segfault when building the xworkspace-nodes from desktop-labels #1444
Description
I sometimes run into a segfault during my work on #882 .
Expected behavior:
I expect no segfault :-)
Actual behavior:
When running the bar under gdb until the segfault, I get the following backtrace:
#0 std::__shared_ptr<polybar::v3_2_0_52_g1550152_git::drawtypes::label, (__gnu_cxx::_Lock_policy)2>::get (this=0x10)
at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/bits/shared_ptr_base.h:1060
#1 <function called from gdb>
#2 std::__shared_ptr<polybar::v3_2_0_52_g1550152_git::drawtypes::label, (__gnu_cxx::_Lock_policy)2>::get (this=0x10)
at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/bits/shared_ptr_base.h:1060
Python Exception <class 'gdb.error'> There is no member named _M_dataplus.:
#3 0x00000000009114a7 in polybar::v3_2_0_52_g1550152_git::modules::xworkspaces_module::build (this=0xcf5760, builder=0xcf5bf0, tag=)
at /home/mviehweger/Code/opensource/polybar/src/modules/xworkspaces.cpp:310
#4 0x000000000091a1f5 in polybar::v3_2_0_52_g1550152_git::modules::module<polybar::v3_2_0_52_g1550152_git::modules::xworkspaces_module>::get_output[abi:cxx11]() (this=0xcf5760) at /home/mviehweger/Code/opensource/polybar/include/modules/meta/base.inl:160
#5 0x0000000000910e95 in polybar::v3_2_0_52_g1550152_git::modules::xworkspaces_module::get_output[abi:cxx11]() (this=0xcf5760)
at /home/mviehweger/Code/opensource/polybar/src/modules/xworkspaces.cpp:280
#6 0x0000000000919a0d in polybar::v3_2_0_52_g1550152_git::modules::module<polybar::v3_2_0_52_g1550152_git::modules::xworkspaces_module>::contents[abi:cxx11]() (this=0xcf5760) at /home/mviehweger/Code/opensource/polybar/include/modules/meta/base.inl:82
#7 0x00000000007bf711 in polybar::v3_2_0_52_g1550152_git::controller::process_update (this=0xcf4b70, force=false)
at /home/mviehweger/Code/opensource/polybar/src/components/controller.cpp:481
#8 0x00000000007bd22b in polybar::v3_2_0_52_g1550152_git::controller::process_eventqueue (this=0xcf4b70)
at /home/mviehweger/Code/opensource/polybar/src/components/controller.cpp:394
#9 0x00000000007d36c9 in std::_Mem_fn_base<void (polybar::v3_2_0_52_g1550152_git::controller::*)(), true>::operator()<, void>(polybar::v3_2_0_52_g1550152_git::controller*) const (this=0xd30ca0, __object=0xcf4b70) at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/functional:600
#10 0x00000000007d3632 in std::_Bind_simple<std::_Mem_fn<void (polybar::v3_2_0_52_g1550152_git::controller::*)()> (polybar::v3_2_0_52_g1550152_git::controller*)>::_M_invoke<0ul>(std::_Index_tuple<0ul>) (this=0xd30c98) at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/functional:1530
#11 0x00000000007d35e5 in std::_Bind_simple<std::_Mem_fn<void (polybar::v3_2_0_52_g1550152_git::controller::*)()> (polybar::v3_2_0_52_g1550152_git::controller*)>::operator()() (this=0xd30c98) at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/functional:1520
#12 0x00000000007d33a9 in std::thread::_Impl<std::_Bind_simple<std::_Mem_fn<void (polybar::v3_2_0_52_g1550152_git::controller::*)()> (polybar::v3_2_0_52_g1550152_git::controller*)> >::_M_run() (this=0xd30c80) at /usr/bin/../lib/gcc/x86_64-linux-gnu/5.4.0/../../../../include/c++/5.4.0/thread:115
#13 0x00007ffff54b5c80 in ?? () from /usr/lib/x86_64-linux-gnu/libstdc++.so.6
#14 0x00007ffff4cc86ba in start_thread (arg=0x7fffe17fa700) at pthread_create.c:333
#15 0x00007ffff49fe41d in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
Environment:
- WM: xmonad
- Output of
polybar -vvv:
polybar 3.2.0-52-g1550152-git
Features: +alsa +curl -i3 +mpd +network(wireless-tools) +pulseaudio +xkeyboard
X extensions: +randr (-monitors) -render -damage -sync -composite +xkb +xrm -xcursor
Build type: Debug
Compiler: /usr/bin/clang++
Compiler flags: -Wall -Wextra -Werror -O2 -pedantic -pedantic-errors -Wno-error=parentheses-equality -Wno-zero-length-array
Linker flags:
The master of polybar that I am building on top of is 2fba443.
Attempted debugging
PR #882 does not change the source-code from which the segfault originates, but it shifts its location a few lines down. See https://github.com/jaagr/polybar/pull/882/files#diff-e89fe726ad41f4ae273dacfca026a7ddR310 for the code mentioned here.
From the above backtrace, I poked around a little to know more. In order to establish the context in which this on segfaults, I did the following:
(gdb) f 3
Python Exception <class 'gdb.error'> There is no member named _M_dataplus.:
#3 0x00000000009114a7 in polybar::v3_2_0_52_g1550152_git::modules::xworkspaces_module::build (this=0xcf5760, builder=0xcf5bf0, tag=)
at /home/mviehweger/Code/opensource/polybar/src/modules/xworkspaces.cpp:310
310 if (desktop->label.get()) {
(gdb) p m_index
$2 = 0
(gdb) p m_viewports
$3 = std::vector of length 1, capacity 1 = {std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::viewport> containing 0xcef500}
(gdb) p m_viewports[0]->desktops
$4 = std::vector of length 9, capacity 16 = {std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd69690,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd03380,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd41e50,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd37830,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd3ac80,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd03a30,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd3ad70,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd38460,
std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0xd4b2b0}
(gdb) p desktop
$5 = std::unique_ptr<polybar::v3_2_0_52_g1550152_git::modules::desktop> containing 0x0
Related Problems
This time, the segfault originates from desktop->label.get(), other times, it manages to get a few lines further until desktop->label is called/passed to the builder.
I assume by now, that xmonad changes the desktop-properties and that this somehow invalidates/corrupts the data-structure. My proposed solution is to add another check against invalid desktop-pointers.
Keep in mind, I have little knowledge about X11-properties, C++(-datastructures) and the interaction between the moving parts here.