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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 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.