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ksyms(4d)
Device Drivers & /dev files ksyms(4D)
NAME
ksyms - kernel symbols
SYNOPSIS
/dev/ksyms
DESCRIPTION
The file /dev/ksyms is a character special file that allows read-only
access to an ELF format image containing two sections: a symbol table
and a corresponding string table. The contents of the symbol table
reflect the symbol state of the currently running kernel. You can
determine the size of the image with the fstat() system call. The rec‐
ommended method for accessing the /dev/ksyms file is by using the ELF
access library. See elf(3ELF) for details. If you are not familiar with
ELF format, see a.out(5).
/dev/ksyms is an executable for the processor on which you are access‐
ing it. It contains ELF program headers which describe the text and
data segment(s) in kernel memory. Since /dev/ksyms has no text or data,
the fields specific to file attributes are initialized to NULL. The
remaining fields describe the text or data segment(s) in kernel memory.
Symbol table The SYMTAB section contains the symbol table entries
present in the currently running kernel. This section
is ordered as defined by the ELF definition with
locally-defined symbols first, followed by globally-
defined symbols. Within symbol type, the symbols are
ordered by kernel module load time. For example, the
kernel file symbols are first, followed by the first
module's symbols, and so on, ending with the symbols
from the last module loaded.
The section header index (st_shndx) field of each sym‐
bol entry in the symbol table is set to SHN_ABS,
because any necessary symbol relocations are performed
by the kernel link editor at module load time.
String table The STRTAB section contains the symbol name strings
that the symbol table entries reference.
SEE ALSO
elf(3ELF), stat(2), kvm_open(3KVM), mem(4D), a.out(5), kernel(8)
WARNINGS
The kernel is dynamically configured. It loads kernel modules when nec‐
essary. Because of this aspect of the system, the symbol information
present in the running system can vary from time to time, as kernel
modules are loaded and unloaded.
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 informa‐
tion at that instant in time. While the /dev/ksyms file remains open,
kernel module autounloading is disabled, so that you are protected from
the possibility of acquiring stale symbol data. Note that new modules
can still be loaded, however. If kernel modules are loaded while you
have the /dev/ksyms file open, the snapshot held by you will not be
updated. In order to have access to the symbol information of the newly
loaded modules, you must first close and then reopen the /dev/ksyms
file. Be aware that the size of the /dev/ksyms file will have changed.
You will need to use the fstat() function (see stat(2)) to determine
the new size of the file.
Avoid keeping the /dev/ksyms file open for extended periods of time,
either by using kvm_open(3KVM) of the default namelist file or with a
direct open. There are two reasons why you should not hold /dev/ksyms
open. First, the system's ability to dynamically configure itself is
partially disabled by the locking down of loaded modules. Second, the
snapshot of symbol information held by you will not reflect the symbol
information of modules loaded after your initial open of /dev/ksyms.
Note that the ksyms driver is a loadable module, and that the kernel
driver modules are only loaded during an open system call. Thus it is
possible to run stat(2) on the /dev/ksyms file without causing the
ksyms driver to be loaded. In this case, the file size returned is
UNKNOWN_SIZE. A solution for this behavior is to first open the
/dev/ksyms file, causing the ksyms driver to be loaded (if necessary).
You can then use the file descriptor from this open in a fstat() system
call to get the file's size.
NOTES
The kernel virtual memory access library (libkvm) routines use
/dev/ksyms as the default namelist file. See kvm_open(3KVM) for
details.
Oracle Solaris 11.4 11 Dec 2000 ksyms(4D)