Re: [BISECTED] kexec issue with v4.15-rc on N8x0

[Russell King - ARM Linux <linux@armlinux.org.uk>]

On Tue, Jan 23, 2018 at 12:06:54AM +0200, Aaro Koskinen wrote:
> Hi,
> 
> On Mon, Jan 15, 2018 at 10:15:08AM -0800, Tony Lindgren wrote:
> > * Aaro Koskinen <aaro.koskinen@iki.fi> [180111 11:48]:
> > > When booting v4.15-rc kernel with kexec (kexec-tools 2.0.16) on N8x0, I get:
> > > 
> > >     Uncompressing Linux... done, booting the kernel.
> > >     no ATAGS support: can't continue
> > > 
> > > v4.14 kernel works OK.
> > > 
> > > I bisected this to:
> > > 
> > > commit c772568788b5f0cbaac7c8d4111d7173bfc90673
> > > Author: Russell King <rmk+kernel@armlinux.org.uk>
> > > Date:   Thu Sep 21 18:10:19 2017 +0100
> > > 
> > >     ARM: add additional table to compressed kernel
> > > 
> > > If I revert the commit, kexec booting starts to work. Interesting,
> > > the patch mentions "This is necessary for correct behaviour of kexec.",
> > > so I wonder what could be wrong...
> > 
> > So care to post what you get if you load with kexec -d -l options
> > before and after this commit?
> 
> See below. I guess the interesting part is the "zImage has tags" with the
> bad kernel.
> 
> Bad (plain v4.15-rc9)
> ---------------------
> kernel: 0xb6a25008 kernel_size: 0x3ce605
> MEMORY RANGES
> 0000000080000000-0000000087ffffff (0)
> zImage header: 0x016f2818 0x00000000 0x003c59d0
> zImage size 0x3c59d0, file size 0x3ce605

This looks like you've appended a DTB blob to the zImage as the file
is larger than the zImage says it should be.

> zImage has tags
>   offset 0x00003be0 tag 0x5a534c4b size 8

Right, so this says that this is a "modern" kernel that's being loaded
with the additional tags in that tell kexec how much space the
decompressed kernel requires.

> kernel image size: 0x00c5c6ec

and it requires this amount of space.

> kexec_load: entry = 0x80008000 flags = 0x280000
> nr_segments = 2
> segment[0].buf   = 0xb6a25008
> segment[0].bufsz = 0x3c59d0
> segment[0].mem   = 0x80008000
> segment[0].memsz = 0x3c6000

This is the kernel, with the appended dtb removed.

> segment[1].buf   = 0x1ed52b8
> segment[1].bufsz = 0x8c35
> segment[1].mem   = 0x80c66000
> segment[1].memsz = 0x9000

This is the DTB, placed out of the way from the kernel (the highest
address the kernel will use while decompressing is 0x00c5c6ec +
0x80008000.  Everything here looks correct.

> [    4.850341] kexec_core: Starting new kernel
> [    4.854766] Bye!
> 
> (kernel fails to boot)
> 
> Good (v4.15-rc9 and c772568788b5f0cbaac7c8d4111d7173bfc90673 reverted)
> -----------------------------
> kernel: 0xb6999008 kernel_size: 0x3ce9bd
> MEMORY RANGES
> 0000000080000000-0000000087ffffff (0)
> zImage header: 0x016f2818 0x00000000 0x003c5d88
> zImage size 0x3c5d88, file size 0x3ce9bd
> kexec_load: entry = 0x80008000 flags = 0x280000
> nr_segments = 2
> segment[0].buf   = 0xb6999008
> segment[0].bufsz = 0x3c5d88
> segment[0].mem   = 0x80008000
> segment[0].memsz = 0x3c6000

Here we have the same thing for the kernel.

> segment[1].buf   = 0x14192b8
> segment[1].bufsz = 0x8c35
> segment[1].mem   = 0x812e7000
> segment[1].memsz = 0x9000

Here, the DTB is placed much further away.

Unfortunately, with this debug, it's still not possible to debug this.

I'm rather sick of these image placement issues, there seems to be no
solution here that works for everyone, no matter how hard I try with
my knowledge of how the ARM kernel decompresses and places itself.

It really doesn't help that it took ages for the kexec-tools patches
to get merged, and when they did get merged, the wrong patch set was
taken.  Consequently, the debug above does not match my local source
tree, and neither does the code.

Sorry, but I'm afraid I can't debug this at the moment.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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