hw: send exception signals and support single-stepping

Fixes #4975

repos/base-hw/src/core/kernel/core_interface.h

@@ -14,6 +14,9 @@
 #ifndef _CORE__KERNEL__CORE_INTERFACE_H_
 #define _CORE__KERNEL__CORE_INTERFACE_H_
 
+/* base includes */
+#include <cpu/cpu_state.h>
+
 /* base-internal includes */
 #include <base/internal/native_utcb.h>
 
@@ -31,6 +34,7 @@ namespace Kernel {
 	class Vm;
 	class User_irq;
 	using Native_utcb = Genode::Native_utcb;
+	using Cpu_state   = Genode::Cpu_state;
 	template <typename T> class Core_object_identity;
 
 	/**
@@ -58,6 +62,10 @@ namespace Kernel {
 	constexpr Call_arg call_id_new_obj()                { return 121; }
 	constexpr Call_arg call_id_delete_obj()             { return 122; }
 	constexpr Call_arg call_id_new_core_thread()        { return 123; }
+	constexpr Call_arg call_id_get_cpu_state()          { return 124; }
+	constexpr Call_arg call_id_set_cpu_state()          { return 125; }
+	constexpr Call_arg call_id_exception_state()        { return 126; }
+	constexpr Call_arg call_id_single_step()            { return 127; }
 
 	/**
 	 * Invalidate TLB entries for the `pd` in region `addr`, `sz`
@@ -159,6 +167,42 @@ namespace Kernel {
 	{
 		call(call_id_ack_irq(), (Call_arg) &irq);
 	}
+
+
+	/**
+	 * Get CPU state
+	 *
+	 * \param thread        pointer to thread kernel object
+	 * \param thread_state  pointer to result CPU state object
+	 */
+	inline void get_cpu_state(Thread & thread, Cpu_state & cpu_state)
+	{
+		call(call_id_get_cpu_state(), (Call_arg)&thread, (Call_arg)&cpu_state);
+	}
+
+
+	/**
+	 * Set CPU state
+	 *
+	 * \param thread        pointer to thread kernel object
+	 * \param thread_state  pointer to CPU state object
+	 */
+	inline void set_cpu_state(Thread & thread, Cpu_state & cpu_state)
+	{
+		call(call_id_set_cpu_state(), (Call_arg)&thread, (Call_arg)&cpu_state);
+	}
+
+
+	/**
+	 * Enable/disable single-stepping
+	 *
+	 * \param thread  pointer to thread kernel object
+	 * \param on      enable or disable
+	 */
+	inline void single_step(Thread & thread, bool & on)
+	{
+		call(call_id_single_step(), (Call_arg)&thread, (Call_arg)&on);
+	}
 }
 
 #endif /* _CORE__KERNEL__CORE_INTERFACE_H_ */

repos/base-hw/src/core/kernel/thread.cc

@@ -403,6 +403,7 @@ bool Thread::_restart()
 {
 	assert(_state == ACTIVE || _state == AWAITS_RESTART);
 	if (_state != AWAITS_RESTART) { return false; }
+	_exception_state = NO_EXCEPTION;
 	_become_active();
 	return true;
 }
@@ -793,6 +794,34 @@ void Kernel::Thread::_call_invalidate_tlb()
 }
 
 
+void Thread::_call_get_cpu_state() {
+	Thread &thread = *(Thread*)user_arg_1();
+	Cpu_state &cpu_state = *(Cpu_state*)user_arg_2();
+	cpu_state = *thread.regs;
+}
+
+
+void Thread::_call_set_cpu_state() {
+	Thread &thread = *(Thread*)user_arg_1();
+	Cpu_state &cpu_state = *(Cpu_state*)user_arg_2();
+	static_cast<Cpu_state&>(*thread.regs) = cpu_state;
+}
+
+
+void Thread::_call_exception_state() {
+	Thread &thread = *(Thread*)user_arg_1();
+	Exception_state &exception_state = *(Exception_state*)user_arg_2();
+	exception_state = thread.exception_state();
+}
+
+
+void Thread::_call_single_step() {
+	Thread &thread = *(Thread*)user_arg_1();
+	bool on = *(bool*)user_arg_2();
+	Cpu::single_step(*thread.regs, on);
+}
+
+
 void Thread::_call()
 {
 	try {
@@ -871,6 +900,10 @@ void Thread::_call()
 	case call_id_new_obj():                _call_new_obj(); return;
 	case call_id_delete_obj():             _call_delete_obj(); return;
 	case call_id_suspend():                _call_suspend(); return;
+	case call_id_get_cpu_state():          _call_get_cpu_state(); return;
+	case call_id_set_cpu_state():          _call_set_cpu_state(); return;
+	case call_id_exception_state():        _call_exception_state(); return;
+	case call_id_single_step():            _call_single_step(); return;
 	default:
 		Genode::raw(*this, ": unknown kernel call");
 		_die();
@@ -883,6 +916,7 @@ void Thread::_call()
 void Thread::_mmu_exception()
 {
 	_become_inactive(AWAITS_RESTART);
+	_exception_state = MMU_FAULT;
 	Cpu::mmu_fault(*regs, _fault);
 	_fault.ip = regs->ip;
 
