Provide ABI modules hooks for process exec/exit and thread exit.

Exec and exit are same as corresponding eventhandler hooks.

Thread exit hook is called somewhat earlier, while thread is still
owned by the process and enough context is available.  Note that the
process lock is owned when the hook is called.

Reviewed by:	markj
Sponsored by:	The FreeBSD Foundation
Differential revision:	https://reviews.freebsd.org/D27309

sys/kern/kern_exec.c

@@ -1051,6 +1051,8 @@ exec_new_vmspace(struct image_params *imgp, struct sysentvec *sv)
 	sigfastblock_clear(td);
 	umtx_exec(p);
 	itimers_exec(p);
+	if (sv->sv_onexec != NULL)
+		sv->sv_onexec(p, imgp);
 
 	EVENTHANDLER_DIRECT_INVOKE(process_exec, p, imgp);
 

sys/kern/kern_exit.c

@@ -72,6 +72,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/sdt.h>
 #include <sys/shm.h>
 #include <sys/sem.h>
+#include <sys/sysent.h>
 #include <sys/timers.h>
 #include <sys/umtx.h>
 #ifdef KTRACE
@@ -327,6 +328,9 @@ exit1(struct thread *td, int rval, int signo)
 
 	itimers_exit(p);
 
+	if (p->p_sysent->sv_onexit != NULL)
+		p->p_sysent->sv_onexit(p);
+
 	/*
 	 * Check if any loadable modules need anything done at process exit.
 	 * E.g. SYSV IPC stuff.
@@ -561,6 +565,9 @@ exit1(struct thread *td, int rval, int signo)
 	PROC_LOCK(p);
 	p->p_xthread = td;
 
+	if (p->p_sysent->sv_ontdexit != NULL)
+		p->p_sysent->sv_ontdexit(td);
+
 #ifdef KDTRACE_HOOKS
 	/*
 	 * Tell the DTrace fasttrap provider about the exit if it

sys/kern/kern_kthread.c

@@ -39,6 +39,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/resourcevar.h>
 #include <sys/rwlock.h>
 #include <sys/signalvar.h>
+#include <sys/sysent.h>
 #include <sys/sx.h>
 #include <sys/umtx.h>
 #include <sys/unistd.h>
@@ -355,6 +356,10 @@ kthread_exit(void)
 		PROC_UNLOCK(p);
 		kproc_exit(0);
 	}
+
+	if (p->p_sysent->sv_ontdexit != NULL)
+		p->p_sysent->sv_ontdexit(td);
+
 	tidhash_remove(td);
 	umtx_thread_exit(td);
 	tdsigcleanup(td);

sys/kern/kern_thr.c

@@ -353,6 +353,9 @@ kern_thr_exit(struct thread *td)
 		return (0);
 	}
 
+	if (p->p_sysent->sv_ontdexit != NULL)
+		p->p_sysent->sv_ontdexit(td);
+
 	td->td_dbgflags |= TDB_EXIT;
 	if (p->p_ptevents & PTRACE_LWP) {
 		p->p_pendingexits++;

sys/sys/sysent.h

@@ -145,6 +145,9 @@ struct sysentvec {
 	u_long		*sv_hwcap2;	/* Value passed in AT_HWCAP2. */
 	const char	*(*sv_machine_arch)(struct proc *);
 	vm_offset_t	sv_fxrng_gen_base;
+	void		(*sv_onexec)(struct proc *, struct image_params *);
+	void		(*sv_onexit)(struct proc *);
+	void		(*sv_ontdexit)(struct thread *td);
 };
 
 #define	SV_ILP32	0x000100	/* 32-bit executable. */