Kernel/Userspace: Start initial work on userspace and syscalls

kernel/Makefile

@@ -26,11 +26,11 @@ CFLAGS:=$(CFLAGS) $(KERNEL_ARCH_CFLAGS)
 CPPFLAGS:=$(CPPFLAGS) $(KERNEL_ARCH_CPPFLAGS)
 LDFLAGS:=$(LDFLAGS) $(KERNEL_ARCH_LDFLAGS)
 LIBS:=$(LIBS) $(KERNEL_ARCH_LIBS)
-
+ 
 ifeq ($(UBSAN), 1)
 CFLAGS:=$(CFLAGS) -fsanitize=undefined
 endif
-
+ 
 BUILDDIR=$(abspath build)
  
 KERNEL_OBJS=					\
@@ -58,9 +58,11 @@ kernel/SpinLock.o				\
 kernel/SSP.o					\
 kernel/Storage/ATAController.o	\
 kernel/Storage/StorageDevice.o	\
+kernel/Syscall.o				\
 kernel/Thread.o					\
 kernel/TTY.o					\
 kernel/VesaTerminalDriver.o		\
+userspace/userspace.o			\
 icxxabi.o						\
 ubsan.o							\
  
@@ -109,6 +111,7 @@ always:
 	mkdir -p $(BUILDDIR)/kernel
 	mkdir -p $(BUILDDIR)/kernel/FS
 	mkdir -p $(BUILDDIR)/kernel/Storage
+	mkdir -p $(BUILDDIR)/userspace
 	mkdir -p $(BUILDDIR)/font
 
 clean:

kernel/arch/i386/IDT.cpp

@@ -151,6 +151,29 @@ found:
 		"popa;"
 		"iret;"
 	);
+	
+	extern "C" void syscall_asm();
+	asm(
+	".global syscall_asm;"
+	"syscall_asm:"
+		"pusha;"
+		"pushw %ds;"
+		"pushw %es;"
+		"pushw %ss;"
+		"pushw %ss;"
+		"popw %ds;"
+		"popw %es;"
+		"pushl %edx;"
+		"pushl %ecx;"
+		"pushl %ebx;"
+		"pushl %eax;"
+		"call cpp_syscall_handler;"
+		"addl $16, %esp;"
+		"popw %es;"
+		"popw %ds;"
+		"popa;"
+		"iret;"
+	);
 
 	static void flush_idt()
 	{
@@ -175,6 +198,12 @@ found:
 		flush_idt();
 	}
 
+	void register_syscall_handler(uint8_t offset, void(*handler)())
+	{
+		register_interrupt_handler(offset, handler);
+		s_idt[offset].DPL = 3;
+	}
+
 	void initialize()
 	{
 		constexpr size_t idt_size = 0x100 * sizeof(GateDescriptor);
@@ -219,6 +248,8 @@ found:
 		REGISTER_HANDLER(0x1E);
 		REGISTER_HANDLER(0x1F);
 
+		register_syscall_handler(0x80, syscall_asm);
+
 		flush_idt();
 	}
 

kernel/arch/i386/linker.ld

@@ -11,7 +11,9 @@ SECTIONS
 	}
 	.rodata BLOCK(4K) : ALIGN(4K)
 	{
-		*(.rodata)
+		g_rodata_start = .;
+		*(.rodata.*)
+		g_rodata_end = .;
 	}
 	.data BLOCK(4K) : ALIGN(4K)
 	{
@@ -24,4 +26,13 @@ SECTIONS
 	}
 
 	g_kernel_end = .;
+
+	. = 0x00A00000;
+
+	g_userspace_start = .;
+	.userspace BLOCK(4K) : ALIGN(4K)
+	{
+		*(.userspace)
+	}
+	g_userspace_end = .;
 }

kernel/arch/x86_64/IDT.cpp

@@ -148,6 +148,12 @@ namespace IDT
 		descriptor.flags = 0x8E;
 	}
 
+	static void register_syscall_handler(uint8_t index, void(*handler)())
+	{
+		register_interrupt_handler(index, handler);
+		s_idt[index].flags = 0xEE;
+	}
+
 	void register_irq_handler(uint8_t irq, void(*handler)())
 	{
 		s_irq_handlers[irq] = handler;
@@ -203,6 +209,8 @@ namespace IDT
 	extern "C" void irq14();
 	extern "C" void irq15();
 
