Implement initial fork syscall

src/drivers/nulldrv/main.s

@@ -6,6 +6,10 @@ _start:
 	int 0xee
 	mov r12, rax	; save pid to r12
 
+	mov rax, 8		; FORK syscall
+	int 0xee
+
+	mov r10, rax
 	mov rax, 1		; DEBUG syscall
 	int 0xee
 

src/kernel/cpu.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include <stdint.h>
+
 struct cpu_state
 {
 	uint64_t ds;

src/kernel/debug.cpp

@@ -2,6 +2,7 @@
 #include "cpu.h"
 #include "debug.h"
 #include "gdt.h"
+#include "page_manager.h"
 
 #define print_reg(name, value) cons->printf("         %s: %016lx\n", name, (value));
 
@@ -39,6 +40,9 @@ print_regs(const cpu_state &regs)
 
 	cons->puts("\n");
 	print_reg("rip", regs.rip);
+
+	cons->puts("\n");
+	print_reg("cr3", page_manager::get()->get_pml4());
 }
 
 void

src/kernel/interrupts.cpp

@@ -171,7 +171,7 @@ isr_handler(uintptr_t return_rsp, cpu_state *regs)
 			print_reg("rip", regs->rip);
 
 			cons->puts("\n");
-			print_stacktrace(2);
+			//print_stacktrace(2);
 		}
 		_halt();
 		break;

src/kernel/main.cpp

@@ -41,7 +41,7 @@ init_console()
 	//log::enable(logs::apic, log::level::debug);
 	//log::enable(logs::device, log::level::info);
 	log::enable(logs::driver, log::level::debug);
-	log::enable(logs::memory, log::level::info);
+	log::enable(logs::memory, log::level::debug);
 	log::enable(logs::fs, log::level::debug);
 	log::enable(logs::task, log::level::debug);
 	log::enable(logs::boot, log::level::debug);
@@ -148,7 +148,7 @@ kernel_main(popcorn_data *header)
 
 	for (auto &f : ird.files()) {
 		if (f.executable())
-			sched->create_process(f.name(), f.data(), f.size());
+			sched->load_process(f.name(), f.data(), f.size());
 	}
 
 	sched->start();

src/kernel/page_manager.cpp

@@ -92,12 +92,19 @@ page_table *
 page_manager::copy_table(page_table *from, page_table::level lvl)
 {
 	page_table *to = get_table_page();
+	log::debug(logs::memory, "Page manager copying level %d table at %016lx to %016lx.", lvl, from, to);
+
+	if (lvl == page_table::level::pml4) {
+		to->entries[510] = m_kernel_pml4->entries[510];
+		to->entries[511] = m_kernel_pml4->entries[511];
+	}
 
 	const int max =
 		lvl == page_table::level::pml4 ?
 			510 :
 			512;
 
+	unsigned pages_copied = 0;
 	for (int i = 0; i < max; ++i) {
 		if (!from->is_present(i)) {
 			to->entries[i] = 0;
@@ -112,6 +119,7 @@ page_manager::copy_table(page_table *from, page_table::level lvl)
 			uint16_t flags = from->entries[i] &  0xfffull;
 			uintptr_t orig = from->entries[i] & ~0xfffull;
 			to->entries[i] = copy_page(orig) | flags;
+			pages_copied++;
 		} else {
 			uint16_t flags = 0;
 			page_table *next_from = from->get(i, &flags);
@@ -120,6 +128,9 @@ page_manager::copy_table(page_table *from, page_table::level lvl)
 		}
 	}
 
+	if (pages_copied)
+		log::debug(logs::memory, "   copied %3u pages", pages_copied);
+
 	return to;
 }
 

src/kernel/process.cpp

@@ -1,7 +1,59 @@
+#include "cpu.h"
+#include "log.h"
 #include "process.h"
 #include "scheduler.h"
 
