xref: /glibc-2.36/hurd/hurd/signal.h

/* Implementing POSIX.1 signals under the Hurd.
   Copyright (C) 1993-2022 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef	_HURD_SIGNAL_H

#define	_HURD_SIGNAL_H	1
#include <features.h>

#define __need_size_t
#define __need_NULL
#include <stddef.h>

#include <mach/mach_types.h>
#include <mach/port.h>
#include <mach/message.h>
#include <hurd/hurd_types.h>
#include <signal.h>
#include <errno.h>
#include <bits/types/error_t.h>
#include <bits/types/stack_t.h>
#include <bits/types/sigset_t.h>
#include <bits/sigaction.h>
#include <hurd/msg.h>

#include <setjmp.h>		/* For `jmp_buf'.  */
#include <spin-lock.h>
struct hurd_signal_preemptor;	/* <hurd/sigpreempt.h> */
#if defined __USE_EXTERN_INLINES && defined _LIBC
# if IS_IN (libc) || IS_IN (libpthread)
#  include <sigsetops.h>
# endif
#endif


/* Full details of a signal.  */
struct hurd_signal_detail
  {
    /* Codes from origination Mach exception_raise message.  */
    integer_t exc, exc_code, exc_subcode;
    /* Sigcode as passed or computed from exception codes.  */
    integer_t code;
    /* Error code as passed or extracted from exception codes.  */
    error_t error;
  };


/* Per-thread signal state.  */

struct hurd_sigstate
  {
    spin_lock_t critical_section_lock; /* Held if in critical section.  */

    spin_lock_t lock;		/* Locks most of the rest of the structure.  */

    /* The signal state holds a reference on the thread port.  */
    thread_t thread;

    struct hurd_sigstate *next; /* Linked-list of thread sigstates.  */

    sigset_t blocked;		/* What signals are blocked.  */
    sigset_t pending;		/* Pending signals, possibly blocked.  */

    /* Signal handlers.  ACTIONS[0] is used to mark the threads with POSIX
       semantics: if sa_handler is SIG_IGN instead of SIG_DFL, this thread
       will receive global signals and use the process-wide action vector
       instead of this one.  */
    struct sigaction actions[_NSIG];

    stack_t sigaltstack;

    /* Chain of thread-local signal preemptors; see <hurd/sigpreempt.h>.
       Each element of this chain is in local stack storage, and the chain
       parallels the stack: the head of this chain is in the innermost
       stack frame, and each next element in an outermore frame.  */
    struct hurd_signal_preemptor *preemptors;

    /* For each signal that may be pending, the details to deliver it with.  */
    struct hurd_signal_detail pending_data[_NSIG];

    /* If `suspended' is set when this thread gets a signal,
       the signal thread sends an empty message to it.  */
    mach_port_t suspended;

    /* The following members are not locked.  They are used only by this
       thread, or by the signal thread with this thread suspended.  */

    volatile mach_port_t intr_port; /* Port interruptible RPC was sent on.  */

    /* If this is not null, the thread is in sigreturn awaiting delivery of
       pending signals.  This context (the machine-dependent portions only)
       will be passed to sigreturn after running the handler for a pending
       signal, instead of examining the thread state.  */
    struct sigcontext *context;

    /* This is the head of the thread's list of active resources; see
       <hurd/userlink.h> for details.  This member is only used by the
       thread itself, and always inside a critical section.  */
    struct hurd_userlink *active_resources;

    /* These are locked normally.  */
    int cancel;			/* Flag set by hurd_thread_cancel.  */
    void (*cancel_hook) (void);	/* Called on cancellation.  */
  };

/* Linked list of states of all threads whose state has been asked for.  */

extern struct hurd_sigstate *_hurd_sigstates;

/* Get the sigstate of a given thread.  If there was no sigstate for
   the thread, one is created, and the thread gains a reference.  If
   the given thread is MACH_PORT_NULL, return the global sigstate.  */

extern struct hurd_sigstate *_hurd_thread_sigstate (thread_t);

