linux-kernel - Re: [PATCH] arm: Add support for ZSTD compressed kernel

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Date:   Thu, 6 Aug 2020 18:58:18 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
Cc:     nolange79@...il.com, linux-kernel@...r.kernel.org,
        Petr Malat <oss@...at.biz>, Kees Cook <keescook@...omium.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Sedat Dilek <sedat.dilek@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Nick Terrell <terrelln@...com>, Arnd Bergmann <arnd@...db.de>,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] arm: Add support for ZSTD compressed kernel

On Thu, Aug 6, 2020 at 6:22 PM Russell King - ARM Linux admin
<linux@...linux.org.uk> wrote:
>
> On Thu, Aug 06, 2020 at 05:46:50PM -0400, Peter Geis wrote:
> > Good Evening,
> >
> > I had attempted to get this working as well, but have run into
> > difficulties with both my implementation and yours as well.
> > My implementation was almost the same as yours, with the exception of
> > also changing:
> > @@ -303,7 +305,7 @@ restart: adr r0, LC1
> >
> >  #ifndef CONFIG_ZBOOT_ROM
> >   /* malloc space is above the relocated stack (64k max) */
> > - add r10, sp, #0x10000
> > + add r10, sp, #0x30000
> >  #else
> >   /*
> >   * With ZBOOT_ROM the bss/stack is non relocatable,
> >
> > On QEMU this implementation works fine.
> > However on bare metal tegra30, I get the following error:
> >
> > Jumping to kernel at:4861 ms
> >
> > C:0x80A000C0-0x8112BA40->0x8152C700-0x81C58080
> > Uncompressing Linux...
> >
> > ZSTD-compressed dstSize is too small
> >
> >  -- System halted
> >
> > The only difference between the bare metal test and the qemu test is
> > the zImage with appended dtb is packaged in the android boot format
> > for the bare metal test.
> > Otherwise it's exactly the same file.
>
> So it's relocating the compressed kernel and decompressor from
> 0x80A000C0-0x8112BA40 to 0x8152C700-0x81C58080 and then failing.
> Does the QEMU version also do similar?

Here is the output from QEMU, note boot doesn't work because this
image isn't for QEMU:

C:0x400100C0-0x4073B1E0->0x4152C600-0x41C57720
Uncompressing Linux... done, booting the kernel.

>
> On the off-hand, I'm not sure why it should fail.  I assume that
> you've tried the other decompressors and they work fine on the
> same setups?

Correct, all other compressors work.
ZSTD is handy for arm because size and speed are both important.

>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!