Scheduler: clear user tasks' registers

This can be used later to implement execve()

kernel/include/sys/elf/ELFLoader.h

@@ -6,4 +6,5 @@ namespace ELFLoader
 {
     ELFImage* load_elf_from_address(uintptr_t addr);
     ELFImage* load_elf_from_filesystem(const char* filename);
+    void release_elf_image(ELFImage* image);
 }

kernel/include/thread/Scheduler.h

@@ -22,4 +22,6 @@ namespace Scheduler
 
     void reap_task(Task* task);
     void reap_tasks();
+
+    void reset_task(Task* task, ELFImage* new_image);
 }

kernel/include/thread/Task.h

@@ -36,6 +36,8 @@ struct Task
     char floating_region[512] __attribute__((aligned(16)));
     bool floating_saved = false;
 
+    bool user_task = true;
+
     bool is_user_task();
 
     ELFImage* image = nullptr;

kernel/src/sys/elf/ELFLoader.cpp

@@ -104,8 +104,10 @@ ELFImage* ELFLoader::load_elf_from_address(uintptr_t addr)
                 return 0;
             }
             uint64_t pages = Utilities::get_blocks_from_size(PAGE_SIZE, (phdr->p_vaddr % PAGE_SIZE) + phdr->p_memsz);
-            void* buffer = MemoryManager::get_pages_at(phdr->p_vaddr, pages,
-                                                       phdr->p_flags & 2 ? MAP_READ_WRITE | MAP_USER : MAP_USER);
+            void* buffer = (void*)((uint64_t)MemoryManager::get_pages_at(
+                                       Utilities::round_down_to_nearest_page(phdr->p_vaddr), pages,
+                                       phdr->p_flags & 2 ? MAP_READ_WRITE | MAP_USER : MAP_USER) +
+                                   (phdr->p_vaddr % PAGE_SIZE));
             memcpy(buffer, (void*)(addr + phdr->p_offset), phdr->p_filesz);
             memset((void*)((uint64_t)buffer + phdr->p_filesz), 0, phdr->p_memsz - phdr->p_filesz);
             image = (ELFImage*)krealloc(image, (sizeof(ELFImage) - sizeof(ELFSection)) +
@@ -123,4 +125,15 @@ ELFImage* ELFLoader::load_elf_from_address(uintptr_t addr)
         return 0;
     }
     return image;
+}
+
+void ELFLoader::release_elf_image(ELFImage* image)
+{
+    for (uint64_t i = 0; i < image->section_count; i++)
+    {
+        ELFSection& section = image->sections[i];
+        kdbgln("Freeing up section %lx, was using %ld pages", section.base, section.pages);
+        MemoryManager::release_pages((void*)Utilities::round_down_to_nearest_page(section.base), section.pages);
+    }
+    kfree(image);
 }

kernel/src/thread/Scheduler.cpp

@@ -41,6 +41,7 @@ void Scheduler::init()
     idle_task.regs.ss = 0x10;
     idle_task.regs.rflags = (1 << 21) | (1 << 9);
     idle_task.task_sleep = 1000;
+    idle_task.user_task = false;
     idle_task.state = idle_task.Idle;
 
     base_task = new Task;
@@ -51,6 +52,7 @@ void Scheduler::init()
     sched_current_task->next_task = sched_current_task;
     sched_current_task->prev_task = sched_current_task;
     sched_current_task->state = sched_current_task->Running;
+    sched_current_task->user_task = false;
     task_num++;
     // the other registers will be saved next task switch
 
@@ -61,6 +63,7 @@ void Scheduler::add_kernel_task(void (*task)(void))
 {
     Task* new_task = new Task;
     ASSERT(new_task);
+    new_task->user_task = false;
     new_task->id = free_tid++;
     new_task->regs.rip = (uint64_t)task;
     new_task->allocated_stack =
@@ -88,6 +91,8 @@ void Scheduler::add_user_task(void* task)
 {
     Task* new_task = new Task;
     ASSERT(new_task);
+    memset(&new_task->regs, 0, sizeof(Context));
+    new_task->user_task = true;
     new_task->id = free_tid++;
     new_task->regs.rip = (uint64_t)task;
     new_task->allocated_stack = (uint64_t)MemoryManager::get_pages(
@@ -116,6 +121,7 @@ void Scheduler::load_user_task(const char* filename)
     kinfoln("Loading user task: %s", filename);
     Task* new_task = new Task;
     ASSERT(new_task);
+    memset(&new_task->regs, 0, sizeof(Context));
     new_task->id = free_tid++;
     ELFImage* image = ELFLoader::load_elf_from_filesystem(filename);
     if (!image)
@@ -124,6 +130,7 @@ void Scheduler::load_user_task(const char* filename)
         delete new_task;
         return;
     }
+    new_task->user_task = true;
     new_task->regs.rip = image->entry;
     new_task->image = image;
     new_task->allocated_stack = (uint64_t)MemoryManager::get_pages(
@@ -147,6 +154,26 @@ void Scheduler::load_user_task(const char* filename)
             new_task->id, new_task->regs.rsp, task_num);
 }
 
+void Scheduler::reset_task(Task* task, ELFImage* new_image)
+{
+    memset(&task->regs, 0, sizeof(Context));
+    task->state = task->Running;
+    task->regs.rip = new_image->entry;
+    task->image = new_image;
+    task->allocated_stack = (uint64_t)MemoryManager::get_pages(
+        TASK_PAGES_IN_STACK, MAP_READ_WRITE | MAP_USER); // 16 KB is enough for everyone, right?
+    task->regs.rsp = Utilities::get_top_of_stack(task->allocated_stack, TASK_PAGES_IN_STACK);
+    task->regs.cs = 0x18 | 0x03;
+    task->regs.ss = 0x20 | 0x03;
+    task->regs.ds = 0x20 | 0x03;
+    task->regs.rflags = (1 << 21) | (1 << 9); // enable interrupts
+    task->task_sleep = 0;
+    task->task_time = 0;
+    task->cpu_time = 0;
+    kinfoln("Resetting task: loaded at %lx, tid %ld, stack at %lx, total tasks: %ld", task->regs.rip, task->id,
+            task->regs.rsp, task_num);
+}
+
 void Scheduler::reap_task(Task* task)
 {
     ASSERT(!Interrupts::is_in_handler());
@@ -158,14 +185,9 @@ void Scheduler::reap_task(Task* task)
         MemoryManager::release_pages((void*)exiting_task->allocated_stack, TASK_PAGES_IN_STACK);
     if (exiting_task->image) // FIXME: Also free pages the task has mmap-ed but not munmap-ed.
     {
-        for (uint64_t i = 0; i < exiting_task->image->section_count; i++)
-        {
-            ELFSection& section = exiting_task->image->sections[i];
-            kdbgln("Task was using region %lx, which used %ld pages", section.base, section.pages);
-            MemoryManager::release_pages((void*)section.base, section.pages);
-        }
-        kfree(exiting_task->image);
+        ELFLoader::release_elf_image(exiting_task->image);
     }
+    for (int i = 0; i < TASK_MAX_FDS; i++) { exiting_task->files[i].close(); }
     delete exiting_task;
 }
 

kernel/src/thread/Task.cpp

@@ -25,5 +25,5 @@ void task_restore_floating(Task& task)
 
 bool Task::is_user_task()
 {
-    return (regs.cs & 3) > 0;
+    return user_task;
 }