/* Get the sigstate of the current thread.
   This uses a per-thread variable to optimize the lookup.  */

extern struct hurd_sigstate *_hurd_self_sigstate (void)
     /* This declaration tells the compiler that the value is constant.
	We assume this won't be called twice from the same stack frame
	by different threads.  */
     __attribute__ ((__const__));

/* Process-wide signal state.  */

extern struct hurd_sigstate *_hurd_global_sigstate;

/* Mark the given thread as a process-wide signal receiver.  */

extern void _hurd_sigstate_set_global_rcv (struct hurd_sigstate *ss);

/* A thread can either use its own action vector and pending signal set
   or use the global ones, depending on wether it has been marked as a
   global receiver. The accessors below take that into account.  */

extern void _hurd_sigstate_lock (struct hurd_sigstate *ss);
extern struct sigaction *_hurd_sigstate_actions (struct hurd_sigstate *ss);
extern sigset_t _hurd_sigstate_pending (const struct hurd_sigstate *ss);
extern void _hurd_sigstate_unlock (struct hurd_sigstate *ss);

/* Used by libpthread to remove stale sigstate structures.  */
extern void _hurd_sigstate_delete (thread_t thread);

#ifndef _HURD_SIGNAL_H_EXTERN_INLINE
#define _HURD_SIGNAL_H_EXTERN_INLINE __extern_inline
#endif

#if defined __USE_EXTERN_INLINES && defined _LIBC
# if IS_IN (libc)
_HURD_SIGNAL_H_EXTERN_INLINE struct hurd_sigstate *
_hurd_self_sigstate (void)
{
  if (THREAD_GETMEM (THREAD_SELF, _hurd_sigstate) == NULL)
    {
      thread_t self = __mach_thread_self ();
      THREAD_SETMEM (THREAD_SELF, _hurd_sigstate, _hurd_thread_sigstate (self));
      __mach_port_deallocate (__mach_task_self (), self);
    }
  return THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
}
# endif
#endif

/* Thread listening on our message port; also called the "signal thread".  */

extern thread_t _hurd_msgport_thread;

/* Our message port.  We hold the receive right and _hurd_msgport_thread
   listens for messages on it.  We also hold a send right, for convenience.  */

extern mach_port_t _hurd_msgport;

/* Resource limit on core file size.  Enforced by hurdsig.c.  */
extern int _hurd_core_limit;

/* Critical sections.

   A critical section is a section of code which cannot safely be interrupted
   to run a signal handler; for example, code that holds any lock cannot be
   interrupted lest the signal handler try to take the same lock and
   deadlock result.

   As a consequence, a critical section will see its RPCs return EINTR, even if
   SA_RESTART is set!  In that case, the critical section should be left, so
   that the handler can run, and the whole critical section be tried again, to
   avoid unexpectingly exposing EINTR to the application.  */

extern void *_hurd_critical_section_lock (void);

#if defined __USE_EXTERN_INLINES && defined _LIBC
# if IS_IN (libc)
_HURD_SIGNAL_H_EXTERN_INLINE void *
_hurd_critical_section_lock (void)
{
  struct hurd_sigstate *ss;

#ifdef __LIBC_NO_TLS
  if (__LIBC_NO_TLS ())
    /* TLS is currently initializing, no need to enter critical section.  */
    return NULL;
#endif

  ss = THREAD_GETMEM (THREAD_SELF, _hurd_sigstate);
  if (ss == NULL)
    {
      thread_t self = __mach_thread_self ();

      /* The thread variable is unset; this must be the first time we've
	 asked for it.  In this case, the critical section flag cannot
	 possible already be set.  Look up our sigstate structure the slow
	 way.  */
      ss = _hurd_thread_sigstate (self);
      THREAD_SETMEM (THREAD_SELF, _hurd_sigstate, ss);
      __mach_port_deallocate (__mach_task_self (), self);
    }

  if (! __spin_try_lock (&ss->critical_section_lock))
    /* We are already in a critical section, so do nothing.  */
    return NULL;

