process' address space. It's compiled as relocatable,
+// so it can be loaded at different address for different processes.
+
+void call_unprivileged(void (*address) (void)) {
+  // switch to PL0
+  asm("cps #0b10000\n\r"
+      "isb" ::: "memory");
+
+  // jump to that unprivileged code
+  address();
+}