xref: /freebsd/lib/libsys/profil.2 (revision 3fb8f1272b50cb87cb624b321f7b81e76627c437)
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31.Dd December 1, 2017
32.Dt PROFIL 2
33.Os
34.Sh NAME
35.Nm profil
36.Nd control process profiling
37.Sh LIBRARY
38.Lb libc
39.Sh SYNOPSIS
40.In unistd.h
41.Ft int
42.Fn profil "char *samples" "size_t size" "vm_offset_t offset" "int scale"
43.Sh DESCRIPTION
44The
45.Fn profil
46system call enables or disables
47program counter profiling of the current process.
48If profiling is enabled,
49then at every profiling clock tick,
50the kernel updates an appropriate count in the
51.Fa samples
52buffer.
53The frequency of the profiling clock is recorded
54in the header in the profiling output file.
55.Pp
56The buffer
57.Fa samples
58contains
59.Fa size
60bytes and is divided into
61a series of 16-bit bins.
62Each bin counts the number of times the program counter
63was in a particular address range in the process
64when a profiling clock tick occurred while profiling was enabled.
65For a given program counter address,
66the number of the corresponding bin is given
67by the relation:
68.Bd -literal -offset indent
69[(pc - offset) / 2] * scale / 65536
70.Ed
71.Pp
72The
73.Fa offset
74argument is the lowest address at which
75the kernel takes program counter samples.
76The
77.Fa scale
78argument ranges from 1 to 65536 and
79can be used to change the span of the bins.
80A scale of 65536 maps each bin to 2 bytes of address range;
81a scale of 32768 gives 4 bytes, 16384 gives 8 bytes and so on.
82Intermediate values provide approximate intermediate ranges.
83A
84.Fa scale
85value of 0 disables profiling.
86.Sh RETURN VALUES
87.Rv -std profil
88.Sh FILES
89.Bl -tag -width /usr/lib/gcrt0.o -compact
90.It Pa /usr/lib/gcrt0.o
91profiling C run-time startup file
92.It Pa gmon.out
93conventional name for profiling output file
94.El
95.Sh ERRORS
96The following error may be reported:
97.Bl -tag -width Er
98.It Bq Er EFAULT
99The buffer
100.Fa samples
101contains an invalid address.
102.El
103.Sh SEE ALSO
104.Xr gprof 1
105.Sh HISTORY
106The
107.Fn profil
108functionality first appeared in
109.At v3 .
110.Sh BUGS
111This routine should be named
112.Fn profile .
113.Pp
114The
115.Fa samples
116argument should really be a vector of type
117.Fa "unsigned short" .
118.Pp
119The format of the gmon.out file is undocumented.
120