mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
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readme: move leds and gpio into hardware models section
This commit is contained in:
Ciro Santilli
204
README.adoc
204
README.adoc
@@ -3555,108 +3555,6 @@ Looks like a recompile is needed to modify the image...
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* https://superuser.com/questions/736423/changing-kernel-bootsplash-image
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* https://unix.stackexchange.com/questions/153975/how-to-change-boot-logo-in-linux-mint
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=== GPIO
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TODO: broken. Was working before we moved `arm` from `-M versatilepb` to `-M virt` around af210a76711b7fa4554dcc2abd0ddacfc810dfd4. Either make it work on `-M virt` if that is possible, or document precisely how to make it work with `versatilepb`, or hopefully `vexpress` which is newer.
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QEMU does not have a very nice mechanism to observe GPIO activity: https://raspberrypi.stackexchange.com/questions/56373/is-it-possible-to-get-the-state-of-the-leds-and-gpios-in-a-qemu-emulation-like-t/69267#69267
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The best you can do is to hack our link:build[] script to add:
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....
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HOST_QEMU_OPTS='--extra-cflags=-DDEBUG_PL061=1'
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....
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where link:http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0190b/index.html[PL061] is the dominating ARM Holdings hardware that handles GPIO.
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Then compile with:
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....
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./build -aa -b br2_gpio -c kernel_config_fragment/gpio -l
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....
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then test it out with:
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....
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/gpio.sh
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....
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Buildroot's Linux tools package provides some GPIO CLI tools: `lsgpio`, `gpio-event-mon`, `gpio-hammer`, TODO document them here.
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Those broke MIPS build in 2017-02: https://bugs.busybox.net/show_bug.cgi?id=10276 and so we force disable them in our MIPS build currently.
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=== LEDs
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TODO: broken when `arm` moved to `-M virt`, same as <<gpio>>.
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Try hacking QEMU's `hw/misc/arm_sysctl.c` with a printf:
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....
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static void arm_sysctl_write(void *opaque, hwaddr offset,
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uint64_t val, unsigned size)
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{
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arm_sysctl_state *s = (arm_sysctl_state *)opaque;
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switch (offset) {
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case 0x08: /* LED */
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printf("LED val = %llx\n", (unsigned long long)val);
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....
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and then rebuild with:
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....
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./build -aa -c kernel_config_fragment/leds -lq
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....
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But beware that one of the LEDs has a heartbeat trigger by default (specified on dts), so it will produce a lot of output.
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And then activate it with:
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....
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cd /sys/class/leds/versatile:0
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cat max_brightness
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echo 255 >brightness
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....
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Relevant QEMU files:
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* `hw/arm/versatilepb.c`
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* `hw/misc/arm_sysctl.c`
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Relevant kernel files:
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* `arch/arm/boot/dts/versatile-pb.dts`
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* `drivers/leds/led-class.c`
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* `drivers/leds/leds-sysctl.c`
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=== Linux kernel hardening
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Make it harder to get hacked and easier to notice that you were, at the cost of some (small?) runtime overhead.
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==== CONFIG_FORTIFY_SOURCE
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Enable:
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....
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./build -C 'CONFIG_FORTIFY_SOURCE=y'
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....
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Test it out:
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....
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./run -F 'insmod /strlen_overflow.ko'
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....
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Detects the overflow:
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....
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<4>[ 3.136382] strlen_overflow: loading out-of-tree module taints kernel.
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<0>[ 3.139534] detected buffer overflow in strlen
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<4>[ 3.141318] ------------[ cut here ]------------
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....
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followed by a trace.
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=== Linux kernel testing
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https://stackoverflow.com/questions/3177338/how-is-the-linux-kernel-tested
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@@ -3836,22 +3734,112 @@ As a consequence:
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* it is possible to restore snapshots across boots, since they stay on the same image the entire time
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* it is not possible to use snapshots with <<initrd>> in our setup, since we don't pass `-drive` at all when initrd is enabled
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=== Educational hardware models
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=== Hardware models
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We have added and interacted with a few educational hardware models in QEMU.
