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/* 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
*(--stack) = static_cast<uint64_t>(0); // rbp
// Callee saved registers.
*(--stack) = static_cast<uint64_t>(0); // rbx
*(--stack) = reinterpret_cast<uint64_t>(static_cast<uint64_t*>(stack_ptr) - 4); // rbp
*(--stack) = static_cast<uint64_t>(0); // r12
*(--stack) = static_cast<uint64_t>(0); // r13
*(--stack) = static_cast<uint64_t>(0); // r14
*(--stack) = static_cast<uint64_t>(0); // r15
assert((reinterpret_cast<std::uintptr_t>(stack) & 0xf) == 0); // 16byte aligned
return static_cast<void*>(stack);
}
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