---
name: "kallsyms"
section: "8"
platform: "linux"
package: "modutils"
version: "2.4.27.0-6"
release: "Debian 4.0 (Etch)"
platforms: ["linux"]
url: "https://new.carta.tech/kallsyms"
---

# kallsyms(8)

Extract all kernel symbols for debugging

## NAME

kallsyms - Extract all kernel symbols for debugging

## SYNOPSIS

**kallsyms** \[-Vh\] kernel\_filename

## DESCRIPTION

**Kallsyms** extracts all the non-stack symbols from a kernel and builds a data blob that can be linked into that kernel for use by debuggers.

A normal kernel only exports symbols that are used by modules. For debugging you may want a list of all the non-stack symbols, not just the exported ones. **kallsyms** extracts all sections and symbols from a kernel, constructs a list of the sections, symbols and their addresses and writes a relocatable object containing just the \_\_kallsyms section. After the \_\_kallsyms section is linked into the kernel and the kernel has been booted, any debugger can use the data in the \_\_kallsyms section to get better symbol resolution.

For example, a debugger can use the \_\_kallsyms data to resolve a kernel address to:

- \*

  The owning kernel or module.

- \*

  The section within the owning code.

- \*

  The nearest symbol.

## OPTIONS

- **-h**, **--help**

  Display a summary of options and exit.

- **-V**, **--version**

  Display the version of **kallsyms** and exit.

## LINKER PASSES

To create a kernel containing an accurate \_\_kallsyms section, you have to make four linker passes instead of the normal single link step. kallsyms and the linker are fast, the three extra steps take a few seconds on a P200.

- 1

  The initial build of the kernel, without any \_\_kallsyms data. Run **kallsyms** against the output of this link, creating a relocatable object which contains all the sections and symbols in the raw kernel.

- 2

  Link the kernel again, this time including the **kallsyms** output from step (1). Adding the \_\_kallsyms section changes the number of sections and many of the kernel symbol offsets so run **kallsyms** again against the second link, again saving the relocatable output.

- 3

  Link the kernel again, this time including the **kallsyms** output from step (2). Run **kallsyms** against the latest version of the kernel. The size and position of the \_\_kallsyms section on this run is now stable, none of the kernel sections or symbols will change after this run. The **kallsyms** output contains the final values of the kernel symbols.

- 4

  Link the final kernel, including the **kallsyms** output from step (3).

## DATA FORMAT

The \_\_kallsyms section is a bit unusual. It deliberately has no relocatable data, all "pointers" are represented as byte offsets into the section or as absolute numbers. This means it can be stored anywhere without relocation problems. In particular it can be stored within a kernel image, it can be stored separately from the kernel image, it can be appended to a module just before loading, it can be stored in a separate area, etc.

*/usr/include/sys/kallsyms.h* contains the mappings for the \_\_kallsyms data.

### Header

- \*

  Size of header.

- \*

  Total size of the \_\_kallsyms data, including strings.

- \*

  Number of sections. This only included sections which are loaded into memory.

- \*

  Offset to the first section entry from start of the \_\_kallsyms header.

- \*

  Size of each section entry, excluding the name string.

- \*

  Number of symbols.

- \*

  Offset to the first symbol entry from the start of the \_\_kallsyms header.

- \*

  Size of each symbol entry, excluding the name string.

- \*

  Offset to the first string from the start of the \_\_kallsyms header.

- \*

  Start address of the first section\[1\].

- \*

  End address of the last section\[1\].

### Section entry

One entry per loaded section. Since \_\_kallsyms is a loaded section, if the input file contains a \_\_kallsyms section then it is included in this list.

- \*

  Start of the section within the kernel\[1\].

- \*

  Size of section.

- \*

  Offset to the name of section, from the start of the \_\_kallsyms strings.

- \*

  Section flags, from the original Elf section.

### Symbol entry

One per symbol in the input file. Only symbols that fall within loaded sections are stored.

- \*

  Offset to the \_\_kallsyms section entry that this symbol falls within. The offset is from the start of the \_\_kallsyms section entries.

- \*

  Address of the symbol within the kernel\[1\]. The symbols are sorted in ascending order on this field.

- \*

  Offset to the name of symbol, from the start of the \_\_kallsyms strings.

### Strings

A set of NUL terminated strings. Each name is referenced using an offset from the start of the \_\_kallsyms string area.

### Note \[1\]

These fields are exceptions to the "everything is an offset" rule. They contain absolute addresses within the kernel.

## SEE ALSO

[**insmod**(8)](/insmod/8.md).

## HISTORY

Initial version by Keith Owens \<kaos@ocs.com.au\>, April 2000