  /* With the critical section lock held no signal handler will run.
     Return our sigstate pointer; this will be passed to
     _hurd_critical_section_unlock to unlock it.  */
  return ss;
}
# endif
#endif

extern void _hurd_critical_section_unlock (void *our_lock);

#if defined __USE_EXTERN_INLINES && defined _LIBC
# if IS_IN (libc)
_HURD_SIGNAL_H_EXTERN_INLINE void
_hurd_critical_section_unlock (void *our_lock)
{
  if (our_lock == NULL)
    /* The critical section lock was held when we began.  Do nothing.  */
    return;
  else
    {
      /* It was us who acquired the critical section lock.  Unlock it.  */
      struct hurd_sigstate *ss = (struct hurd_sigstate *) our_lock;
      sigset_t pending;
      _hurd_sigstate_lock (ss);
      __spin_unlock (&ss->critical_section_lock);
      pending = _hurd_sigstate_pending(ss) & ~ss->blocked;
      _hurd_sigstate_unlock (ss);
      if (! __sigisemptyset (&pending))
	/* There are unblocked signals pending, which weren't
	   delivered because we were in the critical section.
	   Tell the signal thread to deliver them now.  */
	__msg_sig_post (_hurd_msgport, 0, 0, __mach_task_self ());
    }
}
# endif
#endif

/* Convenient macros for simple uses of critical sections.
   These two must be used as a pair at the same C scoping level.  */

#define HURD_CRITICAL_BEGIN \
  { void *__hurd_critical__ = _hurd_critical_section_lock ()
#define HURD_CRITICAL_END \
      _hurd_critical_section_unlock (__hurd_critical__); } while (0)

/* This one can be used inside the C scoping level, for early exits.  */
#define HURD_CRITICAL_UNLOCK \
      _hurd_critical_section_unlock (__hurd_critical__);

/* Initialize the signal code, and start the signal thread.
   Arguments give the "init ints" from exec_startup.  */

extern void _hurdsig_init (const int *intarray, size_t intarraysize);

/* Initialize proc server-assisted fault recovery for the signal thread.  */

extern void _hurdsig_fault_init (void);

/* Raise a signal as described by SIGNO an DETAIL, on the thread whose
   sigstate SS points to.  If SS is a null pointer, this instead affects
   the calling thread.  */

extern int _hurd_raise_signal (struct hurd_sigstate *ss, int signo,
			       const struct hurd_signal_detail *detail);

/* Translate a Mach exception into a signal (machine-dependent).  */

extern void _hurd_exception2signal (struct hurd_signal_detail *detail,
				    int *signo);

/* Translate a Mach exception into a signal with a legacy sigcode.  */

extern void _hurd_exception2signal_legacy (struct hurd_signal_detail *detail,
					   int *signo);


/* Make the thread described by SS take the signal described by SIGNO and
   DETAIL.  If the process is traced, this will in fact stop with a SIGNO
   as the stop signal unless UNTRACED is nonzero.  When the signal can be
   considered delivered, sends a sig_post reply message on REPLY_PORT
   indicating success.  SS is not locked.  */

extern void _hurd_internal_post_signal (struct hurd_sigstate *ss,
					int signo,
					struct hurd_signal_detail *detail,
					mach_port_t reply_port,
					mach_msg_type_name_t reply_port_type,
					int untraced);

/* Set up STATE and SS to handle signal SIGNO by running HANDLER.  If
   RPC_WAIT is nonzero, the thread needs to wait for a pending RPC to
   finish before running the signal handler.  The handler is passed SIGNO,
   SIGCODE, and the returned `struct sigcontext' (which resides on the
   stack the handler will use, and which describes the state of the thread
   encoded in STATE before running the handler).  */

struct machine_thread_all_state;
extern struct sigcontext *
_hurd_setup_sighandler (struct hurd_sigstate *ss, const struct sigaction *action,
			__sighandler_t handler,
			int signo, struct hurd_signal_detail *detail,
			int rpc_wait, struct machine_thread_all_state *state);

