xref: /freebsd/share/man/man4/ksyms.4 (revision ddd5b8e9b4d8957fce018c520657cdfa4ecffad3)
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32.\" $FreeBSD$
33.\"
34.Dd April 5, 2009
35.Dt KSYMS 4
36.Os
37.Sh NAME
38.Nm ksyms
39.Nd kernel symbol table interface
40.Sh SYNOPSIS
41.Cd "device ksyms"
42.Sh DESCRIPTION
43The
44.Pa /dev/ksyms
45character device provides a read-only interface to a snapshot of the kernel
46symbol table.  The in-kernel symbol manager is designed to be able to handle
47many types of symbols tables, however, only
48.Xr elf 5
49symbol tables are supported by this device.  The ELF format image contains two
50sections: a symbol table and a corresponding string table.
51.Bl -tag -width indent -offset indent
52.It Dv Symbol Table
53The SYMTAB section contains the symbol table entries present in the current
54running kernel, including the symbol table entries of any loaded modules. The
55symbols are ordered by the kernel module load time starting with kernel file
56symbols first, followed by the first loaded module's symbols and so on.
57.It Dv String Table
58The STRTAB section contains the symbol name strings from the kernel and any
59loaded modules that the symbol table entries reference.
60.El
61.Pp
62Elf formatted symbol table data read from the
63.Pa /dev/ksyms
64file represents the state of the kernel at the time when the device is opened.
65Since
66.Pa /dev/ksyms
67has no text or data, most of the fields are initialized to NULL.
68The
69.Nm
70driver does not block the loading or unloading of modules into the kernel
71while the
72.Pa /dev/ksyms
73file is open but may contain stale data.
74.Sh IOCTLS
75The
76.Xr ioctl 2
77command codes below are defined in
78.Aq Pa sys/ksyms.h .
79.Pp
80The (third) argument to the
81.Xr ioctl 2
82should be a pointer to the type indicated.
83.Bl -tag -width indent -offset indent
84.It Dv KIOCGSIZE (size_t)
85Returns the total size of the current symbol table.
86This can be used when allocating a buffer to make a copy of
87the kernel symbol table.
88.It Dv KIOCGADDR (void *)
89Returns the address of the kernel symbol table mapped in
90the process memory.
91.El
92.Sh FILES
93.Bl -tag -width /dev/ksymsX
94.It Pa /dev/ksyms
95.El
96.Sh ERRORS
97An
98.Xr open 2
99of
100.Pa /dev/ksyms
101will fail if:
102.Bl -tag -width Er
103.It Bq Er EBUSY
104The device is already open.  A process must close
105.Pa /dev/ksyms
106before it can be opened again.
107.It Bq Er ENOMEM
108There is a resource shortage in the kernel.
109.It Bq Er ENXIO
110The driver was unsuccessful in creating a snapshot of the kernel symbol
111table.  This may occur if the kernel was in the process of loading or
112unloading a module.
113.El
114.Sh SEE ALSO
115.Xr ioctl 2 ,
116.Xr nlist 3 ,
117.Xr elf 5 ,
118.Xr kldload 8
119.Sh HISTORY
120A
121.Nm
122device exists in many different operating systems.
123This implementation is similar in function to the Solaris and NetBSD
124.Nm
125driver.
126.Pp
127The
128.Nm
129driver first appeared in
130.Fx 8.0
131to support
132.Xr lockstat 1 .
133.Sh AUTHORS
134The
135.Nm
136driver was written by
137.An Stacey Son
138.Aq sson@FreeBSD.org .
139.Sh BUGS
140Because files can be dynamically linked into the kernel at any time the symbol
141information can vary.  When you open the
142.Pa /dev/ksyms
143file, you have access to an ELF image which represents a snapshot of the state of the kernel symbol information at that instant in time. Keeping the device open does not block the loading or unloading of kernel modules.  To get a new snapshot you must close and re-open the device.
144.Pp
145A process is only allowed to open the
146.Pa /dev/ksyms
147file once at a time.  The process must close the
148.Pa /dev/ksyms
149before it is allowed to open it again.
150.Pp
151The
152.Nm
153driver uses the calling process' memory address space to store the snapshot.
154.Xr ioctl 2
155can be used to get the memory address where the symbol table is stored to
156save kernel memory.
157.Xr mmap 2
158may also be used but it will map it to another address.
159