Luna/kernel/src/sys/exec.cpp

#define MODULE "exec"

#include "assert.h"
#include "errno.h"
#include "interrupts/Interrupts.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_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;
    }

    uint64_t allocated_stack = (uint64_t)MemoryManager::get_pages(TASK_PAGES_IN_STACK, MAP_READ_WRITE | MAP_USER);
    if (!allocated_stack)
    {
        kfree(kpathname);
        context->rax = -ENOMEM;
        return;
    }

    uint64_t allocated_stack_phys = VMM::get_physical(allocated_stack);

    if ((uint64_t)memusage > PMM::get_free())
    {
        kfree(kpathname);
        MemoryManager::release_pages((void*)allocated_stack, TASK_PAGES_IN_STACK);
        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.

    VMM::switch_back_to_kernel_address_space();

    task->address_space.destroy();
    task->address_space = AddressSpace::create();

    VMM::switch_to_user_address_space(task->address_space);
    VMM::apply_address_space();
    VMM::enter_syscall_context();

    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.

    task->allocated_stack = allocated_stack;

    for (uint64_t i = 0; i < TASK_PAGES_IN_STACK; i++)
    {
        VMM::map(allocated_stack + (i * PAGE_SIZE), allocated_stack_phys + (i * PAGE_SIZE), MAP_READ_WRITE | MAP_USER);
    }

    Scheduler::reset_task(task, image);

    set_context_from_task(*task, context);

    kfree(kpathname);

    return;
}