@@ -901,6 +935,25 @@ void Thread::_mmu_exception()
 }
 
 
+void Thread::_exception()
+{
+	_become_inactive(AWAITS_RESTART);
+	_exception_state = EXCEPTION;
+
+	if (_type != USER) {
+		Genode::raw(*this, " raised an exception, which should never happen");
+		_die();
+	}
+
+	if (_pager && _pager->can_submit(1)) {
+		_pager->submit(1);
+	} else {
+		Genode::raw(*this, " could not send signal to pager on exception");
+		_die();
+	}
+}
+
+
 Thread::Thread(Board::Address_space_id_allocator &addr_space_id_alloc,
                Irq::Pool                         &user_irq_pool,
                Cpu_pool                          &cpu_pool,

repos/base-hw/src/core/kernel/thread.h

@@ -59,6 +59,8 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 
 		enum Type { USER, CORE, IDLE };
 
+		enum Exception_state { NO_EXCEPTION, MMU_FAULT, EXCEPTION };
+
 	private:
 
 		/*
@@ -181,6 +183,7 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 		bool                               _paused                   { false };
 		bool                               _cancel_next_await_signal { false };
 		Type const                         _type;
+		Exception_state                    _exception_state          { NO_EXCEPTION };
 
 		Genode::Constructible<Tlb_invalidation>   _tlb_invalidation {};
 		Genode::Constructible<Destroy>            _destroy {};
@@ -233,6 +236,11 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 		 */
 		void _mmu_exception();
 
+		/**
+		 * Handle a non-mmu exception
+		 */
+		void _exception();
+
 		/**
 		 * Handle kernel-call request of the thread
 		 */
@@ -294,6 +302,10 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 		void _call_timeout_max_us();
 		void _call_time();
 		void _call_suspend();
+		void _call_get_cpu_state();
+		void _call_set_cpu_state();
+		void _call_exception_state();
+		void _call_single_step();
 
 		template <typename T, typename... ARGS>
 		void _call_new(ARGS &&... args)
@@ -468,6 +480,7 @@ class Kernel::Thread : private Kernel::Object, public Cpu_job, private Timeout
 		Thread_fault fault() const { return _fault; }
 		Genode::Native_utcb *utcb() { return _utcb; }
 		Type type() const { return _type; }
+		Exception_state exception_state() const { return _exception_state; }
 
 		Pd &pd() const
 		{

repos/base-hw/src/core/pager.cc

@@ -61,9 +61,6 @@ void Pager_object::start_paging(Kernel_object<Kernel::Signal_receiver> & receive
 }
 
 
-void Pager_object::exception_handler(Signal_context_capability) { }
-
-
 void Pager_object::unresolved_page_fault_occurred() { }
 
 

repos/base-hw/src/core/pager.h

@@ -105,6 +105,12 @@ class Core::Pager_object : private Object_pool<Pager_object>::Entry,
 		Cpu_session_capability _cpu_session_cap;
 		Thread_capability      _thread_cap;
 
+		/**
+		 * User-level signal handler registered for this pager object via
+		 * 'Cpu_session::exception_handler()'.
+		 */
+		Signal_context_capability _exception_sigh { };
+
 	public:
 
 		/**
@@ -128,9 +134,24 @@ class Core::Pager_object : private Object_pool<Pager_object>::Entry,
 		void wake_up();
 
