[Qemu-devel] [Bug 1817525] Re: qemu fails to compile on gcc 9 "block/nvme.c:209:22: error: taking address of packed member of 'struct <anonymous>' may result in an unaligned pointer value [-Werror=address-of-packed-member]"

[Thomas Huth]

** Changed in: qemu
       Status: Fix Committed => Fix Released

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Title:
  qemu fails to compile on gcc 9 "block/nvme.c:209:22: error: taking
  address of packed member of 'struct <anonymous>' may result in an
  unaligned pointer value [-Werror=address-of-packed-member]"

Status in QEMU:
  Fix Released

Bug description:
  Issue:
  Qemu compilation fails with below error on ppc64le host with gcc 9, 
repo(https://github.com/dgibson/qemu.git), branch(ppc-for-4.0), Commit 
(0483e90393bac8546a1fbc95ab912a1e78e92b00)

   CHK version_gen.h
    CC      block/nvme.o
  block/nvme.c: In function ‘nvme_create_queue_pair’:
  block/nvme.c:209:22: error: taking address of packed member of ‘struct 
<anonymous>’ may result in an unaligned pointer value 
[-Werror=address-of-packed-member]
    209 |     q->sq.doorbell = &s->regs->doorbells[idx * 2 * s->doorbell_scale];
        |                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  block/nvme.c:216:22: error: taking address of packed member of ‘struct 
<anonymous>’ may result in an unaligned pointer value 
[-Werror=address-of-packed-member]
    216 |     q->cq.doorbell = &s->regs->doorbells[idx * 2 * s->doorbell_scale 
+ 1];
        |                      
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors
  make: *** [/usr/share/avocado-plugins-vt/build/qemu/rules.mak:69: 
block/nvme.o] Error 1

  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  $git commit:
  commit 0483e90393bac8546a1fbc95ab912a1e78e92b00 (HEAD -> ppc-for-4.0)
  Author: Thomas Huth <address@hidden>
  Date:   Thu Feb 21 12:24:48 2019 +0100

      hw/ppc: Use object_initialize_child for correct reference counting

      Both functions, object_initialize() and object_property_add_child() 
increase
      the reference counter of the new object, so one of the references has to 
be
      dropped afterwards to get the reference counting right. Otherwise the 
child
      object will not be properly cleaned up when the parent gets destroyed.
      Thus let's use now object_initialize_child() instead to get the reference
      counting here right.

      Suggested-by: Eduardo Habkost <address@hidden>
      Signed-off-by: Thomas Huth <address@hidden>
      Message-Id: <address@hidden>
      Reviewed-by: Cédric Le Goater <address@hidden>
      Signed-off-by: David Gibson <address@hidden>
  ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

  Note: Same commit on a different ppc64le host with gcc(8.1.1 20180712)
  compile without any issue.

  Host Env:

  Power8

  #lscpu
  Architecture:         ppc64le
  Byte Order:           Little Endian
  CPU(s):               160
  On-line CPU(s) list:  
0,8,16,24,32,40,48,56,64,72,80,88,96,104,112,120,128,136,144,152
  Off-line CPU(s) list: 
1-7,9-15,17-23,25-31,33-39,41-47,49-55,57-63,65-71,73-79,81-87,89-95,97-103,105-111,113-119,121-127,129-135,137-143,145-151,153-159
  Thread(s) per core:   1
  Core(s) per socket:   5
  Socket(s):            4
  NUMA node(s):         4
  Model:                2.1 (pvr 004b 0201)
  Model name:           POWER8E (raw), altivec supported
  CPU max MHz:          3690.0000
  CPU min MHz:          2061.0000
  L1d cache:            64K
  L1i cache:            32K
  L2 cache:             512K
  L3 cache:             8192K
  NUMA node0 CPU(s):    0,8,16,24,32
  NUMA node1 CPU(s):    40,48,56,64,72
  NUMA node16 CPU(s):   80,88,96,104,112
  NUMA node17 CPU(s):   120,128,136,144,152

  # gcc --version
  gcc (GCC) 9.0.1 20190209 (Red Hat 9.0.1-0.4)
  Copyright (C) 2019 Free Software Foundation, Inc.
  This is free software; see the source for copying conditions.  There is NO
  warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

  # uname -r
  5.0.0-rc7-ge50585e89

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