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 6 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.

Debian                                          December 1, 2017                                       PROFIL(2)