[Qemu-devel] [Bug 1826827] Re: dtc crash; pnv_dt_serial cannot find lpc's phandle

[Amol Surati]

> Btw, I'm assuming where you say...
My bad. Yes, you are correct. The problem is seen when decompiling the blob to 
source.


> 1) The powernv machine in qemu is attempting to use a phandle for node
> that doesn't have one.

True.


> 2) dtc is crashing with an assertion - that shouldn't happen, even on bad
> input it should error out rather than crashing. The problem also occurs
> with current upstream dtc - I'll try to investigate this.

The assertion says that "if dtc is trying to get a node by its phandle,
and if the input phandle is 0 or -1, then we better be processing
plugins, as that is the only mode where we allow such values for a
phandle."


If one removes the specific assertion which is triggered, the crash is avoided. 
Then, dtc prints
this (relevant) message before exiting:


"Warning (interrupts_property): 
/address@hidden/address@hidden/address@hidden:interrupt-parent: Bad phandle"


The message confirms qemu's inability to set the interrupt-parent of 
address@hidden to the correct, expected value. Depending on the point of view, 
that warning can be considered as the error that you want dtc to print 
(although dtc, instead of stopping at this warning, continues ahead instead, 
and generates a dts with interrupt-parent of that serial device set to 0).


When one looks at that generated dts source, two other siblings of 
address@hidden, address@hidden and address@hidden are found, which have the 
correct value for their interrupt-parent property. A bit of debugging showed 
that these two devices are populated by the skiboot firmware (and not by qemu).

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https://bugs.launchpad.net/bugs/1826827

Title:
  dtc crash; pnv_dt_serial cannot find lpc's phandle

Status in QEMU:
  New

Bug description:
  Qemu version:
  QEMU emulator version 4.0.50 (v4.0.0-142-ge0fb2c3d89)
  Copyright (c) 2003-2019 Fabrice Bellard and the QEMU Project developers

  dtc version:
  Version: DTC 1.5.0-g5c3513f6

  -------------------------------------------------------------------------
  pnv_dt_serial has a line which is supposed to set the interrupt-parent of the 
"address@hidden" node to the phandle of "address@hidden".

  To that end, it calls fdt_get_phandle as shown below:
  _FDT((fdt_setprop_cell(fdt, node, "interrupt-parent", fdt_get_phandle(fdt, 
lpc_off))));

  The function fdt_get_phandle fails to find the property "phandle" (or
  "linux,phandle") for the lpc node. Consequently, pnv_dt_serial sets
  the interrupt-parent to 0.

  Now boot the qemu-system-ppc64 powernv machine, and extract the fdt by
  using the qemu monitor's pmemsave command, taking help of the OPAL
  firmware's messages to locate the fdt in the physical ram.

  qemu-system-ppc64 -m 1g -machine powernv,num-chips=1 \
  -cpu power9 -smp 2,cores=2,threads=1 -accel tcg,thread=multi \
  -kernel ./vmlinux \
  -append 'disable_radix' \
  -serial mon:stdio -nographic -nodefaults

  The kernel vmlinux contains nothing but a single instruction which
  loops infintely, so that we can gather OPAL's messages, especially the
  one below:

  [    0.168845963,5] INIT: Starting kernel at 0x20000000, fdt at
  0x304b0b70 14404 bytes

  Once the fdt is dumped to a file, run the following:

  'dtc -O dtb -I dts -o out.dts dtb'

  After a few warnings, the dtc application crashes because an assertion
  was fired.

  out.dts: Warning (unit_address_vs_reg): /address@hidden/address@hidden: node 
has a unit name, but no reg property
  out.dts: Warning (simple_bus_reg): /address@hidden/address@hidden: missing or 
empty reg/ranges property
  out.dts: Warning (avoid_unnecessary_addr_size): /ibm,opal: unnecessary 
#address-cells/#size-cells without "ranges" or child "reg" property
  out.dts: Warning (unique_unit_address): /address@hidden: duplicate 
unit-address (also used in node /address@hidden)
  out.dts: Warning (chosen_node_stdout_path): /chosen:linux,stdout-path: Use 
'stdout-path' instead
  dtc: livetree.c:575: get_node_by_phandle: Assertion `generate_fixups' failed.
  Aborted (core dumped)

  The assertion is fired because get_node_by_phandle receives a phandle
  value of 0, which is unexpected, unless fixups are needed (They are
  not, when running the dtc command).

  Back inside pnv_dt_serial, if the line that sets "interrupt-parent"
  for the serial device node is commented out, the dtc crash is
  prevented. Looking at hw/ppc/e500.c, it takes care of allocating
  necessary phandle values in the nodes, so a similar method can be
  adopted for powernv.

  The dtb is attached.

  Edit: Add version, Correct filenames.

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