 
+pid_t
+process::fork(uintptr_t in_rsp)
+{
+	auto &sched = scheduler::get();
+	auto *child = sched.create_process();
+	kassert(child, "process::fork() got null child");
+
+	child->ppid = pid;
+	child->flags =
+		process_flags::running |
+		process_flags::ready;
+
+	sched.m_runlists[child->priority].push_back(child);
+
+	child->rsp = in_rsp;
+
+	child->pml4 = page_manager::get()->copy_table(pml4);
+	kassert(child->pml4, "process::fork() got null pml4");
+
+	child->setup_kernel_stack(kernel_stack_size, kernel_stack);
+	child->rsp = child->kernel_stack + (in_rsp - kernel_stack);
+
+	log::debug(logs::task, "Copied process %d to %d, new PML4 %016lx.",
+			pid, child->pid, child->pml4);
+	log::debug(logs::task, "  copied stack %016lx to %016lx, rsp %016lx to %016lx.",
+			kernel_stack, child->kernel_stack, in_rsp, child->rsp);
+
+	// Add in the faked fork return value
+	cpu_state *regs = reinterpret_cast<cpu_state *>(child->rsp);
+	regs->rax = 0;
+
+	return child->pid;
+}
+
+void *
+process::setup_kernel_stack(size_t size, uintptr_t orig)
+{
+	void *stack0 = kutil::malloc(size);
+
+	if (orig)
+		kutil::memcpy(stack0, reinterpret_cast<void*>(orig), size);
+	else
+		kutil::memset(stack0, 0, size);
+
+	kernel_stack_size = size;
+	kernel_stack = reinterpret_cast<uintptr_t>(stack0);
+
+	return stack0;
+}
+
 bool
 process::wait_on_signal(uint64_t sigmask)
 {

src/kernel/process.h

@@ -7,6 +7,8 @@
 #include "kutil/linked_list.h"
 #include "page_manager.h"
 
+typedef uint32_t pid_t;
+
 
 enum class process_flags : uint32_t
 {
@@ -33,8 +35,8 @@ enum class process_wait : uint8_t
 /// A process
 struct process
 {
-	uint32_t pid;
-	uint32_t ppid;
+	pid_t pid;
+	pid_t ppid;
 
 	process_flags flags;
 
@@ -52,6 +54,15 @@ struct process
 	uintptr_t rsp;
 	page_table *pml4;
 
+	uintptr_t kernel_stack;
+	size_t kernel_stack_size;
+
+	/// Copy this process.
+	/// \arg in_rsp The RSP of the calling process
+	/// \returns    Returns the child's pid to the parent, and
+	///             0 to the child.
+	pid_t fork(uint64_t in_rsp);
+
 	/// Unready this process until it gets a signal
 	/// \arg sigmask  A bitfield of signals to wake on
 	/// \returns  Whether the process should be rescheduled
@@ -104,6 +115,16 @@ struct process
 	/// \returns  True if this wake was handled
 	bool wake_on_receive(process *source);
 
+private:
+	friend class scheduler;
+
+	/// Set up a new kernel stack for this process, optionally copying the
+	/// given stack. Sets the kernel stack on the process object, but also
+	/// returns it.
+	/// \arg size  Size of the stack to allocate
+	/// \arg orig  Address of a stack to copy, or 0 for no copying.
+	/// \returns   The address of the new stack as a pointer
+	void * setup_kernel_stack(size_t size, uintptr_t orig);
 };
 
 using process_list = kutil::linked_list<process>;

src/kernel/scheduler.cpp

@@ -108,9 +108,20 @@ load_process(const void *image_start, size_t bytes, process *proc, cpu_state sta
 	log::debug(logs::task, "  Loaded! New process rip: %016lx", state.rip);
 }
 
-void
-scheduler::create_process(const char *name, const void *data, size_t size)
+process_node *
+scheduler::create_process()
 {
+	auto *proc = m_process_allocator.pop();
+	proc->pid = m_next_pid++;
+	proc->priority = default_priority;
+	return proc;
+}
+
+void
+scheduler::load_process(const char *name, const void *data, size_t size)
+{
+	auto *proc = create_process();
+
 	uint16_t kcs = (1 << 3) | 0; // Kernel CS is GDT entry 1, ring 0
 	uint16_t cs = (5 << 3) | 3;  // User CS is GDT entry 5, ring 3
 
