1 files changed, 37 insertions, 0 deletions
diff --git a/lib/arch/arm64/init_stack.cc b/lib/arch/arm64/init_stack.cc
new file mode 100644
index 0000000..b28d957
--- /dev/null
+++ b/lib/arch/arm64/init_stack.cc
@@ -0,0 +1,37 @@
+#include <cassert>
+#include <cstdint>  // uintN_t
+
+extern "C" void thread_create();
+
+void* init_stack(void* stack_ptr, void (*entry)(void*), void* ctx) {
+    static_assert(sizeof(uint64_t) == sizeof(std::uintptr_t), "Pointer must be 64bit!");
+
+    // Setup initial stack frame which will be popped when yielding
+    // first time into the thread.
+    // Basic idea is to yield into Thread::entry() function which will
+    // then call the user function.
+
+    uint64_t* stack = static_cast<uint64_t*>(stack_ptr);
+    // Arguments for `thread_create`.
+    *(--stack) = reinterpret_cast<uint64_t>(ctx);
+    *(--stack) = reinterpret_cast<uint64_t>(entry);
+
+    // Yield epilogue.
+    *(--stack) = reinterpret_cast<uint64_t>(thread_create);  // x30 (LR)
+    *(--stack) = static_cast<uint64_t>(0);                   // x29 (FP)
+
+    // Callee saved registers.
+    *(--stack) = static_cast<uint64_t>(0);  // x28
+    *(--stack) = static_cast<uint64_t>(0);  // x27
+    *(--stack) = static_cast<uint64_t>(0);  // x26
+    *(--stack) = static_cast<uint64_t>(0);  // x25
+    *(--stack) = static_cast<uint64_t>(0);  // x24
+    *(--stack) = static_cast<uint64_t>(0);  // x23
+    *(--stack) = static_cast<uint64_t>(0);  // x22
+    *(--stack) = static_cast<uint64_t>(0);  // x21
+    *(--stack) = static_cast<uint64_t>(0);  // x20
+    *(--stack) = static_cast<uint64_t>(0);  // x19
+
+    assert((reinterpret_cast<std::uintptr_t>(stack) & 0xf) == 0);  // 16byte aligned
+    return static_cast<void*>(stack);
+}