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/CMakeLists.txt

@@ -75,6 +75,7 @@ if("${BANAN_ARCH}" STREQUAL "x86_64")
 		arch/x86_64/IDT.cpp
 		arch/x86_64/interrupts.S
 		arch/x86_64/PageTable.cpp
+		arch/x86_64/Signal.S
 		arch/x86_64/Thread.S
 	)
 elseif("${BANAN_ARCH}" STREQUAL "i386")

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)
 	{

kernel/include/kernel/Process.h

@@ -100,6 +100,10 @@ namespace Kernel
 		BAN::ErrorOr<long> sys_alloc(size_t);
 		BAN::ErrorOr<long> sys_free(void*);
 
+		BAN::ErrorOr<long> sys_signal(int, void (*)(int));
+		BAN::ErrorOr<long> sys_kill(pid_t pid, int signal);
+		BAN::ErrorOr<long> sys_raise(int signal, uintptr_t& return_rsp, uintptr_t& return_rip);
+
 		BAN::ErrorOr<long> sys_termid(char*) const;
 
 		BAN::ErrorOr<long> sys_clock_gettime(clockid_t, timespec*) const;

kernel/kernel/Process.cpp

@@ -14,6 +14,9 @@
 #include <stdio.h>
 #include <sys/sysmacros.h>
 
+extern "C" void signal_trampoline();
+extern "C" void test_signal();
+
 namespace Kernel
 {
 
@@ -788,6 +791,27 @@ namespace Kernel
 		return 0;
 	}
 
+	BAN::ErrorOr<long> Process::sys_raise(int signal, uintptr_t& return_rsp, uintptr_t& return_rip)
+	{
+		if (signal < _SIGMIN || signal > _SIGMAX)
+			return BAN::Error::from_errno(EINVAL);
+
+		ASSERT(&Process::current() == this);
+
+		LockGuard lock_guard(m_lock);
+		asm volatile("cli");
+
+		uintptr_t* return_rsp_ptr = (uintptr_t*)return_rsp;
+		*--return_rsp_ptr = return_rip;
+		*--return_rsp_ptr = signal;
+		*--return_rsp_ptr = (uintptr_t)test_signal;
+
+		return_rsp = (uintptr_t)return_rsp_ptr;
+		return_rip = (uintptr_t)signal_trampoline;
+
+		return 0;
+	}
+
 	BAN::ErrorOr<long> Process::sys_setuid(uid_t uid)
 	{
 		if (uid < 0 || uid >= 1'000'000'000)

kernel/kernel/Syscall.cpp

@@ -140,6 +140,9 @@ namespace Kernel
 		case SYS_DUP2:
 			ret = Process::current().sys_dup2((int)arg1, (int)arg2);
 			break;
+		case SYS_RAISE:
+			ret = Process::current().sys_raise((int)arg1, interrupt_stack.rsp, interrupt_stack.rip);
+			break;
 		default:
 			dwarnln("Unknown syscall {}", syscall);
 			break;

kernel/kernel/kernel.cpp

@@ -98,8 +98,8 @@ namespace BAN::Formatter
 
 }
 
-extern "C" uintptr_t g_kernel_start;
-extern "C" uintptr_t g_kernel_end;
+extern "C" uint8_t g_userspace_start[];
+extern "C" uint8_t g_userspace_end[];
 
 static void init2(void*);