[Qemu-devel] [Bug 1527322] [NEW] undefined behavior issues

[Octoploid]

Public bug reported:

Building qemu-2.5.0 with -fsanitize=undefined shows, e.g.:

address@hidden linux % qemu-system-x86_64 -s -enable-kvm -net 
nic,vlan=0,model=virtio -net user -fsdev 
local,security_model=none,id=root,path=/ -device virtio-9p-pci,id=root,fsdev
=root,mount_tag=/dev/root -m 512 -smp 2 -kernel 
/usr/src/linux/arch/x86/boot/bzImage -nographic -append "init=/bin/zsh 
root=/dev/root console=ttyS0 kgdboc=ttyS0 rootflags=rw,
trans=virtio rootfstype=9p ip=dhcp earlyprintk=ttyS0"
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/exec.c:307:5: runtime 
error: variable length array bound evaluates to non-positive value 0
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/hw/i386/kvm/apic.c:37:47:
 runtime error: left shift of 15 by 28 places cannot be represented in type 
'int'
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:85:21:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:101:5:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:102:8:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
...
ALSA device list:
  No soundcards found.
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/thread-pool.c:246:5: 
runtime error: member access within null pointer of type 'struct ThreadPool'
[1]    9295 segmentation fault  qemu-system-x86_64 -s -enable-kvm -net 
nic,vlan=0,model=virtio -net user  

As you can see it segfaults when build with upcoming gcc-6, that is more 
aggressive when it comes to undefined behavior.
The compiler just assumes that "this" can never be NULL and optimizes 
accordingly.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1527322

Title:
  undefined behavior issues

Status in QEMU:
  New

Bug description:
  Building qemu-2.5.0 with -fsanitize=undefined shows, e.g.:

  address@hidden linux % qemu-system-x86_64 -s -enable-kvm -net 
nic,vlan=0,model=virtio -net user -fsdev 
local,security_model=none,id=root,path=/ -device virtio-9p-pci,id=root,fsdev
  =root,mount_tag=/dev/root -m 512 -smp 2 -kernel 
/usr/src/linux/arch/x86/boot/bzImage -nographic -append "init=/bin/zsh 
root=/dev/root console=ttyS0 kgdboc=ttyS0 rootflags=rw,
  trans=virtio rootfstype=9p ip=dhcp earlyprintk=ttyS0"
  /var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/exec.c:307:5: 
runtime error: variable length array bound evaluates to non-positive value 0
  
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/hw/i386/kvm/apic.c:37:47:
 runtime error: left shift of 15 by 28 places cannot be represented in type 
'int'
  
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:85:21:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
  
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:101:5:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
  
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/include/qemu/rcu.h:102:8:
 runtime error: member access within null pointer of type 'struct 
rcu_reader_data'
  ...
  ALSA device list:
    No soundcards found.
  
/var/tmp/portage/app-emulation/qemu-2.5.0/work/qemu-2.5.0/thread-pool.c:246:5: 
runtime error: member access within null pointer of type 'struct ThreadPool'
  [1]    9295 segmentation fault  qemu-system-x86_64 -s -enable-kvm -net 
nic,vlan=0,model=virtio -net user  

  As you can see it segfaults when build with upcoming gcc-6, that is more 
aggressive when it comes to undefined behavior.
  The compiler just assumes that "this" can never be NULL and optimizes 
accordingly.

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