linux-kernel - RE: [RFC] buildtar: add case for riscv architecture

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Date:   Fri, 20 Sep 2019 15:40:29 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     mail@...abindo.in
CC:     Anup Patel <Anup.Patel@....com>,
        Troy Benjegerdes <troy.benjegerdes@...ive.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject:     RE: [RFC] buildtar: add case for riscv architecture

On Tue, 17 Sep 2019 02:35:10 PDT (-0700), mail@...abindo.in wrote:
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Sunday, September 15, 2019 12:57 AM, Palmer Dabbelt <palmer@...ive.com> wrote:
>
>> On Sat, 14 Sep 2019 06:05:59 PDT (-0700), Anup Patel wrote:
>>
>> > > -----Original Message-----
>> > > From: linux-kernel-owner@...r.kernel.org <linux-kernel-
>> > > owner@...r.kernel.org> On Behalf Of Palmer Dabbelt
>> > > Sent: Saturday, September 14, 2019 6:30 PM
>> > > To: mail@...abindo.in
>> > > Cc: Troy Benjegerdes troy.benjegerdes@...ive.com; Paul Walmsley
>> > > paul.walmsley@...ive.com; aou@...s.berkeley.edu; linux-
>> > > riscv@...ts.infradead.org; linux-kernel@...r.kernel.org; linux-
>> > > kbuild@...r.kernel.org
>> > > Subject: Re: [RFC] buildtar: add case for riscv architecture
>> > > On Wed, 11 Sep 2019 05:54:07 PDT (-0700), mail@...abindo.in wrote:
>> > >
>> > > > > None of the available RiscV platforms that I’m aware of use compressed
>> > > > > images, unless there are some new bootloaders I haven’t 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
>> > > support.
>> > > 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
>> > > something.
>> > > 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.
>>
>
> Uncompressed vmlinux is already copied by default. This patch just adds the
> Image.gz into the archive as vmlinuz. But as you said, since the name vmlinuz is
> reserved for self extracting archives, should I keep the original name Image.gz ?

vmlinux is not the same as Image: vmlinux is an ELF file that can't be loaded 
directly by most bootloaders, Image is a mostly-flat binary with a small header 
that we're expecting can be booted by most bootloaders.