# Debug

> Debugging is the process of finding and resolving or defects that prevent correct operation of computer software or a system. Debugging tends to be harder when various subsystems are tightly coupled, as changes in one may cause bugs to emerge in another. [Wikipedia](https://en.wikipedia.org/wiki/Debugging)

* [Ubuntu Kernel Debugging Tricks](https://wiki.ubuntu.com/Kernel/KernelDebuggingTricks)

## Kernel Configuration

```bash
    Kernel hacking

        -*- Kernel debugging
        [*]   Magic SysRq key
        -*-   Debug filesystem
        [*]   Detect Soft Lockups
        [ ]   Collect scheduler statistics
        [*]   Debug slab memory allocations
        [*]     Memory leak debugging
        [*]   Mutex debugging, deadlock detection
        [*]   Spinlock debugging
        [*]   Sleep-inside-spinlock checking
        [ ]   kobject debugging
        [ ]   Highmem debugging
        [ ]   Compile the kernel with debug info
```

## Kernel Integration

### Linux Debug Filesystem

> Debugfs exists as a simple way for kernel developers to make information available to user space. Unlike /proc, which is only meant for information about a process, or sysfs, which has strict one-value-per-file rules, debugfs has no rules at all. [Wikipedia](https://en.wikipedia.org/wiki/Debugfs)

* [Linux Kernel Documentation Debugfs](https://www.kernel.org/doc/Documentation/filesystems/debugfs.txt)
* [Linux Kernel Debugfs](https://www.kernel.org/doc/Documentation/filesystems/debugfs.txt)

```bash
    root@edison:~# mount -t debugfs none /sys/kernel/debug
    mount: none is already mounted or /sys/kernel/debug busy
           none is already mounted on /tmp/temptmpfs
    root@edison:~# ls /sys/kernel/debug/
    asoc                  gpio_debug            pmu_sync_d0ix
    bdi                   hid                   pwm
    bluetooth             hsu                   regmap
    boot_params           ieee80211             regulator
    c_states_stat         ignore_add            remoteproc
    cstate_ignore_add     ignore_remove         s3_ctrl
    cstate_ignore_remove  iio                   sched_features
    debug_feature         intel_scu_oshob       soc_thermal
    disable_emmc_ipanic   kprobes               sst
    dma_buf               mce                   suspend_stats
    dri                   mid_pmu_states        tracing
    dump_cmd              mmc0                  usb
    dump_output           mmc1                  wakeup_sources
    dwc3-device.1         mmc2                  watchdog
    dynamic_debug         pmic_ccsm             x86
    emmc_ipanic           pmu_force_d0i0
    gpio                  pmu_force_d0i3
    root@edison:~#
```

### Linux Magic System Request Key Hacks

> It is a 'magical' key combo you can hit which the kernel will respond to regardless of whatever else it is doing, unless it is completely locked up. [Documentation](https://www.kernel.org/doc/Documentation/sysrq.txt)

* [Linux Magic System Request Key Hacks](https://www.kernel.org/doc/Documentation/sysrq.txt)

### Ftrace

* [Debugging the kernel using Ftrace - Part 1](https://lwn.net/Articles/365835/)

```bash
    root@edison:~# cd /sys/kernel/debug/tracing
    root@edison:/sys/kernel/debug/tracing# cat available_tracers 
    blk function_graph wakeup_rt wakeup preemptirqsoff preemptoff irqsoff function nop
    root@edison:/sys/kernel/debug/tracing# echo function > current_tracer
    root@edison:/sys/kernel/debug/tracing# cat current_tracer
    function
```

## Applications / Libraries

### Programs

None


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://theiotlearninginitiative.gitbook.io/embedded-linux/debug.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.