 		/**
-		 * Unnecessary as base-hw doesn't use exception handlers
+		 * Assign user-level exception handler for the pager object
 		 */
-		void exception_handler(Signal_context_capability);
+		void exception_handler(Signal_context_capability sigh)
+		{
+			_exception_sigh = sigh;
+		}
+
+		/**
+		 * Notify exception handler about the occurrence of an exception
+		 */
+		bool submit_exception_signal()
+		{
+			if (!_exception_sigh.valid()) return false;
+
+			Signal_transmitter transmitter(_exception_sigh);
+			transmitter.submit();
+			return true;
+		}
 
 		/**
 		 * Install information that is necessary to handle page faults

repos/base-hw/src/core/platform_thread.cc

@@ -210,15 +210,31 @@ Core::Pager_object &Platform_thread::pager()
 
 Thread_state Platform_thread::state()
 {
-	Thread_state bstate(*_kobj->regs);
-	return Thread_state(bstate);
+	Cpu_state cpu_state;
+	Kernel::get_cpu_state(*_kobj, cpu_state);
+	Thread_state state(cpu_state);
+
+	using Exception_state = Kernel::Thread::Exception_state;
+
+	switch (exception_state()) {
+	case Exception_state::NO_EXCEPTION:
+		break;
+	case Exception_state::MMU_FAULT:
+		state.unresolved_page_fault = true;
+		break;
+	case Exception_state::EXCEPTION:
+		state.exception = true;
+		break;
+	}
+
+	return state;
 }
 
 
 void Platform_thread::state(Thread_state thread_state)
 {
-	Cpu_state * cstate = static_cast<Cpu_state *>(&*_kobj->regs);
-	*cstate = static_cast<Cpu_state>(thread_state);
+	Cpu_state cpu_state(thread_state);
+	Kernel::set_cpu_state(*_kobj, cpu_state);
 }
 
 

repos/base-hw/src/core/platform_thread.h

@@ -124,6 +124,22 @@ class Core::Platform_thread : Noncopyable
 		 */
 		~Platform_thread();
 
+		/**
+		 * Return information about current exception state
+		 *
+		 * This syscall wrapper is located here and not in
+		 * 'core_interface.h' because the 'Thread::Exception_state'
+		 * type is not known there.
+		 */
+		Kernel::Thread::Exception_state exception_state()
+		{
+			Kernel::Thread::Exception_state exception_state;
+			using namespace Kernel;
+			call(call_id_exception_state(), (Call_arg)&*_kobj,
+			                                (Call_arg)&exception_state);
+			return exception_state;
+		}
+
 		/**
 		 * Return information about current fault
 		 */
@@ -158,12 +174,19 @@ class Core::Platform_thread : Noncopyable
 		/**
 		 * Enable/disable single stepping
 		 */
-		void single_step(bool) { }
+		void single_step(bool on) { Kernel::single_step(*_kobj, on); }
 
 		/**
 		 * Resume this thread
 		 */
-		void resume() { Kernel::resume_thread(*_kobj); }
+		void resume()
+		{
+			if (exception_state() !=
+			    Kernel::Thread::Exception_state::NO_EXCEPTION)
+				restart();
+
+			Kernel::resume_thread(*_kobj);
+		}
 
 		/**
 		 * Set CPU quota of the thread to 'quota'

repos/base-hw/src/core/region_map_support.cc

@@ -43,6 +43,16 @@ void Pager_entrypoint::entry()
 			continue;
 		}
 
+		if (pt->exception_state() ==
+		    Kernel::Thread::Exception_state::EXCEPTION) {
+			if (!po->submit_exception_signal())
+				warning("unresolvable exception: "
+				        "pd='",     pt->pd()->label(), "', "
+				        "thread='", pt->label(),       "', "
+				        "ip=",      Hex(pt->state().ip));
+			continue;
+		}
+
 		_fault = pt->fault_info();
 
 		/* try to resolve fault directly via local region managers */

repos/base-hw/src/core/spec/arm/cpu_support.h

@@ -120,6 +120,8 @@ struct Core::Arm_cpu : public Hw::Arm_cpu
 	 * Return kernel name of the executing CPU
 	 */
 	static unsigned executing_id() { return 0; }
+
+	static void single_step(Context &, bool) { };
 };
 
