1 files changed, 39 insertions, 0 deletions
diff --git a/lib/arch/riscv64/init_stack.cc b/lib/arch/riscv64/init_stack.cc
new file mode 100644
index 0000000..94dab1c
--- /dev/null
+++ b/lib/arch/riscv64/init_stack.cc
@@ -0,0 +1,39 @@
+/* Copyright (c) 2021 Johannes Stoelp */
+
+#include <cassert>
+#include <cstdint>  // uintN_t
+
+extern "C" void thread_create();
+
+void* init_stack(void* stack_ptr, void (*entry)(void*), const 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);  // Return address (ra)
+
+    // Callee saved registers.
+    *(--stack) = static_cast<uint64_t>(0);  // x8
+    *(--stack) = static_cast<uint64_t>(0);  // x9
+    *(--stack) = static_cast<uint64_t>(0);  // x18
+    *(--stack) = static_cast<uint64_t>(0);  // x19
+    *(--stack) = static_cast<uint64_t>(0);  // x20
+    *(--stack) = static_cast<uint64_t>(0);  // x21
+    *(--stack) = static_cast<uint64_t>(0);  // x22
+    *(--stack) = static_cast<uint64_t>(0);  // x23
+    *(--stack) = static_cast<uint64_t>(0);  // x24
+    *(--stack) = static_cast<uint64_t>(0);  // x25
+    *(--stack) = static_cast<uint64_t>(0);  // x26
+    *(--stack) = static_cast<uint64_t>(0);  // x27
+
+    return static_cast<void*>(stack);
+}