/* Function run by the signal thread to receive from the signal port.  */

extern void *_hurd_msgport_receive (void *arg);

/* Set up STATE with a thread state that, when resumed, is
   like `longjmp (_hurd_sigthread_fault_env, 1)'.  */

extern void _hurd_initialize_fault_recovery_state (void *state);

/* Set up STATE to do the equivalent of `longjmp (ENV, VAL);'.  */

extern void _hurd_longjmp_thread_state (void *state, jmp_buf env, int value);

/* Function run for SIGINFO when its action is SIG_DFL and the current
   process is the session leader.  */

extern void _hurd_siginfo_handler (int);

/* Replacement for mach_msg used in RPCs to provide Hurd interruption
   semantics.  Args are all the same as for mach_msg.  intr-rpc.h arranges
   for this version to be used automatically by the RPC stubs the library
   builds in place of the normal mach_msg. */
error_t _hurd_intr_rpc_mach_msg (mach_msg_header_t *msg,
				 mach_msg_option_t option,
				 mach_msg_size_t send_size,
				 mach_msg_size_t rcv_size,
				 mach_port_t rcv_name,
				 mach_msg_timeout_t timeout,
				 mach_port_t notify);


/* Milliseconds to wait for an interruptible RPC to return after
   `interrupt_operation'.  */

extern mach_msg_timeout_t _hurd_interrupted_rpc_timeout;


/* Mask of signals that cannot be caught, blocked, or ignored.  */
#define	_SIG_CANT_MASK	(__sigmask (SIGSTOP) | __sigmask (SIGKILL))

/* Do an RPC to a process's message port.

   Each argument is an expression which returns an error code; each
   expression may be evaluated several times.  FETCH_MSGPORT_EXPR should
   fetch the appropriate message port and store it in the local variable
   `msgport'; it will be deallocated after use.  FETCH_REFPORT_EXPR should
   fetch the appropriate message port and store it in the local variable
   `refport' (if no reference port is needed in the call, then
   FETCH_REFPORT_EXPR should be simply KERN_SUCCESS or 0); if
   DEALLOC_REFPORT evaluates to nonzero it will be deallocated after use,
   otherwise the FETCH_REFPORT_EXPR must take care of user references to
   `refport'.  RPC_EXPR should perform the desired RPC operation using
   `msgport' and `refport'.

   The reason for the complexity is that a process's message port and
   reference port may change between fetching those ports and completing an
   RPC using them (usually they change only when a process execs).  The RPC
   will fail with MACH_SEND_INVALID_DEST if the msgport dies before we can
   send the RPC request; or with MIG_SERVER_DIED if the msgport was
   destroyed after we sent the RPC request but before it was serviced.  In
   either of these cases, we retry the entire operation, discarding the old
   message and reference ports and fetch them anew.  */

#define HURD_MSGPORT_RPC(fetch_msgport_expr,				      \
			 fetch_refport_expr, dealloc_refport,		      \
			 rpc_expr) 					      \
({									      \
    error_t __err;							      \
    mach_port_t msgport, refport = MACH_PORT_NULL;			      \
    do									      \
      {									      \
	/* Get the message port.  */					      \
	__err = (error_t) (fetch_msgport_expr);				      \
	if (__err)							      \
	  break;							      \
	/* Get the reference port.  */					      \
	__err = (error_t) (fetch_refport_expr);				      \
	if (__err)							      \
	  {								      \
	    /* Couldn't get it; deallocate MSGPORT and fail.  */	      \
	    __mach_port_deallocate (__mach_task_self (), msgport);	      \
	    break;							      \
	  }								      \
	__err = (error_t) (rpc_expr);					      \
	__mach_port_deallocate (__mach_task_self (), msgport);		      \
	if ((dealloc_refport) && refport != MACH_PORT_NULL)		      \
	  __mach_port_deallocate (__mach_task_self (), refport);    	      \
      } while (__err == MACH_SEND_INVALID_DEST				      \
	       || __err == MIG_SERVER_DIED);				      \
    __err;								      \
})


#endif	/* hurd/signal.h */