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[Qemu-devel] GSoC 2015 (Mac OS 9 support) report, week 2

From: Alexander Graf
Subject: [Qemu-devel] GSoC 2015 (Mac OS 9 support) report, week 2
Date: Wed, 13 May 2015 00:35:18 +0200

[This Week]
  - Investigate MOL device tree further
    - <Mark> There is also an interesting dump of what seems to be a MOL tree
      at http://josejx.net/mol/mol-stable/mollib/oftrees/oftree.nw.old (which
      has a commented out entry for "AAPL,debug" set to -1). The interesting
      parts I see here are the "interrupt-controller" node in /chosen and
      various additional names in the "compatible" property for various
  - Progress past quiesce() client interface call
    - At the moment, this function simply closes all USB devices (`usb_exit()`)
      and sets the Instruction and Data Address Translation bits in the MSR
      (@agraf: does this cause any side effects?). The stack diagram shows no
      arguments or return values, and none of the other `ciface` functions make
      any modifications to the stack other than their arguments or return
    - Looks like `quiesce` either hangs on `mtmsr` or makes a jump out of the
    - MSR.IR and MSR.DR enable paging for instructions and data respectively.
      IIRC we disable paging when quiesce gets called because it's the last
      call that Linux runs before it executes non-OF aware code IIRC.
    - Try to run qemu with -d in_asm,cpu,int -D log and check where the code
      execution hangs :). There's a good chance we're already in the Mac OS 9
    - It would appear that execution has branched off into invalid memory.
      invalid/unsupported opcode: 00 - 00 - 00 (00000000) 00f03000 0     IN:
      0x00f03000:  .long 0x0
    - Awesome. What code gets executed before that? Maybe we shouldn't turn off
    - Actually looking at the code, the MSR IR/DR part is surround by a #if 0
      ... #endif pair... maybe something in usb_exit() is breaking things?
      Possibly try removing it temporarily?
  - Patch: Copyright string
  - Patch: RTAS node

[Next Week]
  - Remove extraneous "interrupts" property from /pci/mac-io
    - I'm having trouble tracking down where the property is actually being
      set. The mac-io devices are defined in drivers/pci_database.c, but the
      pci_dev_t struct (drivers/pci_database.h) doesn't appear to have an
      interrupts field. Much of the mac-io related functionality is defined in
      drivers/macio.c, but there's no mention of interrupts there so I'm kind
      of at a loss.
  - Test and debug boot script loader

[Long Term]
  - Continue updating project log
  - Create and send patches
    - [ ] Patch: Boot script loader
    - [ ] ROM node
  - Enable debugging in MOL
    - The installation is now broken after a failed make. Tried reinstalling
      from Zypper but it couldn't find the config files -- do they have to be
      added manually?
    - The config files are at a different location when you compile manually,
      but I don't remember where everything was :). Just run mol with strace,
      it will tell you where it's looking for things. The current ones should
      be somewhere in /etc.

