profil(2)

NAME

profil - control process profiling

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <unistd.h>
int
profil(char *samples, size_t size, vm_offset_t  offset,  int
scale);

DESCRIPTION

The 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

samples
buffer. The frequency of the profiling clock is recorded in

the header
in the profiling output file.

The buffer samples contains size bytes and is divided into a

series of
16-bit bins. Each bin counts the number of times the pro

gram counter was
in a particular address range in the process when a profil

ing clock tick
occurred while profiling was enabled. For a given program

counter
address, the number of the corresponding bin is given by the

relation:

[(pc - offset) / 2] * scale / 65536

The offset argument is the lowest address at which the ker

nel takes program counter samples. The 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 scale value of 0 disables profiling.

RETURN VALUES

The profil() function returns the value 0 if successful;

otherwise the
value -1 is returned and the global variable errno is set to

indicate the
error.

FILES

/usr/lib/gcrt0.o profiling C run-time startup file
gmon.out conventional name for profiling output

file

ERRORS

The following error may be reported:

[EFAULT] The buffer samples contains an invalid

address.

SEE ALSO

gprof(1)

HISTORY

The profil() function appeared in Version 7 AT&T UNIX.

BUGS

This routine should be named profile().

The samples argument should really be a vector of type

unsigned short.

The format of the gmon.out file is undocumented.

BSD June 4, 1993

BSD