+	extern "C" void syscall_asm();
+
 	void initialize()
 	{
 		s_idt = (GateDescriptor*)kmalloc(0x100 * sizeof(GateDescriptor));
@@ -262,6 +270,8 @@ namespace IDT
 		REGISTER_IRQ_HANDLER(14);
 		REGISTER_IRQ_HANDLER(15);
 
+		register_syscall_handler(0x80, syscall_asm);
+
 		flush_idt();
 	}
 

kernel/arch/x86_64/interrupts.S

@@ -34,6 +34,23 @@
 	popq %rax
 .endm
 
+.macro popaq_no_rax
+	popq %r15
+	popq %r14
+	popq %r13
+	popq %r12
+	popq %r11
+	popq %r10
+	popq %r9
+	popq %r8
+	popq %rsi
+	popq %rdi
+	popq %rbp
+	popq %rdx
+	popq %rcx
+	popq %rbx
+.endm
+
 isr_stub:
 	pushaq
 
@@ -138,3 +155,15 @@ irq 12
 irq 13
 irq 14
 irq 15
+
+.global syscall_asm
+syscall_asm:
+	cli
+	pushaq
+	movq %rax, %rdi
+	movq %rbx, %rsi
+	xchgq %rcx, %rdx
+	call cpp_syscall_handler
+	popaq_no_rax
+	addq $8, %rsp
+	iretq

kernel/arch/x86_64/linker.ld

@@ -11,7 +11,9 @@ SECTIONS
 	}
 	.rodata BLOCK(4K) : ALIGN(4K)
 	{
-		*(.rodata)
+		g_rodata_start = .;
+		*(.rodata.*)
+		g_rodata_end = .;
 	}
 	.data BLOCK(4K) : ALIGN(4K)
 	{
@@ -22,6 +24,15 @@ SECTIONS
 		*(COMMON)
 		*(.bss)
 	}
-
 	g_kernel_end = .;
+
+	. = 0x00A00000;
+
+	g_userspace_start = .;
+	.userspace BLOCK(4K) : ALIGN(4K)
+	{
+		*(.userspace)
+	}
+	g_userspace_end = .;
+
 }

kernel/include/kernel/Syscall.h

@@ -0,0 +1,4 @@
+#pragma once
+
+#define SYS_TEST 0
+#define SYS_PUTC 1

kernel/kernel/Syscall.cpp

@@ -0,0 +1,44 @@
+#include <kernel/Debug.h>
+#include <kernel/kprint.h>
+#include <kernel/Syscall.h>
+
+namespace Kernel
+{
+
+	int sys_test()
+	{
+		dprintln("hello");
+		return 0;
+	}
+
+	int sys_putc(void* ch)
+	{
+		kprint("{}", (char)(uintptr_t)ch);
+		return 0;
+	}
+
+	extern "C" int cpp_syscall_handler(int syscall, void* arg1, void* arg2, void* arg3)
+	{
+		(void)arg1;
+		(void)arg2;
+		(void)arg3;
+
+		int ret;
+		switch (syscall)
+		{
+		case SYS_TEST:
+			ret = sys_test();
+			break;
+		case SYS_PUTC:
+			ret = sys_putc(arg1);
+			break;
+		default:
+			ret = -1;
+			dprintln("Unknown syscall");
+			break;
+		}
+
+		return ret;
+	}
+
+}

kernel/kernel/kernel.cpp

@@ -1,3 +1,4 @@
+#include <kernel/Arch.h>
 #include <kernel/Debug.h>
 #include <kernel/FS/VirtualFileSystem.h>
 #include <kernel/GDT.h>
@@ -14,6 +15,7 @@
 #include <kernel/Scheduler.h>
 #include <kernel/Serial.h>
 #include <kernel/Shell.h>
+#include <kernel/Syscall.h>
 #include <kernel/TTY.h>
 #include <kernel/VesaTerminalDriver.h>
 