 #endif /* _CORE__SPEC__ARM__CPU_SUPPORT_H_ */

repos/base-hw/src/core/spec/arm_v8/cpu.h

@@ -75,6 +75,7 @@ struct Core::Cpu : Hw::Arm_64_cpu
 	struct alignas(16) Context : Cpu_state
 	{
 		uint64_t  pstate { };
+		uint64_t  mdscr_el1 { };
 		uint64_t  exception_type { RESET };
 		Fpu_state fpu_state { };
 
@@ -104,6 +105,12 @@ struct Core::Cpu : Hw::Arm_64_cpu
 
 	static void mmu_fault(Context &, Kernel::Thread_fault &);
 
+	static void single_step(Context &regs, bool on)
+	{
+		Cpu::Spsr::Ss::set(regs.pstate, on ? 1 : 0);
+		Cpu::Mdscr::Ss::set(regs.mdscr_el1, on ? 1 : 0);
+	};
+
 	/**
 	 * Return kernel name of the executing CPU
 	 */

repos/base-hw/src/core/spec/arm_v8/exception_vector.s

@@ -35,10 +35,12 @@
 	mrs  x1, sp_el0
 	mrs  x2, elr_el1
 	mrs  x3, spsr_el1
-	adr  x4, .
-	and  x4, x4, #0xf80
+	mrs  x4, mdscr_el1
+	adr  x5, .
+	and  x5, x5, #0xf80
 	stp  x1, x2, [x0], #16
-	stp  x3, x4, [x0], #16
+	stp  xzr, x3, [x0], #16   /* ec will be updated later if needed */
+	stp  x4, x5, [x0], #16
 	b _kernel_entry
 	.balign 128
 	.endr
@@ -91,11 +93,12 @@ _kernel_entry:
 	mov  sp, x1               /* reset stack */
 	str  x0, [sp, #-16]       /* store cpu state pointer */
 	add  x1, x0, #8*31
-	ldp  x2, x3, [x1], #16    /* load sp, ip */
-	ldr  x4, [x1], #16        /* load pstate */
+	ldp  x2, x3, [x1], #16+8  /* load sp, ip, skip ec */
+	ldp  x4, x5, [x1], #16+8  /* load pstate, mdscr_el1, skip exception_type */
 	msr  sp_el0,   x2
 	msr  elr_el1,  x3
 	msr  spsr_el1, x4
+	msr  mdscr_el1, x5
 	ldp  q0,  q1,  [x1], #32
 	ldp  q2,  q3,  [x1], #32
 	ldp  q4,  q5,  [x1], #32

repos/base-hw/src/core/spec/arm_v8/kernel/thread.cc

@@ -53,6 +53,11 @@ void Thread::exception(Cpu & cpu)
 			case Cpu::Esr::Ec::DATA_ABORT_LOW_LEVEL:
 				_mmu_exception();
 				return;
+			case Cpu::Esr::Ec::SOFTWARE_STEP_LOW_LEVEL: [[fallthrough]];
+			case Cpu::Esr::Ec::BRK:
+				regs->ec = Cpu::Esr::Ec::get(esr);
+				_exception();
+				return;
 			default:
 				Genode::raw("Unknown cpu exception EC=", Cpu::Esr::Ec::get(esr),
 				            " ISS=", Cpu::Esr::Iss::get(esr),

repos/base-hw/src/core/spec/riscv/cpu.h

@@ -101,6 +101,8 @@ class Core::Cpu : public Hw::Riscv_cpu
 		void switch_to(Mmu_context & context);
 		static void mmu_fault(Context & c, Kernel::Thread_fault & f);
 
+		static void single_step(Context &, bool) { };
+
 		static unsigned executing_id() { return 0; }
 
 		static void clear_memory_region(addr_t const addr,

repos/base-hw/src/core/spec/x86_64/cpu.cc

@@ -158,3 +158,12 @@ void Cpu::clear_memory_region(addr_t const addr, size_t const size, bool)
 		memset((void*)addr, 0, size);
 	}
 }
+
+
+void Cpu::single_step(Context &regs, bool on)
+{
+	if (on)
+		regs.eflags |= Context::Eflags::EFLAGS_TF;
+	else
+		regs.eflags &= ~Context::Eflags::EFLAGS_TF;
+}

repos/base-hw/src/core/spec/x86_64/cpu.h

@@ -101,6 +101,7 @@ class Core::Cpu : public Hw::X86_64_cpu
 		struct alignas(16) Context : Cpu_state, Kernel_stack, Fpu_context
 		{
 			enum Eflags {
+				EFLAGS_TF     = 1 << 8,
 				EFLAGS_IF_SET = 1 << 9,
 				EFLAGS_IOPL_3 = 3 << 12,
 			};
@@ -134,6 +135,8 @@ class Core::Cpu : public Hw::X86_64_cpu
 
 		static void mmu_fault(Context & regs, Kernel::Thread_fault & fault);
 
