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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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run: Ctrl+C works and gets passed to guest... at last!
readme: document graphics failures on arm and aarch64 further.
This commit is contained in:
Ciro Santilli
223
README.adoc
223
README.adoc
@@ -162,6 +162,124 @@ After this, to start using Docker again will you need another:
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./rundocker setup
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....
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=== Text mode
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By default, we show the serial console directly on the current terminal, without opening a QEMU window.
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Quit QEMU immediately:
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....
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Ctrl-A X
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....
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https://superuser.com/questions/1087859/how-to-quit-the-qemu-monitor-when-not-using-a-gui
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Alternative methods:
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* `/poweroff.out`. Not immediate, and sometimes you can't do it, e.g. kernel panic. Furthermore, it does not work for ARM: <<arm-shutdown>>
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* `echo quit | ./qemumonitor`
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* `Ctrl-A C` then `quit`
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* `pkill qemu`
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Toggle between QEMU monitor and the shell:
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....
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Ctrl-A C
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....
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* http://stackoverflow.com/questions/14165158/how-to-switch-to-qemu-monitor-console-when-running-with-curses
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* https://superuser.com/questions/488263/how-to-switch-to-the-qemu-control-panel-with-nographics
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But doing:
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....
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echo quit | ./qemumonitor
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....
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is generally more practical since you can use host shell functionality like shell history.
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Getting everything to work requires careful choice of QEMU command line options:
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* https://stackoverflow.com/questions/49716931/how-to-run-qemu-with-nographic-and-monitor-but-still-be-able-to-send-ctrlc-to/49751144#49751144
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* https://unix.stackexchange.com/questions/167165/how-to-pass-ctrl-c-to-the-guest-when-running-qemu-with-nographic/436321#436321
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TODO: if you hit `Ctrl-C` several times while `arm` or `aarch64` are booting, after boot the userland shell does not show any updates when you type. Why?
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=== Graphic mode
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Enable graphic mode:
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....
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./run -x
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....
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Text mode is the default due to the following considerable advantages:
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* copy and paste commands and stdout output to / from host
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* get full panic traces when you start making the kernel crash :-) See also: https://unix.stackexchange.com/questions/208260/how-to-scroll-up-after-a-kernel-panic
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* have a large scroll buffer, and be able to search it, e.g. by using tmux on host
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* one less window floating around to think about in addition to your shell :-)
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* graphics mode has only been properly tested on `x86_64`.
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Text mode has the following limitations over graphics mode:
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* you can't see graphics such as those produced by <<x11>>
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* very early kernel messages such as `early console in extract_kernel` only show on the GUI, since at such early stages, not even the serial has been setup.
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==== Graphic mode arm
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TODO: how to see the terminal on the graphic window, just like happens on x86?
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arm shows a window which contains boot messages, but the shell is only visible on the terminal.
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Also if we do:
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....
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cat /dev/urandom > /dev/fb0
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....
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the screen fills up with random colors, so that screen is working somehow.
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Using `-nographic` removes that screen, but why would we want to do that? TODO Ideally, all archs would show both the terminal and the graphical window.
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==== Graphic mode aarch64
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TODO even though we don't pass `-nographic`, `aarch64` does not get a graphic window like `arm`, why?
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=== Automatic startup commands
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When debugging a module, it becomes tedious to wait for build and re-type:
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....
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/modulename.sh
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....
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every time.
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To automate that, use the methods described at: <<init>>
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=== Message control
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We use `printk` a lot, and it shows on the QEMU terminal by default. If that annoys you (e.g. you want to see stdout separately), do:
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....
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dmesg -n 1
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....
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See also: https://superuser.com/questions/351387/how-to-stop-kernel-messages-from-flooding-my-console
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When in <<graphic-mode>>, you can scroll up a bit on the default TTY with:
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....
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Shift-PgUp
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....
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but I never managed to increase that buffer:
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* https://askubuntu.com/questions/709697/how-to-increase-scrollback-lines-in-ubuntu14-04-2-server-edition
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* https://unix.stackexchange.com/questions/346018/how-to-increase-the-scrollback-buffer-size-for-tty
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The superior alternative is to use text mode or a telnet connection.
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=== Module documentation
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....
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@@ -307,103 +425,6 @@ Remember that if you forcibly turn QEMU off without `sync` or `poweroff` from in
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When booting from <<initrd>> however without a disk, persistency is lost.
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=== Message control
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We use `printk` a lot, and it shows on the QEMU terminal by default. If that annoys you (e.g. you want to see stdout separately), do:
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....
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dmesg -n 1
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....
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See also: https://superuser.com/questions/351387/how-to-stop-kernel-messages-from-flooding-my-console
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When in <<graphic-mode>>, you can scroll up a bit on the default TTY with:
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....
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Shift-PgUp
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....