@@ -75,6 +77,14 @@ namespace BAN::Formatter
 
 }
 
+extern "C" uintptr_t g_rodata_start;
+extern "C" uintptr_t g_rodata_end;
+
+extern "C" uintptr_t g_userspace_start;
+extern "C" uintptr_t g_userspace_end;
+
+extern void userspace_entry();
+
 extern "C" void kernel_main()
 {
 	using namespace Kernel;
@@ -124,6 +134,50 @@ extern "C" void kernel_main()
 
 	MUST(Scheduler::initialize());
 	Scheduler& scheduler = Scheduler::get();
+#if 1
+	MUST(scheduler.add_thread(MUST(Thread::create(
+		[] (void*)
+		{
+			MMU::get().allocate_range((uintptr_t)&g_userspace_start, (uintptr_t)&g_userspace_end - (uintptr_t)&g_userspace_start, MMU::Flags::UserSupervisor | MMU::Flags::Present);
+			MMU::get().allocate_range((uintptr_t)&g_rodata_start,    (uintptr_t)&g_rodata_end    - (uintptr_t)&g_rodata_start,    MMU::Flags::UserSupervisor | MMU::Flags::Present);
+
+			void* userspace_stack = kmalloc(4096, 4096);
+			ASSERT(userspace_stack);
+			MMU::get().allocate_page((uintptr_t)userspace_stack, MMU::Flags::UserSupervisor | MMU::Flags::ReadWrite | MMU::Flags::Present);
+
+			BOCHS_BREAK();
+
+#if ARCH(x86_64)
+			asm volatile(
+				"pushq %0;"
+				"pushq %1;"
+				"pushfq;"
+				"pushq %2;"
+				"pushq %3;"
+				"iretq;"
+				:: "r"((uintptr_t)0x20 | 3), "r"((uintptr_t)userspace_stack + 4096), "r"((uintptr_t)0x18 | 3), "r"(userspace_entry)
+			);
+#else
+			asm volatile(
+				"movl %0, %%eax;"
+				"movw %%ax, %%ds;"
+				"movw %%ax, %%es;"
+				"movw %%ax, %%fs;"
+				"movw %%ax, %%gs;"
+
+				"movl %1, %%esp;"
+				"pushl %0;"
+				"pushl %1;"
+				"pushfl;"
+				"pushl %2;"
+				"pushl %3;"
+				"iret;"
+				:: "r"((uintptr_t)0x20 | 3), "r"((uintptr_t)userspace_stack + 4096), "r"((uintptr_t)0x18 | 3), "r"(userspace_entry)
+			);
+#endif
+		}
+	))));
+#else
 	MUST(scheduler.add_thread(MUST(Thread::create(
 		[](void* terminal_driver)
 		{
@@ -144,6 +198,7 @@ extern "C" void kernel_main()
 			shell->run();
 		}, tty1
 	))));
+#endif
 	scheduler.start();
 	ASSERT(false);
 }

kernel/userspace/userspace.cpp

@@ -0,0 +1,28 @@
+#include <BAN/Formatter.h>
+#include <kernel/Syscall.h>
+
+#define USERSPACE __attribute__((section(".userspace")))
+
+USERSPACE int syscall(int syscall, void* arg1 = nullptr, void* arg2 = nullptr, void* arg3 = nullptr)
+{
+	int ret;
+	asm volatile("int $0x80" : "=a"(ret) : "a"(syscall), "b"(arg1), "c"(arg2), "d"(arg3) : "memory");
+	return ret;
+}
+
+USERSPACE void user_putc(char ch)
+{
+	syscall(SYS_PUTC, (void*)(uintptr_t)ch);
+}
+
+USERSPACE void print(const char* str)
+{
+	while (*str)
+		user_putc(*str++);
+}
+
+USERSPACE void userspace_entry()
+{
+	BAN::Formatter::println(user_putc, "Hello {}!", "World");
+	for (;;);
+}