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Subject: Re: 11.0-RELEASE tier level for arm64/aaarch64 and the officially
 built arm/armv6 variants?
From: Tim Kientzle <tim@kientzle.com>
In-Reply-To: <CABx9NuTFobc1e4UxsLSPKLTtMgt37QDgR99xHhkdCkc7qPHCxA@mail.gmail.com>
Date: Sun, 25 Sep 2016 08:57:18 -0700
Cc: Warner Losh <imp@bsdimp.com>, freebsd-arm <freebsd-arm@freebsd.org>,
 FreeBSD-STABLE Mailing List <freebsd-stable@freebsd.org>
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To: Russell Haley <russ.haley@gmail.com>
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> On Sep 25, 2016, at 12:13 AM, Russell Haley <russ.haley@gmail.com> wrote:
> 
>> We can't easily do away with ubldr if we want to support tunables, kernel
>> modules loaded at boot time and a few other nifty features like nextboot.
> 
> Are these things not in standard loader? Should they be?

"ubldr" *is* the standard loader.  It's built from (mostly) the same
source as loader(8) used on x86.  But, where loader(8) uses the BIOS
interface to access the disk, "ubldr" uses the U-Boot ABI to
access the disk.

FreeBSD's current boot sequence for ARM boards looks like this:
   * U-Boot loads ubldr
   * ubldr uses U-Boot to access disk and console
   * ubldr loads the kernel, kernel modules, and sets kernel tunables

To replace U-Boot, bare box would either have to duplicate
everything ubldr does (which is a lot) or would have to provide
the U-Boot ABI (or something similar) so that ubldr can provide
the final boot stage.

Tim