Luna/kernel/src/sys/exec.cpp

#define MODULE "exec"

#include "errno.h"
#include "interrupts/Interrupts.h"
#include "kassert.h"
#include "log/Log.h"
#include "memory/MemoryManager.h"
#include "memory/PMM.h"
#include "memory/VMM.h"
#include "std/stdlib.h"
#include "std/string.h"
#include "sys/Syscall.h"
#include "sys/elf/ELFLoader.h"
#include "thread/Scheduler.h"

void sys_fork(Context* context)
{
    kinfoln("fork(): attempting fork");

    Task* parent = Scheduler::current_task();

    Task* child = Scheduler::create_user_task();
    if (!child)
    {
        context->rax = -ENOMEM;
        return;
    }

    if (!child->allocator.inherit(parent->allocator))
    {
        child->state = child->Exited;
        child->exit_status = -127; // so the reaper reaps it on next reaping
        context->rax = -ENOMEM;
        return;
    }

    child->save_context(context);
    child->save_floating();

    for (int i = 0; i < TASK_MAX_FDS; i++) { child->files[i] = parent->files[i]; }

    child->address_space = parent->address_space.clone();

    child->regs.rax = 0;
    context->rax = child->id;

    strlcpy(child->name, parent->name, sizeof(child->name));

    child->state = child->Running;

    kinfoln("fork(): forked parent %ld into child %ld", parent->id, child->id);

    return;
}

void sys_exec(Context* context, const char* pathname)
{
    char* kpathname = Syscall::strdup_from_user(pathname);
    if (!kpathname)
    {
        context->rax = -EFAULT;
        return;
    }

    kinfoln("exec(): executing %s", kpathname);

    VFS::Node* program = VFS::resolve_path(kpathname);
    if (!program)
    {
        kfree(kpathname);
        context->rax = -ENOENT;
        return;
    }

    if (program->type == VFS_DIRECTORY)
    {
        kfree(kpathname);
        context->rax = -EISDIR;
        return;
    }

    long memusage;
    if ((memusage = ELFLoader::check_elf_image(program)) < 0)
    {
        kfree(kpathname);
        context->rax = -ENOEXEC;
        return;
    }

    if ((uint64_t)memusage > PMM::get_free())
    {
        kfree(kpathname);
        context->rax = -ENOMEM;
        return;
    }

    Interrupts::disable();
    ASSERT(!Interrupts::are_enabled()); // This part is pretty sensitive.

    Task* task = Scheduler::current_task();
    ASSERT(task);

    // At this point, pretty much nothing can fail.

    task->allocator.free();
    task->allocator
        .init(); // If we had enough space for the old bitmap, we should have enough space for the new bitmap.

    task->address_space.clear();
    task->allocated_stack = (uint64_t)MemoryManager::get_pages_at(
        0x100000, TASK_PAGES_IN_STACK,
        MAP_USER | MAP_READ_WRITE); // If we had enough space for the old stack, there should be enough space for the
                                    // new stack.

    ELFImage* image = ELFLoader::load_elf_from_vfs(program);
    ASSERT(image); // If check_elf_image succeeded, load_elf_from_vfs MUST succeed, unless something has gone terribly
                   // wrong.

    strlcpy(task->name, kpathname, sizeof(task->name));

    Scheduler::reset_task(task, image);

    task->restore_context(context);

    kfree(kpathname);

    return;
}