.\"	$OpenBSD: profil.2,v 1.9 2007/05/31 19:19:33 jmc Exp $
.\"	$NetBSD: profil.2,v 1.3 1995/11/22 23:07:23 cgd Exp $
.\"
.\" Copyright (c) 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Donn Seeley of BSDI.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\"
.\"	@(#)profil.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: May 31 2007 $
.Dt PROFIL 2
.Os
.Sh NAME
.Nm profil
.Nd control process profiling
.Sh SYNOPSIS
.Fd #include <unistd.h>
.Ft int
.Fn profil "char *samples" "size_t size" "u_long offset" "u_int scale"
.Sh DESCRIPTION
The
.Fn profil
function enables or disables program counter profiling of the current process.
If profiling is enabled, then at every clock tick,
the kernel updates an appropriate count in the
.Fa samples
buffer.
.Pp
The buffer
.Fa samples
contains
.Fa size
bytes and is divided into a series of 16-bit bins.
Each bin counts the number of times the program counter was in a particular
address range in the process when a clock tick occurred while profiling
was enabled.
For a given program counter address, the number of the corresponding bin
is given by the relation:
.Bd -literal -offset indent
[(pc - offset) / 2] * scale / 65536
.Ed
.Pp
The
.Fa offset
parameter is the lowest address at which the kernel takes program
counter samples.
The
.Fa scale
parameter ranges from 1 to 65536 and can be used to change the
span of the bins.
A scale of 65536 maps each bin to 2 bytes of address range;
a scale of 32768 gives 4 bytes, 16384 gives 8 bytes and so on.
Intermediate values provide approximate intermediate ranges.
A
.Fa scale
value of 0 disables profiling.
.Sh RETURN VALUES
If the
.Fa scale
value is nonzero and the buffer
.Fa samples
contains an illegal address,
.Fn profil
returns \-1, profiling is terminated, and
.Va errno
is set appropriately.
Otherwise,
.Fn profil
returns 0.
.Sh FILES
.Bl -tag -width /usr/lib/gcrt0.o -compact
.It Pa /usr/lib/gcrt0.o
profiling C run-time startup file
.It Pa gmon.out
conventional name for profiling output file
.El
.Sh ERRORS
The following error may be reported:
.Bl -tag -width Er
.It Bq Er EFAULT
The buffer
.Fa samples
contains an invalid address.
.El
.Sh SEE ALSO
.Xr gprof 1
.\" .Sh HISTORY
.\" wish I knew...  probably v7.
.Sh BUGS
This routine should be named
.Fn profile .
.Pp
The
.Fa samples
argument should really be a vector of type
.Fa "unsigned short" .
.Pp
The format of the gmon.out file is undocumented.