/* Copyright (c) 2020 Johannes Stoelp */

#include "thread.h"

#include "arch/x86_64/asm.h"
#include "executor.h"

#include <cassert>
#include <cstdint>     // uintN_t
#include <sys/mman.h>  // mmap
#include <unistd.h>    // sysconf

namespace {
    static long get_pagesize() { return sysconf(_SC_PAGESIZE); }
}  // namespace

namespace nMatcha {
    Thread::Thread() {
        const long PAGE_SIZE = get_pagesize();
        const long STACK_SIZE = 8 * PAGE_SIZE;

        // create new stack
        void* stack = mmap(nullptr, STACK_SIZE, PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS, -1 /* fd */, 0 /* offset */);
        assert(stack != MAP_FAILED);

        // protect last stack page (lowest addr)
        int ret = mprotect(stack, PAGE_SIZE, PROT_NONE);
        assert(ret == 0);

        // stack grows downwards
        mStackPtr = static_cast<uint8_t*>(stack) + STACK_SIZE;
        {
            uint64_t* stack = static_cast<uint64_t*>(mStackPtr);
            *(--stack) = (uint64_t)this;
            *(--stack) = (uint64_t)Thread::entry;

            // initial values for yield epilog
            *(--stack) = (uint64_t)thread_create;
            *(--stack) = (uint64_t)0;

            // initial values for callee saved regs
            *(--stack) = (uint64_t)0;                                        // rbx
            *(--stack) = (uint64_t)(static_cast<uint64_t*>(mStackPtr) - 4);  // rbp
            *(--stack) = (uint64_t)0;                                        // r12
            *(--stack) = (uint64_t)0;                                        // r13
            *(--stack) = (uint64_t)0;                                        // r14
            *(--stack) = (uint64_t)0;                                        // r15

            mStackPtr = static_cast<void*>(stack);
        }
    }

    void Thread::entry(void* obj) {
        Thread* t = static_cast<Thread*>(obj);
        t->threadFn();
    }

    void Thread::yield() {
        assert(mExecutor);
        ::yield(mExecutor->getStackPtr(), &mStackPtr);
    }
}  // namespace nMatcha