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 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:

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

The offset argument is the lowest address at which the kernel 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.

HISTORY

The profil() functionality first appeared in Version 3 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.