ksyms —
kernel
symbol table interface
device ksyms
The
/dev/ksyms character device provides a
read-only interface to a snapshot of the kernel symbol table. The in-kernel
symbol manager is designed to be able to handle many types of symbols tables,
however, only
elf(5) symbol tables are supported
by this device. The ELF format image contains two sections: a symbol table and
a corresponding string table.
Symbol
Table- The SYMTAB section contains the symbol table entries
present in the current running kernel, including the symbol table entries
of any loaded modules. The symbols are ordered by the kernel module load
time starting with kernel file symbols first, followed by the first loaded
module's symbols and so on.
String
Table- The STRTAB section contains the symbol name strings from
the kernel and any loaded modules that the symbol table entries
reference.
Elf formatted symbol table data read from the
/dev/ksyms file represents the state of the
kernel at the time when the device is opened. Since
/dev/ksyms has no text or data, most of the
fields are initialized to NULL. The
ksyms driver
does not block the loading or unloading of modules into the kernel while the
/dev/ksyms file is open but may contain stale
data.
- /dev/ksyms
-
An
open(2) of
/dev/ksyms will fail if:
- [
EBUSY]
- The device is already open. A process must close
/dev/ksyms before it can be opened
again.
- [
ENOMEM]
- There is a resource shortage in the kernel.
- [
ENXIO]
- The driver was unsuccessful in creating a snapshot of the
kernel symbol table. This may occur if the kernel was in the process of
loading or unloading a module.
nlist(3),
elf(5),
kldload(8)
A
ksyms device exists in many different operating
systems. This implementation is similar in function to the Solaris and NetBSD
ksyms driver.
The
ksyms driver first appeared in
FreeBSD 8.0 to support
lockstat(1).
The
ksyms driver was written by
Stacey Son
<
[email protected]>.
Because files can be dynamically linked into the kernel at any time the symbol
information can vary. When you open the
/dev/ksyms file, 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.
A process is only allowed to open the
/dev/ksyms
file once at a time. The process must close the
/dev/ksyms before it is allowed to open it
again.