LIBRARY

Lb libc

SYNOPSIS

In unistd.h Ft int Fn profil char *samples size_t size vm_offset_t offset int scale

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.

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:

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

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.

RETURN VALUES

Rv -std profil

FILES

/usr/lib/gcrt0.o

profiling C run-time startup file

gmon.out

conventional name for profiling output file

HISTORY

The Fn profil function appeared in AT&T System v7 .