Kernel/LibC: Add bareboness signals

You can now call raise() to raise a signal. Signal handlers are
not yet supported, but the handling works :)

kernel/arch/x86_64/PageTable.cpp

@@ -11,6 +11,9 @@ extern uint8_t g_kernel_end[];
 extern uint8_t g_kernel_execute_start[];
 extern uint8_t g_kernel_execute_end[];
 
+extern uint8_t g_userspace_start[];
+extern uint8_t g_userspace_end[];
+
 namespace Kernel
 {
 	
@@ -120,6 +123,14 @@ namespace Kernel
 			g_kernel_execute_end - g_kernel_execute_start,
 			Flags::Execute | Flags::Present
 		);
+
+		// Map userspace memory
+		map_range_at(
+			V2P(g_userspace_start),
+			(vaddr_t)g_userspace_start,
+			g_userspace_end - g_userspace_start,
+			Flags::Execute | Flags::UserSupervisor | Flags::Present
+		);
 	}
 
 	BAN::ErrorOr<PageTable*> PageTable::create_userspace()

kernel/arch/x86_64/Signal.S

@@ -0,0 +1,51 @@
+.section .userspace, "aw"
+
+.global signal_trampoline
+signal_trampoline:
+	pushq %rax
+	pushq %rbx
+	pushq %rcx
+	pushq %rdx
+	pushq %rbp
+	pushq %rdi
+	pushq %rsi
+	pushq %r8
+	pushq %r9
+	pushq %r10
+	pushq %r11
+	pushq %r12
+	pushq %r13
+	pushq %r14
+	pushq %r15
+
+	xchgw %bx, %bx
+
+	movq 128(%rsp), %rdi
+	movq 120(%rsp), %rax
+	call *%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
+	popq %rax
+
+	addq $16, %rsp
+
+	ret
+
+.global test_signal
+test_signal:
+	movq $99, %rax
+	int $0x80
+	ret

kernel/arch/x86_64/linker.ld

@@ -11,7 +11,13 @@ SECTIONS
 	{
 		g_kernel_execute_start = .;
 		*(.multiboot)
-		*(.text)
+		*(.text.*)
+	}
+	.userspace ALIGN(4K) : AT(ADDR(.userspace) - KERNEL_OFFSET)
+	{
+		g_userspace_start = .;
+		*(.userspace)
+		g_userspace_end = .;
 	}
 	.rodata ALIGN(4K) : AT(ADDR(.rodata) - KERNEL_OFFSET)
 	{