PROFIL(2)                 OpenBSD Programmer's Manual                PROFIL(2)

NAME
     profil - control process profiling



SYNOPSIS
     #include <unistd.h>

     int
     profil(char *samples, size_t size, u_long offset, u_int scale);

DESCRIPTION
     The profil() function enables or disables program counter profiling of
     the current process.  If profiling is enabled, then at every clock tick,
     the kernel updates an appropriate count in the samples buffer.

     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 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 pro-
     gram 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)

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.

OpenBSD 2.6                      June 4, 1993                                1