[OpenBIOS] Help with libopenbios/ofmem_common.c line 175 "insert in the freelist"

[Kenneth Salerno]

Hi,

I finally got around to running QEMU in gdb to debug the AIX V6.1 boot hang and was able to get past where I got stuck previously:

-------------------------------------------------------------------------------
                                 Welcome to AIX.
                       boot image timestamp: 00:39 35/2D
NULL ihandle                 The current time and date: 00:00:00 228784/00/0008
        processor count: 1;  memory size: 1024MB;  kernel size: 2293829
                    boot device: cd:\ppc\chrp\bootfile.exe
Validation failed: the "/rtas" device node does not exist.
EXIT


It used to hang after "boot device: cd:\ppc\chrp\bootfile.exe" with OpenBIOS stuck at line 175 of libopenbios/ofmem_common.c:

  for( pp=&ofmem->mfree; *pp && (**pp).size < d->size ; pp = &(**pp).next ) {
  }


I made the following hack to get it to progress to the RTAS validation:

--- ofmem_common.c.ORIG 2011-08-08 17:04:25.375000000 -0400
+++ ofmem_common.c      2011-08-08 17:04:45.875000000 -0400
@@ -172,8 +172,9 @@
        d->next = ofmem->mfree;

        /* insert in the (sorted) freelist */
-       for( pp=&ofmem->mfree; *pp && (**pp).size < d->size ; pp = &(**pp).next
) {
-       }
+/*     for( pp=&ofmem->mfree; *pp && (**pp).size < d->size ; pp = &(**pp).next
) {
+       } */
+       pp=&ofmem->mfree;

        d->next = *pp;
        *pp = d;


Before I made the above change, the following is what I saw in gdb and qemu console:

  (qemu) info cpus
  * CPU #0: nip=0x00000000fff91a84 thread_id=6828

  (gdb)
  0x00000000fff91a84 in ofmem_free (ptr=0x3fca1774)
      at ../libopenbios/ofmem_common.c:175
  175   for( pp=&ofmem->mfree; *pp && (**pp).size < d->size ; pp = &(**pp).next ) {

  (gdb) print /x pp
  $1 = 0x3fc9e0ac

The value 0x3fc9e0ac can be found in register GPR08:

  (qemu) info registers
  NIP 00000000fff91a84   LR 00000000fff91a58 CTR 00000000fff93784 XER 000000002000
0000
  MSR 0000000000003032 HID0 0000000060000000  HF 0000000000002000 idx 1
  TB 00000001 7638146663 DECR 951787926
  GPR00 000000003fca1764 000000003fdf69e0 00000000fffc68e8 000000003fc9e0ac
  GPR04 00000000fffc0088 000000003fc5bc68 00000000fffc0860 0000000000044200
  GPR08 0000000000000002 000000003fc9e0ac 0000000000000024 0000000000000810
  GPR12 00000000000088ac 0000000000000000 00000000fffb6703 00000000fffb7b65
  GPR16 00000000fffb8331 00000000fffb6706 0000000004000000 00000000fffbf6b8
  GPR20 00000000fffbf634 00000000fffc68e8 00000000fffbf634 00000000fffb650a
  GPR24 00000000fffb64f8 00000000fffb6478 00000000fffb6500 00000000fffb6505
  GPR28 00000000fffb707e 0000000000000027 0000000000000027 000000003fca1774
  CR 48000084  [ G  L  -  -  -  -  L  G  ]             RES ffffffffffffffff
  FPR00 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR04 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR08 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR12 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR16 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR20 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR24 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPR28 0000000000000000 0000000000000000 0000000000000000 0000000000000000
  FPSCR 00000000
  SRR0 00000000fffaa590  SRR1 0000000000003032    PVR 00000000003c0301 VRSAVE 000
  0000000000000
  SPRG0 000000003fe00000 SPRG1 000000003fdf6630  SPRG2 0000000000000000  SPRG3 000
  0000000000000
  SPRG4 0000000000000000 SPRG5 0000000000000000  SPRG6 0000000000000000  SPRG7 000
  0000000000000
  SDR1 000000003fe00000
  

Here is my QEMU command:
  
   ./testing/qemu/ppc64-softmmu/qemu-system-ppc64 \
           -L ./testing/qemu/pc-bios \
           -m 1024 \
           -bios ./testing/openbios-devel/obj-ppc64/openbios-qemu.elf
           -drive file=images/aix.img,index=0,media=disk,cache=writeback
           -cdrom images/ibmaix.iso \
           -boot d \
           -nographic \
           -rtc base=localtime,clock=host \
           -uuid 17202d0a-45f8-4159-a8e1-78b866f50aa7 \
           -serial tcp::9979,server,nowait \
           -monitor tcp::9980,server,nowait \
           -gdb tcp::1234

  powerpc64-unknown-linux-gnu-gdb testing/openbios-devel/obj-ppc64/openbios-qemu.elf-nostrip

I don't really know what I'm doing so any help explaining this function in ofmem_common.c would be appreciated.

Thank you,
Ken