Configuration Options for Debugging Linux Kernel

Linux supports various configuration options for debugging Linux Kernel. Some of these options are not supported on all the platforms. Some of the available configuration options are

• CONFIG_DEBUG_KERNEL
  This option just makes other debugging options available; it should be turned on but does not, by itself, enable any features.
• CONFIG_DEBUG_SLAB
  This crucial option turns on several types of checks in the kernel memory allocation functions; with these checks enabled, it is possible to detect a number of memory overrun and missing initialization errors. Each byte of allocated memory is set to 0xa5 before being handed to the caller and then set to 0x6b when it is freed. If you ever see either of those “poison” patterns repeating in output from your driver (or often in an oops listing), you’ll know exactly what sort of error to look for. When debugging is enabled, the kernel also places special guard values before and after every allocated memory object; if those values ever get changed, the kernel knows that somebody has overrun a memory allocation, and it complains loudly. Various checks for more obscure errors are enabled as well.
• CONFIG_DEBUG_PAGEALLOC
  Full pages are removed from the kernel address space when freed. This option can slow things down significantly, but it can also quickly point out certain kinds of memory corruption errors.
• CONFIG_DEBUG_SPINLOCK
  With this option enabled, the kernel catches operations on uninitialized spinlocks and various other errors (such as unlocking a lock twice).
• CONFIG_DEBUG_SPINLOCK_SLEEP
  This option enables a check for attempts to sleep while holding a spinlock. In fact, it complains if you call a function that could potentially sleep, even if the call in question would not sleep.
• CONFIG_INIT_DEBUG Items marked with _ _init (or _ _initdata) are discarded after system initialization or module load time. This option enables checks for code that attempts to access initialization-time memory after initialization is complete.
• CONFIG_DEBUG_INFO
  This option causes the kernel to be built with full debugging information included. You’ll need that information if you want to debug the kernel with gdb. You may also want to enable CONFIG_FRAME_POINTER if you plan to use gdb.
• CONFIG_MAGIC_SYSRQ Enables the “magic SysRq” key.
• CONFIG_DEBUG_STACKOVERFLOW and CONFIG_DEBUG_STACK_USAGE
  These options can help track down kernel stack overflows. A sure sign of a stack overflow is an oops listing without any sort of reasonable back trace. The first option adds explicit overflow checks to the kernel; the second causes the kernel to monitor stack usage and make some statistics available via the magic SysRq key.
• CONFIG_KALLSYMS
  This option causes kernel symbol information to be built into the kernel; it is enabled by default. The symbol information is used in debugging contexts; without it, an oops listing can give you a kernel traceback only in hexadecimal, which is not very useful.
• CONFIG_IKCONFIG and CONFIG_IKCONFIG_PROC
  These options cause the full kernel configuration state to be built into the kernel and to be made available via /proc. Most kernel developers know which configuration they used and do not need these options (which make the kernel bigger). They can be useful, though, if you are trying to debug a problem in a kernel built by somebody else.
• CONFIG_ACPI_DEBUG
  This option turns on verbose ACPI (Advanced Configuration and Power Interface) debugging information, which can be useful if you suspect a problem related to ACPI.
• CONFIG_DEBUG_DRIVER
  Turns on debugging information in the driver core, which can be useful for tracking down problems in the low-level support code.
• CONFIG_INPUT_EVBUG
  This option turns on verbose logging of input events. If you are working on a driver for an input device, this option may be helpful. Be aware of the security implications of this option, however: it logs everything you type, including your passwords.
• CONFIG_PROFILING
  Profiling is normally used for system performance tuning, but it can also be useful for tracking down some kernel hangs and related problems.

Example

Kernel has infrastructure for detecting all sorts of atomicity violations. Below configuration will help debug potential bugs including calling schedule() while holding a lock, issuing a blocking memory allocation while holding a lock, or sleeping while holding a reference to per-CPU data.

CONFIG_PREEMPT=y
CONFIG_DEBUG_KERNEL=y
CONFIG_KALLSYMS=y
CONFIG_SPINLOCK_SLEEP=y