linux-kernel-module-cheat/kernel_config_fragment

# Changes to this file are automatically trigger kernel reconfigures
# even without using the linux-reconfigure target.

CONFIG_MODULE_SRCVERSION_ALL=y

# GDB debugging.
CONFIG_DEBUG_FS=y
CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_KERNEL=y
CONFIG_GDB_SCRIPTS=y
# Allow kernel to understand -initrd
CONFIG_BLK_DEV_INITRD=y

# Non-static variables show up on /proc/kallsyms
# https://stackoverflow.com/questions/20196636/does-kallsyms-have-all-the-symbol-of-kernel-functions/44614878#44614878
CONFIG_KALLSYMS_ALL=y

# zcat /proc/config.gz
CONFIG_IKCONFIG=y
CONFIG_IKCONFIG_PROC=y

# TODO make example.
# This seems to allow userspace to create arbitrary configuration trees,
# which kernel modules can then read and interpret.
CONFIG_CONFIGFS_FS=y

# KGDB
CONFIG_CONSOLE_POLL=y
CONFIG_KDB_CONTINUE_CATASTROPHIC=0
CONFIG_KDB_DEFAULT_ENABLE=0x1
CONFIG_KDB_KEYBOARD=y
CONFIG_KGDB=y
CONFIG_KGDB_KDB=y
CONFIG_KGDB_LOW_LEVEL_TRAP=y
CONFIG_KGDB_SERIAL_CONSOLE=y
CONFIG_KGDB_TESTS=y
CONFIG_KGDB_TESTS_ON_BOOT=n
CONFIG_MAGIC_SYSRQ=y
CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x1
CONFIG_SERIAL_KGDB_NMI=n

# Module.symvers in kernel tree and modules tree contains CRC of signatures.
# TODO: I think the CRC are stored in the built kernel and module, and checked
# at insmod, but bgrep did not find it in kernel image.
# Does not show in /proc/kallyms either.
CONFIG_MODVERSIONS=y

# ftrace
CONFIG_DYNAMIC_FTRACE=y
CONFIG_FTRACE=y
CONFIG_FTRACE_SYSCALLS=y
CONFIG_FUNCTION_GRAPH_TRACER=y
CONFIG_FUNCTION_PROFILER=y
CONFIG_FUNCTION_TRACER=y
CONFIG_HWLAT_TRACER=y
CONFIG_IRQSOFF_TRACER=y
CONFIG_SCHED_TRACER=y
CONFIG_STACK_TRACER=y
CONFIG_TRACER_SNAPSHOT=y

## Networking

# Will everything blow up?
# https://superuser.com/questions/684005/how-does-one-permanently-disable-gnu-linux-networking/1255015#1255015
#CONFIG_NET=n

# If given, we can use QEMU 2.9.0 default x86 networking without any -net or -netdev options,
# since E1000 is the default networking device as mentioned at:
# https://en.wikibooks.org/w/index.php?title=QEMU/Networking&oldid=3268753
CONFIG_E1000=y

## x86

# https://stackoverflow.com/questions/20069620/print-kernels-page-table-entries
# cat /sys/kernel/debug/kernel_page_tables
CONFIG_X86_PTDUMP=y

## ARM

# LEDs:
#
#     cd /sys/class/leds/versatile:0
#     cat max_brightness
#     echo 255 >brightness
#
# https://raspberrypi.stackexchange.com/questions/697/how-do-i-control-the-system-leds-using-my-software
#
# Relevant QEMU files:
#
# - hw/arm/versatilepb.c
# - hw/misc/arm_sysctl.c
#
# Relevant kernel files:
#
# - arch/arm/boot/dts/versatile-pb.dts
# - drivers/leds/led-class.c
# - drivers/leds/leds-sysctl.c
#
# Try hacking QEMU's `hw/misc/arm_sysctl.c` with a printf:
#
#     static void arm_sysctl_write(void *opaque, hwaddr offset,
#                                 uint64_t val, unsigned size)
#     {
#         arm_sysctl_state *s = (arm_sysctl_state *)opaque;
#
#         switch (offset) {
#         case 0x08: /* LED */
#             printf("LED val = %llx\n", (unsigned long long)val);
#
# to obeserve when the callback is made. But beware that one of the LEDs
# has a heartbeat trigger by default (specified on dts), so it will produce a lot of output.
CONFIG_LEDS_CLASS=y
CONFIG_LEDS_CLASS_FLASH=y
CONFIG_LEDS_SYSCON=y
CONFIG_LEDS_TRIGGERS=y
CONFIG_LEDS_TRIGGER_BACKLIGHT=y
CONFIG_LEDS_TRIGGER_CPU=y
CONFIG_LEDS_TRIGGER_DEFAULT_ON=y
CONFIG_LEDS_TRIGGER_GPIO=y
CONFIG_LEDS_TRIGGER_HEARTBEAT=y
CONFIG_LEDS_TRIGGER_ONESHOT=y
CONFIG_LEDS_TRIGGER_TIMER=y
CONFIG_NEW_LEDS=y

# GPIO.
CONFIG_ARM_AMBA=y
CONFIG_GPIOLIB=y
CONFIG_GPIO_SYSFS=y
CONFIG_GPIO_PL061=y

# In target:
#
#     modprobe dummy-irq irq=34
#     insmod /platform_device.ko
#
# Outcome:
#
#     lkmc_platform_device_write offset=0 value=12345678 size=4
#     dummy-irq: interrupt occurred on IRQ 34
#
# When the device generates an IRQ, the dummy module also snoops it.
#
# The IRQ number 34 was found by via dmesg on a previous "insmod /platform_device.ko".
CONFIG_DUMMY_IRQ=m

## aarch64

# For some reason not selected by default as it was for arm, and pci modules fail to build.
# Not that we have PCI working on ARM anyways.
CONFIG_PCI=y

# Like CONFIG_X86_PTDUMP for ARM.
CONFIG_ARM64_PTDUMP=y

## UIO

# Userspace drivers: allow you to handle IRQs and do memory IO from userland through a /dev file.
#
# Superseded by the more featureful VFIO.
#
# Documentation/DocBook/uio-howto.tmpl contains actual userland examples
# for the generic examples under drivers/uio
#
# UIO interface in a nutshell:
#
# - blocking read / poll: waits until interrupts
# - write: call irqcontrol callback. Default: 0 or 1 to enable / disable interrupts.
# - mmap: access device memory

# All other UIO depend on this module.
CONFIG_UIO=m

# Generic platform devices.
# https://yurovsky.github.io/2014/10/10/linux-uio-gpio-interrupt/
CONFIG_UIO_DMEM_GENIRQ=m
CONFIG_UIO_PDRV_GENIRQ=m

# https://github.com/rumpkernel/wiki/wiki/Howto:-Accessing-PCI-devices-from-userspace
# /sys/class/uio/
# /sys/class/uio/uio0
CONFIG_UIO_PCI_GENERIC=m