PROFIL(2)

NAME
profil - control process profiling

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

DESCRIPTION
The profil() function 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 parameter is the lowest address at which the kernel takes program counter samples. The 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 scale value of 0 disables profiling.

RETURN VALUES
If the scale value is nonzero and the buffer samples contains an illegal address, profil() returns -1, profiling is terminated and errno is set appropriately. Otherwise profil() returns 0.

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
A profil() function call appeared in 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.