git: fe0c839e2cb3 - stable/13 - kboot: Add readme
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Date: Tue, 24 Jan 2023 22:13:40 UTC
The branch stable/13 has been updated by imp: URL: https://cgit.FreeBSD.org/src/commit/?id=fe0c839e2cb30f057d60ebb724a778bf13c503c9 commit fe0c839e2cb30f057d60ebb724a778bf13c503c9 Author: Warner Losh <imp@FreeBSD.org> AuthorDate: 2022-12-03 19:48:16 +0000 Commit: Warner Losh <imp@FreeBSD.org> CommitDate: 2023-01-24 21:49:41 +0000 kboot: Add readme Document how to test kboot and how to build a initrd. Sponsored by: Netflix (cherry picked from commit 59cbe840cffcd5513e1d3b8736fb6c0d10945ab2) --- stand/kboot/README | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 48 insertions(+) diff --git a/stand/kboot/README b/stand/kboot/README new file mode 100644 index 000000000000..ad390a023bb9 --- /dev/null +++ b/stand/kboot/README @@ -0,0 +1,48 @@ +So to make a Linux initrd: + +(1) mkdir .../initrd +(2) mkdir -p .../initrd/boot/defaults +(3) cd src/stand; make install DESTDIR=.../initrd +(4) Copy kernel to .../initrd/boot/kernel +(5) cd .../initrd +(6) cp boot/loader.kboot init +(7) find . | sort | cpio -o -H newc | gzip > /tmp/initrd.cpio +(8) download or build your linux kernel +(9) qemu-system-x86_64 -kernel ~/vmlinuz-5.19.0-051900-generic \ + -initrd /tmp/initrd.cpio \ + -m 256m -nographic \ + -monitor telnet::4444,server,nowait -serial stdio \ + -append "console=ttyS0" + (though you may need more than 256M of ram to actually boot FreeBSD and do + anything interesting with it and the serial console to stdio bit hasn't + been the most stable recipe lately). + +Notes: +For #6 you might need to strip loader.kboot if you copy it directly and don't + use make install. +For #7 the sort is important, and you may need LC_ALL=C for its invocation +For #7 gzip is but one of many methods, but it's the simplest to do. +For #9, this means we can automate it using methods from + src/tools/boot/rootgen.sh when the time comes. +#9 also likely generalizes to other architectures +For #8, see https://kernel.ubuntu.com/~kernel-ppa/mainline/ to download + a kernel suitable for testing... For arm, I've been using the + non 64k page kernels and 5.19 seems to not suck. + +aarch64: +qemu-system-aarch64 -m 1024 -cpu cortex-a57 -M virt \ + -kernel ~/linuxboot/arm64/kernel/boot/vmlinuz-5.19.0-051900-generic \ + -initrd ~/linuxboot/arm64/initrd.img -m 256m -nographic \ + -monitor telnet::4444,server,nowait -serial stdio \ + -append "console=ttyAMA0" + +General + +Add -g -G to have gdb stop and wait for the debugger. This is useful for +debugging the trampoline (hbreak will set a hardware break that's durable across +code changes). If you set the breakpoint for the trampoline and it never hits, +then there's likely no RAM there and you got the PA to load to wrong. When +debugging the trampiline and up to that, use gdb /boot/loader. When debugging +the kernel, use kernel.full to get all the debugging. hbreak panic() is useful +on the latter since you'll see the original panic, not the panic you get from +there not being an early console.