@@ -121,8 +132,7 @@ scheduler::create_process(const char *name, const void *data, size_t size)
 	page_table *pml4 = page_manager::get()->create_process_map();
 
 	// Create a one-page kernel stack space
-	void *stack0 = kutil::malloc(stack_size);
-	kutil::memset(stack0, 0, stack_size);
+	void *stack0 = proc->setup_kernel_stack(stack_size, 0);
 
 	// Stack grows down, point to the end
 	void *sp0 = kutil::offset_pointer(stack0, stack_size);
@@ -150,12 +160,6 @@ scheduler::create_process(const char *name, const void *data, size_t size)
 	loader_state->rax = reinterpret_cast<uint64_t>(data);
 	loader_state->rbx = size;
 
-	uint16_t pid = m_next_pid++;
-	auto *proc = m_process_allocator.pop();
-
-	proc->pid = pid;
-	proc->ppid = 0; // TODO
-	proc->priority = default_priority;
 	proc->rsp = reinterpret_cast<uintptr_t>(loader_state);
 	proc->pml4 = pml4;
 	proc->quanta = process_quanta;

src/kernel/scheduler.h

@@ -34,7 +34,7 @@ public:
 	/// \arg name  Name of the program image
 	/// \arg data  Pointer to the image data
 	/// \arg size  Size of the program image, in bytes
-	void create_process(const char *name, const void *data, size_t size);
+	void load_process(const char *name, const void *data, size_t size);
 
 	/// Start the scheduler working. This may involve starting
 	/// timer interrupts or other preemption methods.
@@ -61,6 +61,12 @@ public:
 private:
 	friend uintptr_t syscall_dispatch(uintptr_t, cpu_state &);
 	friend uintptr_t isr_handler(uintptr_t, cpu_state*);
+	friend class process;
+
+	/// Create a new process object. This process will have its pid
+	/// set but nothing else.
+	/// \returns  The new process object
+	process_node * create_process();
 
 	/// Handle a timer tick
 	/// \arg rsp0  The stack pointer of the current interrupt handler

src/kernel/syscall.cpp

@@ -68,8 +68,8 @@ syscall_dispatch(uintptr_t return_rsp, cpu_state &regs)
 			auto *p = s.current();
 			p->wait_on_signal(-1ull);
 			cons->printf("\nProcess %u: Received PAUSE syscall\n", p->pid);
-			return_rsp = s.schedule(return_rsp);
 			cons->set_color();
+			return_rsp = s.schedule(return_rsp);
 		}
 		break;
 
@@ -118,6 +118,19 @@ syscall_dispatch(uintptr_t return_rsp, cpu_state &regs)
 		}
 		break;
 
+	case syscall::fork:
+		{
+			cons->set_color(11);
+			cons->printf("\nProcess %u: Received FORK syscall\n", p->pid);
+			cons->set_color();
+
+			pid_t pid = p->fork(return_rsp);
+			if (pid == scheduler::get().current()->pid)
+				pid = 0;
+			regs.rax = pid;
+		}
+		break;
+
 	default:
 		cons->set_color(9);
 		cons->printf("\nReceived unknown syscall: %02x\n", call);

src/kernel/syscall.h

@@ -6,14 +6,15 @@ struct cpu_state;
 
 enum class syscall : uint64_t
 {
-	noop,
-	debug,
-	message,
-	pause,
-	sleep,
-	getpid,
-	send,
-	receive,
+	noop           = 0x0000,
+	debug          = 0x0001,
+	message        = 0x0002,
+	pause          = 0x0003,
+	sleep          = 0x0004,
+	getpid         = 0x0005,
+	send           = 0x0006,
+	receive        = 0x0007,
+	fork           = 0x0008,
 
 	last_syscall
 };