Handout

kernel/arch/context.cc

@@ -0,0 +1,39 @@
+#include "context.h"
+
+#include "../debug/assert.h"
+#include "../debug/kernelpanic.h"
+
+/*! \brief Panic function
+ *
+ * If the kickoff function (assigned in \ref prepareContext) *returns*, this
+ * parameterless function will be called -- and stop the execution.
+ */
+static void panic() {
+	// we should not come back here
+	kernelpanic("Application should not return from context_kickoff");
+}
+
+void prepareContext(void* tos, Context& context,
+					void (*kickoff)(uintptr_t, uintptr_t, uintptr_t),
+					uintptr_t param1, uintptr_t param2, uintptr_t param3) {
+	assert(tos != nullptr && "Top Of Stack must not be nullptr");
+	assert((uintptr_t)tos % 16 == 0 && "Top Of Stack be 16 byte aligned");
+	assert(kickoff != nullptr && "Kickoff function missing");
+
+	// XXX Double check alignment. This seems to work, but the stack pointer for
+	// `panic` should not be aligned to 16-bit?
+	void** sp = reinterpret_cast<void**>(tos);
+	*(--sp) = reinterpret_cast<void*>(panic);	 // return address
+	*(--sp) = reinterpret_cast<void*>(kickoff);	 // start the thread in C land
+	*(--sp) = reinterpret_cast<void*>(fake_systemv_abi);  // pass via registers
+
+	context = {
+		.rbx = 0,
+		.rbp = 0,
+		.r12 = 0,
+		.r13 = param3,
+		.r14 = param2,	// Second parameter to kickoff
+		.r15 = param1,	// First parameter to kickoff
+		.rsp = reinterpret_cast<void*>(sp),
+	};
+}