[Bug 1776096] Re: qemu 2.12.0 qemu-system-ppc illegal instruction on ppc64le, crashes emulator

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/1776096

Title:
  qemu 2.12.0 qemu-system-ppc illegal instruction on ppc64le, crashes
  emulator

Status in QEMU:
  Expired

Bug description:
  % uname -a
  Linux tim.floodgap.com 4.16.14-300.fc28.ppc64le #1 SMP Tue Jun 5 15:59:48 UTC 
2018 ppc64le ppc64le ppc64le GNU/Linux

  STR:
  Start QEMU and boot Mac OS X 10.4.11.
  Download the current version of TenFourFox (I used G3 so that AltiVec was not 
a confounder).
  Try to start TenFourFox in safe mode (hold down Option as you double-click 
while the icon bounces in the Dock).

  Expected:
  TenFourFox starts.

  Actual:
  The entire emulator exits with an illegal instruction error.

  Trace of session (including some disassembly so you can see where TCG
  went wrong):

  tim:/home/spectre/src/qemu-2.12.0/ppc-softmmu/% gdb --args ./qemu-
  system-ppc -M mac99,accel=tcg -m 2048 -prom-env boot-args=-v -boot c
  -drive file=tigerhd.img,format=raw,cache=none -netdev user,id=mynet0
  -device usb-net,netdev=mynet0 -usb -device usb-tablet

  GNU gdb (GDB) Fedora 8.1-15.fc28
  [...]
  Reading symbols from ./qemu-system-ppc...done.
  (gdb) run
  [...]

  Thread 6 "qemu-system-ppc" received signal SIGSEGV, Segmentation fault.
  [Switching to Thread 0x7ffff242ea30 (LWP 7017)]
  0xfffffffffffffffc in ?? ()
  #0  0xfffffffffffffffc in  ()
  #1  0x00007fffd4edec00 in code_gen_buffer ()
  #2  0x00000000100c9e20 in cpu_tb_exec (itb=<optimized out>, cpu=<optimized 
out>) at /home/spectre/src/qemu-2.12.0/accel/tcg/cpu-exec.c:169
  #3  0x00000000100c9e20 in cpu_loop_exec_tb (tb_exit=<synthetic pointer>, 
last_tb=<synthetic pointer>, tb=<optimized out>, cpu=<optimized out>)
      at /home/spectre/src/qemu-2.12.0/accel/tcg/cpu-exec.c:626
  #4  0x00000000100c9e20 in cpu_exec (cpu=<optimized out>)
      at /home/spectre/src/qemu-2.12.0/accel/tcg/cpu-exec.c:734
  #5  0x000000001007decc in tcg_cpu_exec (cpu=0x11774e10)
      at /home/spectre/src/qemu-2.12.0/cpus.c:1362
  (gdb) disas 0x00007fffd4edebf0, 0x00007fffd4edec10
  Dump of assembler code from 0x7fffd4edebf0 to 0x7fffd4edec10:
     0x00007fffd4edebf0 <code_gen_buffer+284027700>:    addi    r0,r4,3
     0x00007fffd4edebf4 <code_gen_buffer+284027704>:    rlwinm  r0,r0,0,0,19
     0x00007fffd4edebf8 <code_gen_buffer+284027708>:    cmplw   cr7,r0,r12
     0x00007fffd4edebfc <code_gen_buffer+284027712>:    bnel    
cr7,0x7fffd4ed8b64 <code_gen_buffer+284002984>
     0x00007fffd4edec00 <code_gen_buffer+284027716>:    lwbrx   r14,r3,r4
     0x00007fffd4edec04 <code_gen_buffer+284027720>:    stw     r14,40(r27)
     0x00007fffd4edec08 <code_gen_buffer+284027724>:    clrldi  r4,r14,32
     0x00007fffd4edec0c <code_gen_buffer+284027728>:    rlwinm  r3,r4,25,19,26
  End of assembler dump.
  (gdb) disas 0x7fffd4ed8b60, 0x7fffd4ed8b70
  Dump of assembler code from 0x7fffd4ed8b60 to 0x7fffd4ed8b70:
     0x00007fffd4ed8b60 <code_gen_buffer+284002980>:    bctrl
     0x00007fffd4ed8b64 <code_gen_buffer+284002984>:    mtctr   r3
     0x00007fffd4ed8b68 <code_gen_buffer+284002988>:    mr      r31,r3
     0x00007fffd4ed8b6c <code_gen_buffer+284002992>:    li      r3,0
  End of assembler dump.
  (gdb) i reg ctr
  ctr            0xffffffffffffffff     18446744073709551615

  It appears that the branch at 0x00007fffd4edebfc caused a jump back (a
  return?) through CTR, but CTR has -1 in it, hence setting PC to
  0xfffffffffffffffc. I am not sure how to debug this further.

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