Re: [Qemu-devel] [Qemu-ppc] [PATCH] ppc/pnv: Generate phandle for the "interrupt-parent" property

[David Gibson]

On Wed, Jul 24, 2019 at 08:25:04PM +0530, Amol Surati wrote:
> On Wed, Jul 24, 2019 at 06:57:30PM +1000, David Gibson wrote:
> > On Wed, Jul 24, 2019 at 09:11:54AM +0200, Cédric Le Goater wrote:
> > > On 24/07/2019 05:23, David Gibson wrote:
> > > > On Tue, Jul 23, 2019 at 11:01:38AM +0200, Cédric Le Goater wrote:
> > > >> Devices such as the BT or serial devices require a valid
> > > >> "interrupt-parent" phandle in the device tree and it is currently
> > > >> empty (0x0). It was not a problem until now but since OpenFirmare
> > > >> started using a recent libdft (>= 1.4.7), petitboot fails to boot the
> > > >> system image with error :
> > > >>
> > > >>    dtc_resize: fdt_open_into returned FDT_ERR_BADMAGIC
> > > >>
> > > >> Provide a phandle for the LPC bus.
> > > >>
> > > >> Suggested-by: Greg Kurz <address@hidden>
> > > >> Signed-off-by: Cédric Le Goater <address@hidden>
> > > > 
> > > > I've applied this, since it looks to be correct.
> > > > 
> > > > But.. can you connect the dots for me in how this being missing
> > > > results in a BADMAGIC error??
> > > 
> > > Some binary called by petitboot segfaults when trying to kexec an image 
> > > on 
> > > a system with a bogus DT (generated by QEMU). I don't know exactly which 
> > > one 
> > > as I only see the error message above and the segv message in dmesg
> > 
> > Ok, I'm still not seeing how that gets you to a BADMAGIC error.
> 
> If I may interject, as this patch is related to the qemu bug:
> https://bugs.launchpad.net/qemu/+bug/1826827.
> 
> The error is printed by dtc_resize in kexec.c from kexec-lite
> (antonblanchard/kexec-lite).
> 
> There are two places where dtc_resize is called -
> (1) initialize_fdt, when kexec is passed a dtb file.
> (2) fdt_from_fs, when kexec must make dtc read /proc/device-tree to form
>     a dtb.
> 
> If initialize_fdt is called with a file which is an invalid dtb, the
> dtc_resize prints the FDT_ERR_BADMAGIC error.
> 
> Bug# 1826827 shows that dtc is one application that does
> crash, although through the firing of an assertion, in the absence of
> the mentioned properties. (fix to avoid the crash already checked into
> dtc upstream, commit 8f69567622; to be released with dtc-v1.5.1).
> 
> Assuming that the crashing app (it is not known here what it is) is
> supposed to create a dtb for kexec, and its crash leaves behind an
> incomplete/invalid dtb file, the initialize_fdt might receive an invalid
> dtb.

Ok, thanks.  That's what I was after.

> 
> 
> Another possibility for that error exists within the fdt_from_fs function,
> but that needs a version of kexec-lite at least 5 years old, which is
> unlikely to be used here I guess.
> 
> 
> 
> If this patch fixes both the crash and the error "dtc_resize: ....",
> it is likely that dtc (or anything else which depends on libfdt) was the
> cause of the crash, with dtc/libfdt version being < g8f69567622.
> 
> 
> Thanks,
> -amol
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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