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This section documents some interesting peripheral hardware models, specially simpler ones that are fun to learn.
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This is useful to learn:
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Studying them can teach you:
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* how to create new hardware models for QEMU. Overview: https://stackoverflow.com/questions/28315265/how-to-add-a-new-device-in-qemu-source-code
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* how the Linux kernel interacts with hardware
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To get started, have a look at the "Hardware device drivers" section under link:kernel_module/README.adoc[], and try to run those modules, and then grep the QEMU source code.
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==== platform_device
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==== Mainline hardware models
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This section documents hardware models present in the QEMU upstream.
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===== GPIO
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TODO: broken. Was working before we moved `arm` from `-M versatilepb` to `-M virt` around af210a76711b7fa4554dcc2abd0ddacfc810dfd4. Either make it work on `-M virt` if that is possible, or document precisely how to make it work with `versatilepb`, or hopefully `vexpress` which is newer.
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QEMU does not have a very nice mechanism to observe GPIO activity: https://raspberrypi.stackexchange.com/questions/56373/is-it-possible-to-get-the-state-of-the-leds-and-gpios-in-a-qemu-emulation-like-t/69267#69267
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The best you can do is to hack our link:build[] script to add:
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....
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HOST_QEMU_OPTS='--extra-cflags=-DDEBUG_PL061=1'
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....
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where link:http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0190b/index.html[PL061] is the dominating ARM Holdings hardware that handles GPIO.
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Then compile with:
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....
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./build -aa -b br2_gpio -c kernel_config_fragment/gpio -l
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....
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then test it out with:
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....
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/gpio.sh
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....
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Buildroot's Linux tools package provides some GPIO CLI tools: `lsgpio`, `gpio-event-mon`, `gpio-hammer`, TODO document them here.
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Those broke MIPS build in 2017-02: https://bugs.busybox.net/show_bug.cgi?id=10276 and so we force disable them in our MIPS build currently.
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===== LEDs
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TODO: broken when `arm` moved to `-M virt`, same as <<gpio>>.
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Hack QEMU's `hw/misc/arm_sysctl.c` with a printf:
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....
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static void arm_sysctl_write(void *opaque, hwaddr offset,
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uint64_t val, unsigned size)
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{
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arm_sysctl_state *s = (arm_sysctl_state *)opaque;
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switch (offset) {
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case 0x08: /* LED */
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printf("LED val = %llx\n", (unsigned long long)val);
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....
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and then rebuild with:
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....
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./build -aa -c kernel_config_fragment/leds -lq
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....
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But beware that one of the LEDs has a heartbeat trigger by default (specified on dts), so it will produce a lot of output.
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And then activate it with:
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....
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cd /sys/class/leds/versatile:0
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cat max_brightness
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echo 255 >brightness
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....
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Relevant QEMU files:
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* `hw/arm/versatilepb.c`
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* `hw/misc/arm_sysctl.c`
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Relevant kernel files:
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* `arch/arm/boot/dts/versatile-pb.dts`
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* `drivers/leds/led-class.c`
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* `drivers/leds/leds-sysctl.c`
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==== Fork hardware models
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This section documents hardware models added on link:https://github.com/cirosantilli/qemu[our fork of QEMU].
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These have been explicitly designed to be educational rather than model real existing hardware.
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===== platform_device
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This is an example of hardware coded into an ARM `-M versatilepb` SoC.
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Using this device now requires checking out to: https://github.com/cirosantilli/linux-kernel-module-cheat/tree/platform-device before building, it does not work on master.
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Using this device now requires checking out to the branch:
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....
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git checkout platform-device
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....
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before building, it does not work on master.
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The module itself can be found at: https://github.com/cirosantilli/linux-kernel-module-cheat/blob/platform-device/kernel_module/platform_device.c
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@@ -3894,7 +3882,7 @@ insmod /platform_device.ko
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==== gem5 educational hardware models
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TODO
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TODO get some working!
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http://gedare-csphd.blogspot.co.uk/2013/02/adding-simple-io-device-to-gem5.html
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