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     profil — control process profiling


     Standard C Library (libc, -lc)


     #include <unistd.h>

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


     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.


     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.


     /usr/lib/gcrt0.o  profiling C run-time startup file
     gmon.out          conventional name for profiling output file


     The following error may be reported:

     [EFAULT]           The buffer samples contains an invalid address.




     The profil() function appeared in Version 7 AT&T UNIX.


     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.