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libc: mark exits as profile-able

Exits had been marked as noprof, this was likely done because
there would be some noise added by _profdump itself (added as an onexit handler).
However, knowing if your atexit handlers are taking up a lot of time is useful,
and its possible to all but remove the impact by stopping the clock before we call things
like create and print.

--- a/sys/src/libc/port/exits.c

+++ b/sys/src/libc/port/exits.c

@@ -3,8 +3,6 @@

 void (*_onexit)(void);

-#pragma profile off

-

 _Noreturn void

 exits(char *s)

 {

--- a/sys/src/libc/port/profile.c

+++ b/sys/src/libc/port/profile.c

@@ -123,6 +123,7 @@

 	Plink *p;

 	char *vp;

 	char filename[64];

+	long pid;

 	uchar hdr[3+1+8] = {'p', 'r', 0x0f, 0x2};

 	if (_tos->prof.what == 0)

@@ -129,19 +130,11 @@

 		return;	/* No profiling */

 	if (_tos->prof.pid != 0 && _tos->pid != _tos->prof.pid)

 		return;	/* Not our process */

-	if(perr)

-		fprint(2, "%lud Prof errors\n", perr);

+	/* make sure data gets dumped once */

 	_tos->prof.pp = nil;

-	if (_tos->prof.pid)

-		snprint(filename, sizeof filename - 1, "prof.%ld", _tos->prof.pid);

-	else

-		snprint(filename, sizeof filename - 1, "prof.out");

-	f = create(filename, OWRITE|OCEXEC, 0666);

-	if(f < 0) {

-		perror("create prof.out");

-		return;

-	}

-	_tos->prof.pid = ~0;	/* make sure data gets dumped once */

+	pid = _tos->prof.pid;

+	_tos->prof.pid = ~0;

+	

 	switch(_tos->prof.what){

 	case Profkernel:

 		cycles((uvlong*)&_tos->prof.first->time);

@@ -158,6 +151,19 @@

 		_tos->prof.first->time = _tos->clock;

 		break;

 	}

+

+	if(perr)

+		fprint(2, "%lud Prof errors\n", perr);

+	if (pid)

+		snprint(filename, sizeof filename - 1, "prof.%ld", pid);

+	else

+		snprint(filename, sizeof filename - 1, "prof.out");

+	f = create(filename, OWRITE|OCEXEC, 0666);

+	if(f < 0) {

+		perror("create prof.out");

+		return;

+	}

+

 	hdr[4+0] = _tos->cyclefreq>>56;

 	hdr[4+1] = _tos->cyclefreq>>48;

 	hdr[4+2] = _tos->cyclefreq>>40;

-- 

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