RE: [RFC] buildtar: add case for riscv architecture

From: Palmer Dabbelt
Date: Sat Sep 14 2019 - 15:28:01 EST

On Sat, 14 Sep 2019 06:05:59 PDT (-0700), Anup Patel wrote:

-----Original Message-----
From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-
owner@xxxxxxxxxxxxxxx> On Behalf Of Palmer Dabbelt
Sent: Saturday, September 14, 2019 6:30 PM
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Cc: Troy Benjegerdes <troy.benjegerdes@xxxxxxxxxx>; Paul Walmsley
<paul.walmsley@xxxxxxxxxx>; aou@xxxxxxxxxxxxxxxxx; linux-
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Subject: Re: [RFC] buildtar: add case for riscv architecture

On Wed, 11 Sep 2019 05:54:07 PDT (-0700), mail@xxxxxxxxxxxx wrote:
>> None of the available RiscV platforms that Iâm aware of use compressed
images, unless there are some new bootloaders I havenât seen yet.
> I noticed that default build image is Image.gz, which is why I thought its a
good idea to copy it into the tarball. Does such a copy not make sense at this
point ?

Image.gz can't be booted directly: it's just Image that's been compressed
with the standard gzip command. A bootloader would have to decompress
that image before loading it into memory, which requires extra bootloader
Contrast that with the zImage style images (which are vmlinuz on x86), which
are self-extracting and therefor require no bootloader support. The
examples for u-boot all use the "booti" command, which expects
uncompressed images.
Poking around I couldn't figure out a way to have u-boot decompress the
images, but that applies to arm64 as well so I'm not sure if I'm missing

If I was doing this, I'd copy over arch/riscv/boot/Image and call it
"/boot/image-${KERNELRELEASE}", as calling it vmlinuz is a bit confusing to
me because I'd expect vmlinuz to be a self-extracting compressed
executable and not a raw gzip file.

On the contrary, it is indeed possible to boot Image.gz directly using
U-Boot booti command so this patch would be useful.

Atish had got it working on U-Boot but he has deferred booti Image.gz
support due to few more dependent changes. May be he can share
more info.

Oh, great. I guess it makes sense to just put both in the tarball, then, as users will still need to use the Image format for now.