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.\"	@(#)profil.2	8.1 (Berkeley) 6/4/93
.\"
.Dd December 1, 2017
.Dt PROFIL 2
.Os
.Sh NAME
.Nm profil
.Nd control process profiling
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn profil "char *samples" "size_t size" "vm_offset_t offset" "int scale"
.Sh DESCRIPTION
The
.Fn profil
system call enables or disables
program counter profiling of the current process.
If profiling is enabled,
then at every profiling clock tick,
the kernel updates an appropriate count in the
.Fa samples
buffer.
The frequency of the profiling clock is recorded
in the header in the profiling output file.
.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 profiling 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
argument is the lowest address at which
the kernel takes program counter samples.
The
.Fa scale
argument 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
.Rv -std profil
.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
The
.Fn profil
function appeared in
.At v6 .
.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.