PROFIL(2) BSD System Calls Manual PROFIL(2)NAME
profil -- control process profiling
LIBRARY
Standard C Library (libc, -lc)
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 program 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. This may be different if the PROFDIR environment variable is set.
ERRORS
The following error may be reported:
[EFAULT] The buffer samples contains an invalid address.
SEE ALSO gprof(1), moncontrol(3)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.
BSD June 4, 1993 BSD
Check Out this Related Man Page
profil(2) System Calls Manual profil(2)NAME
profil - Starts and stops execution profiling
SYNOPSIS
void profil( unsigned short *short_buffer, unsigned int buffer_size, void *offset, unsigned int scale ); #include
<sys/resource.h>
void profil(
struct profil_args *args,
int buffer_size,
-1,
unsigned long flags);
PARAMETERS
Points to an area of memory in the user address space. Its length (in bytes) is given by the buffer_size parameter. Specifies the length
(in bytes) of the buffer. When offset is -1, indicating that the extended profil format shown in the second synopsis above is in use, the
buffer_size parameter indicates the number of profil_args structures in the args array. Specifies the delta of program counter start and
buffer; for example, an offset of 0 (zero) implies that text begins at 0. When offset is -1, the profil call is interpreted as a call to
profile multiple discontiguous address ranges, such as those in an executable and its shared libraries. In this type of profil call, which
has the format shown in the second synopsis above, the buffer_size parameter indicates the number of profil_args structures in the args
array. Specifies the mapping factor between the program counter and short_buffer. When offset is -1, specifies an array of up to 64
struct profil_args structures, each describing a single address range in which profiling is to occur. Specifies flags that modify the
behavior of a profil call that profiles multiple discontiguous address ranges. This argument is reserved for future use and should be 0.
DESCRIPTION
The profil() function controls execution profiling.
The short_buffer parameter points to an area of memory whose length (in bytes) is given by the buffer_size parameter. After this call, the
process' program counter is examined at regular intervals (for example, at 1024 Hz). To determine the interval for your system, use the
getsysinfo(2) system call with GSI_CLK_TCK as the operation parameter.
The value of the offset parameter is subtracted from the program counter, and the result multiplied by the scale parameter. The corre-
sponding location in the short_buffer parameter is incremented if the resulting number is less than the buffer_size parameter.
The scale parameter is interpreted as an unsigned, fixed point fraction with 16 bits of mantissa: 0x10000 means that the address range
has the same number of bytes as the short_buffer (that is, two bytes of instruction map into each short_buffer element); 0x8000 maps four
bytes of instructions into each short_buffer element; and so on. The special scale factor of 2 maps all instructions onto the beginning of
the short_buffer (producing a non-interrupting clock).
Profiling is turned off by giving a scale parameter of either zero (0) or 1. Profiling is turned off when an execve() is executed. Pro-
filing remains on in both the parent and child processes after a fork. Profiling is turned off if an update in the short_buffer parameter
would cause a memory fault.
If the process contains multiple threads, each will be independently sampled and the counts will reflect the sum of the samples for all of
the threads.
The second form of profil call allows you to profile multiple disjoint address ranges, such as an executable and its shared libraries.
This form of profil call must specify an offset of -1. Its first argument, args, specifies an array of struct profil_args structures, each
describing a single address range in which profiling is to occur. The buffer_size argument indicates the number of profil_args structures
in the args array.
The members of each profil_args structure in the array pointed to by args are similar to the arguments in the traditional profil call,
except that the buffer field is an array of unsigned ints instead of an array of unsigned shorts, and the highpc and lowpc members specify
both ends of the address range to be profiled. The scale is still the ratio of bytes in the address range to bytes in the buffer.
The following are the contents of a profil_args struct:
struct profil_args {
unsigned int *buffer;
void *highpc;
void *lowpc
void *offset;
unsigned int scale;
}
All the address ranges specified in the array must be non-overlapping, and be ordered by decreasing lowpc value (that is, addresses ranges
appear in the array in decreasing beginning address order). As with a traditional profil call, profiling is turned off (for a given
address range) if an update in the buffer (specified by the struct profil_args for that address range) would cause a memory fault.
You can stop profiling started by either type of profil call by issuing the following command: profil(0,0,0,0)
Because a traditional profil call stops all profiling started with an extended call, and an extended profil call stops all profiling
started with a traditional call, a thread never needs to record both kinds of profiling activity at the same time. That is, profiling a
single address range with a buffer of short counters and profiling multiple address ranges in buffers with int counters are mutually
exclusive in a given thread. Although a thread can be switched from one type of profiling to the other with any call to the other inter-
face and different profiling mechanisms can operate on separate threads simultaneously, use of a single profiling interface is recommended
in a single application.
RELATED INFORMATION
Functions: exec(2), fork(2), getsysinfo(2), monitor(3)
Commands: prof(1) delim off
profil(2)