From: Stuart Henderson <stu@spacehopper.org>
Subject: Re: Fw: Compiling bsd.rd / bsd.update with custom kernel patches?
To: "requiem." <rqm@0xde501a7a.net>
Cc: tech@openbsd.org
Date: Thu, 19 Jun 2025 08:29:49 +0100

On 2025/06/18 20:06, requiem. wrote:
> I can and successfully have done it before a few times but the problem
> is that whenever I need to upgrade the system on -current the bugs
> return as non-patched "bsd" and "bsd.rd" / "bsd.upgrade" files get
> installed via the normal install process. I would then need to wait out
> the long boot on upgrade and first boot, re-patch and install the
> kernel in place, etc.

I would handle this by doing the upgrade differently. Basically follow
the steps from https://www.openbsd.org/faq/upgrade77.html#NoInstKern but
after untarring the sets, attempt to compile and install a GENERIC.MP
kernel from updated source (probably simpler on the machine itself
rather than another one). It won't always work (the newly untarred
binaries won't always work on the booted older kernel) but most of
the time it will, and the first stage will leave you with an updated
bsd and bsd.rd that you can boot (obviously with the extra delay)
as a fallback should you need it - though you're not likely to need
it very often.

> I have been trying to speed up this process by compiling the kernel on
> another machine running the same version. However I have not been too
> successful so I am asking for some guidance:
> 
> Here's what I would hope to achieve:
> - on the affected mac, run `sysupgrade -ns && pkg_update -u -Dsnap` and
>   not reboot
> - compile the patched bsd.rd and bsd.mp on another machine
> - swap out the mac's /bsd.upgrade with the patched bsd.rd as well
>   as /home/_sysupgrade/bsd.rd and /home/_sysupgrade/bsd.mp
> - hopefully then reboot the macbook and boot normally without getting
>   stuck for hours due to the acpi firmware bug it has
> 
> Here's what I tried:
> - on the mac: `sysupgrade -ns`
> - on the other machine:
> ```
> # patch < mypatch.diff
> # cd /sys/arch/amd64/compile/RAMDISK
> # make obj
> # make config
> # make
> # cp obj/bsd.gdb ~/bsd.rd.tocopy
> # cd /sys/arch/amd64/compile/GENERIC.MP
> # make obj
> # make config
> # make
> # cp obj/bsd.gdb ~/bsd.mp.tocopy
> ```
> - copy over the new `bsd.{rd,mp}.tocopy` to the Macbook over the lan
> 
> - on the mac again:
> ```
> # cp ~/bsd.rd.tocopy /bsd.upgrade
> # cp ~/bsd.rd.tocopy /home/_sysupgrade/bsd.rd
> # cp ~/bsd.mp.tocopy /home/_sysupgrade/bsd.mp
> # reboot
> ```
> 
> Here's what happens:
> 
> ```
> upgrade detected: switching to /bsd.upgrade
> boot> 
> booting sr0a:/bsd.upgrade [...]
> fchmod a-x sr0a/bsd.upgrade: failed
> entry point at 0x1001000
> 
> [machine reboots]
> ```
> 
> What am I doing wrong? How can I compile the ramdisk kernel only?

That's done as part of "make release", see release(8). It needs a built
base system as well though. Manual upgrade is probably a lot simpler
for this situation though.