Kernel: Move signal handlers from being thread state to process state

POSIX requires that sigaction() and friends set a _process-wide_ signal
handler, so move signal handlers and flags inside Process.
This also fixes a "pid/tid confusion" FIXME, as we can now send the
signal to the process and let that decide which thread should get the
signal (which is the thread with tid==pid, but that's now the Process's
problem).
Note that each thread still retains its signal mask, as that is local to
each thread.

Kernel/Process.cpp

@@ -612,10 +612,9 @@ void Process::finalize()
  m_state.store(State::Dead, AK::MemoryOrder::memory_order_release);
 
  {
- // FIXME: PID/TID BUG
- if (auto parent_thread = Thread::from_tid(ppid().value())) {
- if (parent_thread->process().is_user_process() && (parent_thread->m_signal_action_data[SIGCHLD].flags & SA_NOCLDWAIT) != SA_NOCLDWAIT)
- parent_thread->send_signal(SIGCHLD, this);
+ if (auto parent_process = Process::from_pid(ppid())) {
+ if (parent_process->is_user_process() && (parent_process->m_signal_action_data[SIGCHLD].flags & SA_NOCLDWAIT) != SA_NOCLDWAIT)
+ (void)parent_process->send_signal(SIGCHLD, this);
  }
  }
 

Kernel/Process.h

@@ -827,6 +827,12 @@ class Process final
  NonnullRefPtrVector<Thread> m_threads_for_coredump;
 
  mutable RefPtr<ProcessProcFSTraits> m_procfs_traits;
+ struct SignalActionData {
+ VirtualAddress handler_or_sigaction;
+ int flags { 0 };
+ u32 mask { 0 };
+ };
+ Array<SignalActionData, NSIG> m_signal_action_data;
 
  static_assert(sizeof(ProtectedValues) < (PAGE_SIZE));
  alignas(4096) ProtectedValues m_protected_values;

Kernel/Syscalls/sigaction.cpp

@@ -58,15 +58,17 @@ ErrorOr<FlatPtr> Process::sys$sigaction(int signum, Userspace<const sigaction*>
  return EINVAL;
 
  InterruptDisabler disabler; // FIXME: This should use a narrower lock. Maybe a way to ignore signals temporarily?
- auto& action = Thread::current()->m_signal_action_data[signum];
+ auto& action = m_signal_action_data[signum];
  if (user_old_act) {
  sigaction old_act {};
  old_act.sa_flags = action.flags;
  old_act.sa_sigaction = reinterpret_cast<decltype(old_act.sa_sigaction)>(action.handler_or_sigaction.as_ptr());
+ old_act.sa_mask = action.mask;
  TRY(copy_to_user(user_old_act, &old_act));
  }
  if (user_act) {
  auto act = TRY(copy_typed_from_user(user_act));
+ action.mask = act.sa_mask;
  action.flags = act.sa_flags;
  action.handler_or_sigaction = VirtualAddress { reinterpret_cast<void*>(act.sa_sigaction) };
  }

Kernel/Thread.cpp

@@ -790,7 +790,7 @@ void Thread::reset_signals_for_exec()
  // The signal mask is preserved across execve(2).
  // The pending signal set is preserved across an execve(2).
  m_have_any_unmasked_pending_signals.store(false, AK::memory_order_release);
- m_signal_action_data.fill({});
+ m_signal_action_masks.fill({});
  // A successful call to execve(2) removes any existing alternate signal stack
  m_alternative_signal_stack = 0;
  m_alternative_signal_stack_size = 0;
@@ -902,7 +902,7 @@ static DefaultSignalAction default_signal_action(u8 signal)
 bool Thread::should_ignore_signal(u8 signal) const
 {
  VERIFY(signal < 32);
- auto const& action = m_signal_action_data[signal];
+ auto const& action = m_process->m_signal_action_data[signal];
  if (action.handler_or_sigaction.is_null())
  return default_signal_action(signal) == DefaultSignalAction::Ignore;
  return ((sighandler_t)action.handler_or_sigaction.get() == SIG_IGN);
@@ -911,7 +911,7 @@ bool Thread::should_ignore_signal(u8 signal) const
 bool Thread::has_signal_handler(u8 signal) const
 {
  VERIFY(signal < 32);
- auto const& action = m_signal_action_data[signal];
+ auto const& action = m_process->m_signal_action_data[signal];
  return !action.handler_or_sigaction.is_null();
 }
 
@@ -975,7 +975,7 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
  return DispatchSignalResult::Deferred;
  }
 
- auto& action = m_signal_action_data[signal];
+ auto& action = m_process->m_signal_action_data[signal];
  // FIXME: Implement SA_SIGINFO signal handlers.
  VERIFY(!(action.flags & SA_SIGINFO));
 
@@ -1045,7 +1045,7 @@ DispatchSignalResult Thread::dispatch_signal(u8 signal)
  ScopedAddressSpaceSwitcher switcher(m_process);
 
  u32 old_signal_mask = m_signal_mask;
- u32 new_signal_mask = action.mask;
+ u32 new_signal_mask = m_signal_action_masks[signal].value_or(action.mask);
  if ((action.flags & SA_NODEFER) == SA_NODEFER)
  new_signal_mask &= ~(1 << (signal - 1));
  else
@@ -1182,8 +1182,7 @@ RegisterState& Thread::get_register_dump_from_stack()
 ErrorOr<NonnullRefPtr<Thread>> Thread::try_clone(Process& process)
 {
  auto clone = TRY(Thread::try_create(process));
- auto signal_action_data_span = m_signal_action_data.span();
- signal_action_data_span.copy_to(clone->m_signal_action_data.span());
+ m_signal_action_masks.span().copy_to(clone->m_signal_action_masks);
  clone->m_signal_mask = m_signal_mask;
  clone->m_fpu_state = m_fpu_state;
  clone->m_thread_specific_data = m_thread_specific_data;

Kernel/Thread.h

@@ -46,12 +46,6 @@ enum class DispatchSignalResult {
  Continue
 };
 
-struct SignalActionData {
- VirtualAddress handler_or_sigaction;
- u32 mask { 0 };
- int flags { 0 };
-};
-
 struct ThreadSpecificData {
  ThreadSpecificData* self;
 };
@@ -1225,7 +1219,7 @@ class Thread
  NonnullOwnPtr<Memory::Region> m_kernel_stack_region;
  VirtualAddress m_thread_specific_data;
  Optional<Memory::VirtualRange> m_thread_specific_range;
- Array<SignalActionData, NSIG> m_signal_action_data;
+ Array<Optional<u32>, NSIG> m_signal_action_masks;
  Blocker* m_blocker { nullptr };
  Kernel::Mutex* m_blocking_mutex { nullptr };
  u32 m_lock_requested_count { 0 };