+		static void single_step(Context &regs, bool on);
+
 		/**
 		 * Invalidate the whole TLB
 		 */

repos/base-hw/src/core/spec/x86_64/exception_vector.s

@@ -147,9 +147,19 @@
 	.align 8
 	__idt:
 
-	/* first 128 entries */
+	/* first 3 entries */
 	.set isr_addr, ISR
-	.rept 0x80
+	.rept 3
+	_idt_entry isr_addr IDT_FLAGS_PRIVILEGED
+	.set isr_addr, isr_addr + ISR_ENTRY_SIZE
+	.endr
+
+	/* int3 */
+	_idt_entry isr_addr IDT_FLAGS_UNPRIVILEGED
+	.set isr_addr, isr_addr + ISR_ENTRY_SIZE
+
+	/* entries 4-127 */
+	.rept 124
 	_idt_entry isr_addr IDT_FLAGS_PRIVILEGED
 	.set isr_addr, isr_addr + ISR_ENTRY_SIZE
 	.endr

repos/base-hw/src/core/spec/x86_64/kernel/thread_exception.cc

@@ -30,9 +30,12 @@ void Thread::exception(Cpu & cpu)
 		_mmu_exception();
 		return;
 
+	case Cpu_state::DIVIDE_ERROR:
+	case Cpu_state::DEBUG:
+	case Cpu_state::BREAKPOINT:
 	case Cpu_state::UNDEFINED_INSTRUCTION:
-		Genode::raw(*this, ": undefined instruction at ip=", (void*)regs->ip);
-		_die();
+	case Cpu_state::GENERAL_PROTECTION:
+		_exception();
 		return;
 
 	case Cpu_state::SUPERVISOR_CALL:

repos/base-hw/src/include/hw/spec/arm_64/cpu.h

@@ -84,6 +84,8 @@ struct Hw::Arm_64_cpu
 				INST_ABORT_SAME_LEVEL   = 0b100001,
 				DATA_ABORT_LOW_LEVEL    = 0b100100,
 				DATA_ABORT_SAME_LEVEL   = 0b100101,
+				SOFTWARE_STEP_LOW_LEVEL = 0b110010,
+				BRK                     = 0b111100,
 			};
 		};
 
@@ -144,6 +146,11 @@ struct Hw::Arm_64_cpu
 	SYSTEM_REGISTER(64, Mair_el1, mair_el1);
 	SYSTEM_REGISTER(64, Mair_el2, mair_el2);
 
+	struct Mdscr : Genode::Register<64>
+	{
+		struct Ss  : Bitfield<0,  1> {};
+	};
+
 	SYSTEM_REGISTER(64, Mpidr, mpidr_el1,
 		struct Aff0 : Bitfield<0,  8> {};
 		struct Aff1 : Bitfield<8,  8> {};
@@ -185,6 +192,7 @@ struct Hw::Arm_64_cpu
 		struct I  : Bitfield<7,  1> {};
 		struct A  : Bitfield<8,  1> {};
 		struct D  : Bitfield<9,  1> {};
+		struct Ss : Bitfield<21, 1> {};
 	};
 
 	SYSTEM_REGISTER(64, Spsr_el2, spsr_el2);

repos/base/include/spec/arm_64/cpu/cpu_state.h

@@ -22,9 +22,15 @@ namespace Genode { struct Cpu_state; }
 
 struct Genode::Cpu_state
 {
+	enum Cpu_exception {
+		SOFTWARE_STEP = 0x32,
+		BREAKPOINT    = 0x3c,
+	};
+
 	addr_t r[31] { 0 }; /* general purpose register 0...30 */
 	addr_t sp    { 0 }; /* stack pointer                   */
 	addr_t ip    { 0 }; /* instruction pointer             */
+	addr_t ec    { 0 }; /* exception class                 */
 };
 
 #endif /* _INCLUDE__SPEC__ARM_64__CPU__CPU_STATE_H_ */