Kernel: Make signals more POSIX

kernel/include/kernel/Process.h

@@ -155,11 +155,15 @@ namespace Kernel
 		BAN::Vector<BAN::UniqPtr<FixedWidthAllocator>> m_fixed_width_allocators;
 		BAN::UniqPtr<GeneralAllocator> m_general_allocator;
 
+		vaddr_t m_signal_handlers[_SIGMAX + 1] { };
+
 		userspace_info_t m_userspace_info;
 		ExitStatus m_exit_status;
 
 		BAN::UniqPtr<PageTable> m_page_table;
 		BAN::RefPtr<TTY> m_tty;
+
+		friend class Thread;
 	};
 
 }

kernel/include/kernel/Thread.h

@@ -37,6 +37,7 @@ namespace Kernel
 		BAN::ErrorOr<Thread*> clone(Process*, uintptr_t rsp, uintptr_t rip);
 		void setup_exec();
 
+		bool has_signal_to_execute() const;
 		void handle_next_signal();
 		void handle_signal(int signal, uintptr_t& return_rsp, uintptr_t& return_rip);
 
@@ -88,9 +89,9 @@ namespace Kernel
 		bool						m_in_syscall		{ false };
 		bool						m_is_userspace		{ false };
 
-		BAN::CircularQueue<int, 10> m_signal_queue;
-		vaddr_t m_signal_handlers[_SIGMAX + 1] { };
-		uint64_t m_signal_mask { (1ull << SIGCHLD) | (1ull << SIGURG) };
+		BAN::CircularQueue<int, 10>	m_signal_queue;
+		uint64_t					m_signal_mask		{ 0 };
+		bool						m_handling_signal	{ false };
 		static_assert(_SIGMAX < 64);
 
 		friend class Process;

kernel/kernel/Process.cpp

@@ -97,7 +97,10 @@ namespace Kernel
 		, m_open_file_descriptors(m_credentials)
 		, m_pid(pid)
 		, m_tty(TTY::current())
-	{ }
+	{
+		for (size_t i = 0; i < sizeof(m_signal_handlers) / sizeof(*m_signal_handlers); i++)
+			m_signal_handlers[i] = (vaddr_t)SIG_DFL;
+	}
 
 	Process::~Process()
 	{
@@ -303,6 +306,7 @@ namespace Kernel
 		forked->m_fixed_width_allocators = BAN::move(fixed_width_allocators);
 		forked->m_general_allocator = BAN::move(general_allocator);
 		forked->m_userspace_info = m_userspace_info;
+		memcpy(forked->m_signal_handlers, m_signal_handlers, sizeof(m_signal_handlers));
 
 		ASSERT(this == &Process::current());
 		// FIXME: this should be able to fail
@@ -352,6 +356,9 @@ namespace Kernel
 
 			m_userspace_info.entry = elf->file_header_native().e_entry;
 
+			for (size_t i = 0; i < sizeof(m_signal_handlers) / sizeof(*m_signal_handlers); i++)
+				m_signal_handlers[i] = (vaddr_t)SIG_DFL;
+
 			// NOTE: we clear the elf since we don't need the memory anymore
 			elf.clear();
 
@@ -789,6 +796,16 @@ namespace Kernel
 		return 0;
 	}
 
+	BAN::ErrorOr<long> Process::sys_signal(int signal, void (*handler)(int))
+	{
+		if (signal < _SIGMIN || signal > _SIGMAX)
+			return BAN::Error::from_errno(EINVAL);
+
+		CriticalScope _;
+		m_signal_handlers[signal] = (vaddr_t)handler;
+		return 0;
+	}
+
 	BAN::ErrorOr<long> Process::sys_kill(pid_t pid, int signal, uintptr_t& return_rsp, uintptr_t& return_rip)
 	{
 		if (pid <= 0)

kernel/kernel/Scheduler.cpp

@@ -212,7 +212,7 @@ namespace Kernel
 				current.set_started();
 				start_thread(current.rsp(), current.rip());
 			case Thread::State::Executing:
-				while (!current.m_signal_queue.empty())
+				while (current.has_signal_to_execute())
 					current.handle_next_signal();
 				continue_thread(current.rsp(), current.rip());
 			case Thread::State::Terminating:

kernel/kernel/Thread.cpp

@@ -133,6 +133,8 @@ namespace Kernel
 		m_rsp = stack_base() + stack_size();
 		m_rip = (uintptr_t)entry_trampoline;
 
+		// Signal mask is inherited
+
 		// Setup stack for returning
 		{
 			// FIXME: don't use PageTableScope
@@ -143,6 +145,11 @@ namespace Kernel
 		}
 	}
 
+	bool Thread::has_signal_to_execute() const
+	{
+		return !m_signal_queue.empty() && !m_handling_signal;
+	}
+
 	void Thread::handle_next_signal()
 	{
 		ASSERT(!interrupts_enabled());
@@ -158,16 +165,24 @@ namespace Kernel
 		ASSERT(!m_signal_queue.empty());
 		ASSERT(m_signal_queue.front() == signal);
 
-		// Skip masked (ignored) signals
-		if (m_signal_mask & (1ull << signal))
-			return;
+		vaddr_t signal_handler = process().m_signal_handlers[signal];
 
-		if (m_signal_handlers[signal])
+		m_handling_signal = true;
+
+		// Skip masked and ignored signals
+		if (m_signal_mask & (1ull << signal))
+			;
+		else if (signal_handler == (vaddr_t)SIG_IGN)
+			;
+		else if (signal_handler != (vaddr_t)SIG_DFL)
 		{
 			write_to_stack(return_rsp, return_rip);
 			write_to_stack(return_rsp, signal);
-			write_to_stack(return_rsp, m_signal_handlers[signal]);
+			write_to_stack(return_rsp, signal_handler);
 			return_rip = (uintptr_t)signal_trampoline;
+
+			// FIXME: we should only mark this signal as done when
+			//        handler returns
 		}
 		else
 		{
@@ -226,6 +241,7 @@ namespace Kernel
 		}
 
 		m_signal_queue.pop();
+		m_handling_signal = false;
 	}
 
 	void Thread::validate_stack() const

libc/include/signal.h

@@ -9,10 +9,10 @@ __BEGIN_DECLS
 
 #include <time.h>
 
-#define SIG_DFL		1
-#define SIG_ERR		2
-#define SIG_HOLD	3
-#define SIG_IGN		4
+#define SIG_DFL		((void (*)(int))0)
+#define SIG_ERR		((void (*)(int))1)
+#define SIG_HOLD	((void (*)(int))2)
+#define SIG_IGN		((void (*)(int))3)
 
 #define __need_pthread_t
 #define __need_size_t