  - Try to set AAPL,Debug in /
    - <mark> Did this have any effect in the end? Note that the casing above is
      incorrect and the property name should be "AAPL,debug".
    - This does work, it dumps most system calls to the output. Still looking
      for an actual cause for the error.
    - @cormacobrien2 That sounds great! Errors can sometimes be subtle, e.g.
      returning a wrong value rather than a missing value so it would be good
      to see the output. Does it run in -nographic mode so the output can be
      pasted into a github gist (similar to as you did for the OS 9 boot
    - @markcaveayland Here's a gist with the output log. Most of the relevant
      info is at the bottom, it's quite verbose. https://gist.github.com
    - @cormacobrien2 Hmmm that's interesting - it's complaining about the
      "interrupts" property on the macio device.  (goes and digs)  According to
      the copies of the g3beige and g4 device trees that I have here (and
      indeed the tree at http://josejx.net/mol/mol-
      stable/mollib/oftrees/oftree.nw.old), the mac-io node itself shouldn't
      have *any* interrupts properties. I wonder if that is what the error
      message is trying to say?
    - @markcaveayland That's the baffling part, here's the output of
      .properties after the boot fails: https://gist.github.com/cormac-
    - @cormacobrien2 That part is easy - for a PCI device such as macio, the
      values for the properties are extracted directly from the PCI
      configuration (as per the OF spec). First thing to check is whether
      removing the "interrupts" property will get things further - can you boot
      direct to the Forth prompt, remove the property manually with "delete-
      property" and then "boot" manually to see if it gets further or not?
    - @markcaveayland That appears to work -- got much further in the boot
      process than we have previously. Seems like I misinterpreted the error
      message, thinking the lack of interrupts was a problem, but it was
      actually that it had too many. Thanks!  Now on to the next error. I've
      updated the gist with the new log, which gives "Stopping at end of FCODE,
      due to fatal error (see above)." The only thing I can "see above" at the
      moment is on line 6516, with a "possible argument error". Obviously
      there's a lot more to look through, so I'll keep searching.
    - @cormacobrien2 Excellent! I wonder if the "Fatal Error" message is a
      final error check before execing the kernel, i.e. if the error flag has
      been set before jumping into the kernel then fail with the error first
      rather than carrying on?  Given that the remaining fatal error for -M
      mac99 is about being unable to find the /rtas node, I would suggest
      trying to fake one up and see if that helps. It is particularly telling
      that most of the /rtas words appear to be "made up" if you look at
      http://josejx.net/mol/mol-stable/mollib/oftrees/oftree.nw.old for
    - @cormacobrien2 Also I noticed a subtle issue at line 474 of your gist
      which may be relevant here - if not yet then very soon :)
    - @markcaveayland It looks like adding the device statically doesn't agree
      with instantiate-rtas (implemented in C as
      arch/ppc/qemu/methods.c:rtas_instantiate). rtas_instantiate doesn't
      appear to actually affect the device tree, but it looks to be reserving a
      page and copying to it from of_rtas_start. Is there any way to force a
      device's position in memory?
    - @cormac_obrien  Hmmm rtas is part of CHRP rather than Open Firmware so
      this sounds like a question for @agraf. Alex, any ideas?
    - RTAS are the "Runtime Services". Some code allocated in memory that an OS
      can jump to to do random firmware operations. It's very similar to BIOS
      or EFI Runtime Services.  The device tree part just tells the OS which
      address to call when it wants to do an RTAS call.
    - Setting the CONFIG_RTAS flag would probably have been a good idea
      *facepalm*, although it did still require the fake properties.
      @markcaveayland How do I go about setting that flag for build? I'm
      defining it in the source file and it works but I assume there's an XSL
      file I should be modifying somewhere, I just don't know where.  And the
      issue you mentioned is indeed relevant, but seems trivial enough. (famous
      last words...)
    - @cormac_obrien That's easy - just enable it in
      config/examples/ppc_config.xml. But note that the config XML files are
      only read by the switch-arch script so you'll need to remove all existing
      obj-* target directories, re-run config/scripts/switch-arch to regenerate
      them from the updated XML, and finally make once again to generate the
      new binaries.
    - Got it. A couple of cool developments, one being the attached AAPL,debug
      printout (see the last bit) and the other being this:  "Off to MacOS.
      The next (and last) call into OpenFirmware is quiesce()."  Of course, it
      hangs here, but it's still pretty cool to see. I've updated the log at
      https://gist.github.com/cormac-obrien/f7b1f0f600dd578fb7a5 again with the
      new execution.
    - @cormac_obrien Take a look at ob_pci_add_properties() in drivers/pci.c to
      see how the interrupts are set up. As for why the boot hangs, I can think
      of 2 reasons:  1) Are there any missing stack parameters to be returned
      by "quiesce"? The last line reads ">> of_client_interface return:" with
      no return value, so maybe something is amiss here?  2) Check out the very
      last line of your screenshot above ;)
    - @markcaveayland 2) is definitely not it, I cleared that bit as soon as I
      saw it. Not sure if you've looked at the comments in quiesce(), but
      they're less than reassuring :D I'll take a look and see if there could
      be something missing.
    - @cormac_obrien Cool. From memory I believe that the CIF call wrapper in
      client.fs "consumes" an extra stack parameter from the underlying word in
      order to indicate success or failure, before passing the remaining stack
      args back to the client. Check out other CIF words and their stack
      diagrams whilst stepping through the debugger to see what needs to be
      done here.
    - Since I've successfully set the "AAPL,debug" property, I'm going to move
      this card to "Done" and open a new one regarding the quiesce() call.
  - Patch: Adler-32 functionality
  - Send out intro email

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