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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.

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.