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https://github.com/cirosantilli/linux-kernel-module-cheat.git
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254c8bf42e
Semi automated conversion, in part because Pandoc is kind of buggy for adoc:
Some of the commands were along the lines:
for f in *.md; do pandoc --atx-headers --base-header-level=3 -o ${f%.md}.adoc --wrap=none $f; done
sed -Ei '/\[\[.*\]\]/d' *.adoc
while read -r f; do cat $f; echo; done <f >g
41 lines
1.3 KiB
Plaintext
41 lines
1.3 KiB
Plaintext
=== QEMU user mode
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This has nothing to do with the Linux kernel, but it is cool:
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....
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sudo apt-get install qemu-user
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./build -a arm
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cd buildroot/output.arm~/target
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qemu-arm -L . bin/ls
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....
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This uses QEMU's user-mode emulation mode that allows us to run cross-compiled userland programs directly on the host.
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The reason this is cool, is that `ls` is not statically compiled, but since we have the Buildroot image, we are still able to find the shared linker and the shared library at the given path.
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In other words, much cooler than:
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....
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arm-linux-gnueabi-gcc -o hello -static hello.c
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qemu-arm hello
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....
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It is also possible to compile QEMU user mode from source with `BR2_PACKAGE_HOST_QEMU_LINUX_USER_MODE=y`, but then your compilation will likely fail with:
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....
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package/qemu/qemu.mk:110: *** "Refusing to build qemu-user: target Linux version newer than host's.". Stop.
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....
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since we are using a bleeding edge kernel, which is a sanity check in the Buildroot QEMU package.
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Anyways, this warns us that the userland emulation will likely not be reliable, which is good to know. TODO: where is it documented the host kernel must be as new as the target one?
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GDB step debugging is also possible with:
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....
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qemu-arm -g 1234 -L . bin/ls
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../host/usr/bin/arm-buildroot-linux-uclibcgnueabi-gdb -ex 'target remote localhost:1234'
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....
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TODO: find source. Lazy now.
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