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but I never managed to increase that buffer:
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* https://askubuntu.com/questions/709697/how-to-increase-scrollback-lines-in-ubuntu14-04-2-server-edition
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* https://unix.stackexchange.com/questions/346018/how-to-increase-the-scrollback-buffer-size-for-tty
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The superior alternative is to use text mode or a telnet connection.
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=== Graphic mode
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By default, we show the serial console directly on the current terminal, without opening a QEMU window.
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To enable graphic mode, use:
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....
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./run -x
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....
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Text mode is the default due to the following considerable advantages:
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* copy and paste commands and stdout output to / from host
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* get full panic traces when you start making the kernel crash :-) See also: https://unix.stackexchange.com/questions/208260/how-to-scroll-up-after-a-kernel-panic
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* have a large scroll buffer, and be able to search it, e.g. by using tmux on host
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* one less window floating around to think about in addition to your shell :-)
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* graphics mode has only been properly tested on `x86_64`.
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Text mode has the following limitations over graphics mode:
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* you can't see graphics such as those produced by <<x11>>
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* very early kernel messages such as `early console in extract_kernel` only show on the GUI, since at such early stages, not even the serial has been setup.
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Both good and bad:
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* `Ctrl-C` kills the host emulator instead of sending SIGINT to the guest process.
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+
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On one hand, this provides an easy way to quit QEMU.
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+
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On the other, we are unable to easily kill the foreground process, which is specially problematic when it is something like an infinite loop. and not sent to guest processes.
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+
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It is also hard to enter the monitor for the same reason:
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+
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--
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* http://stackoverflow.com/questions/14165158/how-to-switch-to-qemu-monitor-console-when-running-with-curses
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* https://superuser.com/questions/488263/how-to-switch-to-the-qemu-control-panel-with-nographics
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* https://superuser.com/questions/1087859/how-to-quit-the-qemu-monitor-when-not-using-a-gui/1211516#1211516
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--
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+
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This behaviour is caused by the `-monitor` option: https://unix.stackexchange.com/questions/167165/how-to-pass-ctrl-c-to-the-guest-when-running-qemu-with-nographic/436321#436321
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+
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TODO: find a solution, that allows us to use both `-monitor` and send `Ctrl-C`: https://stackoverflow.com/questions/49716931/how-to-run-qemu-with-nographic-and-monitor-but-still-be-able-to-send-ctrlc-to
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+
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Our workaround is:
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+
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....
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./qemumonitor
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....
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+
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`sendkey ctrl-c` does not work on the text terminal either.
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+
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This is however fortunate when running QEMU with GDB, as the `Ctrl-C` reaches GDB and breaks.
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* Not everything generates interrupts, only the final enter.
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+
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This makes things a bit more reproducible, since the microsecond in which you pressed a key does not matter.
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+
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But on the other hand maybe you are interested in observing the interrupts generated by key presses.
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=== arm graphic mode
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TODO: how to see the terminal on the graphic window, just like happens on x86?
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=== Automatic startup commands
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When debugging a module, it becomes tedious to wait for build and re-type:
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....
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/modulename.sh
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....
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every time.
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To automate that, use the methods described at: <<init>>
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=== Kernel command line parameters
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Bootloaders can pass a string as input to the Linux kernel when it is booting to control its behaviour, much like the `execve` system call does to userland processes.
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@@ -1471,14 +1492,6 @@ A friend told me this but I haven't tried it yet:
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* `xf86-video-modesetting` is likely the missing ingredient, but it does not seem possible to activate it from Buildroot currently without patching things.
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* `xf86-video-fbdev` should work as well, but we need to make sure fbdev is enabled, and maybe add some line to the `Xorg.conf`
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Also if I do:
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....
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cat /dev/urandom > /dev/fb0
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....
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the screen fills up with random colors, so I think it can truly work.
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=== X11 MIPS
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Haven't tried it, doubt it will work out of the box! :-)
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4
run
4
run
@@ -184,6 +184,7 @@ ${debug_vm} \
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'${buildroot_out_dir}/host/usr/bin/qemu-system-${arch}' \\
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-gdb tcp::1234 \\
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-m '${memory}' \\
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-serial mon:stdio \\
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-monitor telnet::45454,server,nowait \\
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-netdev user,hostfwd=tcp::45455-:45455,hostfwd=tcp::45456-:22,id=net0 \\
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-smp '${cpus}' \\
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@@ -237,7 +238,6 @@ ${qemu_common} \
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-device rtl8139,netdev=net0 \\
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-dtb '${images_dir}/versatile-pb.dtb' \\
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-kernel '${images_dir}/zImage' \\
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-serial stdio \\
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${extra_flags} \
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"
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;;
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@@ -257,8 +257,6 @@ ${qemu_common} \
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-cpu cortex-a57 \\
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-device virtio-net-device,netdev=net0 \\
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-kernel '${images_dir}/Image' \\
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-nographic \\
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-serial stdio \\
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${extra_flags} \
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"
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;;
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