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readme: add an awesome and simple qemu hack

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Ciro Santilli
2018-09-12 12:35:19 +01:00
parent 1669470dd6
commit 5e83660e86
1 changed files with 71 additions and 59 deletions
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130
README.adoc
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@@ -160,65 +160,6 @@ All available modules can be found in the link:packages/kernel_modules/[`kernel_
See also: <<quit-qemu-from-text-mode>>.
Now try to modify link:packages/kernel_modules/hello.c[] to contain:
....
pr_info("hello init hacked\n");
....
and then rebuild the kernel modules and re-run to see it take effect:
....
./build --kernel-modules
./run -F 'insmod /hello.ko'
....
Congratulations, you are now officially a kernel module hacker!
The reboot after rebuild is annoying. We don't have a perfect solution for it yet, but there are some ideas cooking at: <<gem5-restore-new-script>>.
Not satisfied with kernel modules? OK then, let's hack up the <<linux-kernel-entry-point,entry point of the>> Linux kernel itself.
Open the file `submodules/linux/init/main.c` on your text editor, find the `start_kernel` function, and then add there a:
....
pr_info("I'VE HACKED THE LINUX KERNEL!!!");
....
Then rebuild the Linux kernel and reboot:
....
./build && ./run
....
and, surely enough, your message has appeared at the beginning of the boot.
So you are now officially a kernel hacker, way to go!
Not satisfied with mere software? OK then, let's hack up the QEMU entry point.
First find it with GDB:
....
./run --debug-vm
....
which leaves us at `submodules/qemu/vl.c`, so hack up the `main` there with:
....
puts("I'VE HACKED QEMU");
....
and as usual rebuild and re-run:
.....
./build-qemu && ./run
.....
and once again, there is your message.
You have now gone from newb to hardware hacker in a mere 15 minutes, your rate of progress is truly astounding!!!
I now urge you to read the following sections which contain widely applicable information:
* <<default-command-line-arguments>>
@@ -269,6 +210,77 @@ hello /root/.profile
│(gdb)
....
==== Your first kernel hack
Modify link:packages/kernel_modules/hello.c[] to contain:
....
pr_info("hello init hacked\n");
....
and then rebuild the kernel modules and re-run to see it take effect:
....
./build --kernel-modules
./run -F 'insmod /hello.ko'
....
Congratulations, you are now officially a kernel module hacker!
The reboot after rebuild is annoying. We don't have a perfect solution for it yet, but there are some ideas cooking at: <<gem5-restore-new-script>>.
Not satisfied with kernel modules? OK then, let's hack up the <<linux-kernel-entry-point,entry point of the>> Linux kernel itself.
Open the file:
....
vim submodules/linux/init/main.c
....
and find the `start_kernel` function, then add there a:
....
pr_info("I'VE HACKED THE LINUX KERNEL!!!");
....
Then rebuild the Linux kernel and reboot:
....
./build && ./run
....
and, surely enough, your message has appeared at the beginning of the boot.
So you are now officially a kernel hacker, way to go!
Not satisfied with mere software? OK then, let's hack up the QEMU x86 CPU identification:
....
vim submodules/qemu/target/i386/cpu.c
....
and modify:
....
.model_id = "QEMU Virtual CPU version " QEMU_HW_VERSION,
....
to contain:
....
.model_id = "QEMU Virtual CPU version HACKED " QEMU_HW_VERSION,
....
then as usual rebuild and re-run:
.....
./build-qemu && ./run -F 'grep "model name" /proc/cpuinfo'
.....
and once again, there is your message: QEMU communicated it to the Linux kernel, which printed it out.
You have now gone from newb to hardware hacker in a mere 15 minutes, your rate of progress is truly astounding!!!
==== About the QEMU Buildroot setup
link:https://en.wikipedia.org/wiki/Buildroot[Buildroot] is a set of `make` scripts that downloads from source and compiles compatible versions of: