Frequently asked questions¶

meta-microblx yocto layer: luajit build fails¶

luajit fails with the following message:

arm-poky-linux-gnueabi-gcc  -mfpu=neon -mfloat-abi=hard -mcpu=cortex-a8 -fstack-protector-strong  -D_FORTIFY_SOURCE=2 -Wformat -Wformat-security -Werror=format-security --sysroot=/build/bbblack-zeus/build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/luajit/2.0.5+gitAUTOINC+02b521981a-r0/recipe-sysroot -fPIC   -Wall   -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -U_FORTIFY_SOURCE  -DLUA_ROOT=\"/usr\" -DLUA_MULTILIB=\"lib\" -fno-stack-protector  -O2 -pipe -g -feliminate-unused-debug-types -fmacro-prefix-map=/build/bbblack-zeus/build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/luajit/2.0.5+gitAUTOINC+02b521981a-r0=/usr/src/debug/luajit/2.0.5+gitAUTOINC+02b521981a-r0                      -fdebug-prefix-map=/build/bbblack-zeus/build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/luajit/2.0.5+gitAUTOINC+02b521981a-r0=/usr/src/debug/luajit/2.0.5+gitAUTOINC+02b521981a-r0                      -fdebug-prefix-map=/build/bbblack-zeus/build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/luajit/2.0.5+gitAUTOINC+02b521981a-r0/recipe-sysroot=                      -fdebug-prefix-map=/build/bbblack-zeus/build/tmp/work/cortexa8hf-neon-poky-linux-gnueabi/luajit/2.0.5+gitAUTOINC+02b521981a-r0/recipe-sysroot-native=  -c -o lj_obj_dyn.o lj_obj.c
In file included from /usr/include/bits/errno.h:26,
                 from /usr/include/errno.h:28,
                 from host/buildvm.h:13,
                 from host/buildvm_fold.c:6:
/usr/include/linux/errno.h:1:10: fatal error: asm/errno.h: No such file or directory
    1 | #include <asm/errno.h>
      |          ^~~~~~~~~~~~~
compilation terminated.

This solution is to install gcc-multilib on the build host.

fix “error object is not a string”¶

Note that this has been fixed in commit be63f6408bd4d.

This is most of the time happens when the strict module being loaded (also indirectly, e.g. via ubx.lua) in a luablock. It is caused by the C code looking up a non-existing global hook function. Solution: either define all hooks or disable the strict module for the luablock.

`blockXY`.so or `liblfds611.so.0`: cannot open shared object file: No such file or directory¶

There seems to be a bug in some versions of libtool which leads to the ld cache not being updated. You can manually fix this by running

$ sudo ldconfig

Often this means that the location of the shared object file is not in the library search path. If you installed to a non-standard location, try adding it to LD_LIBRARY_PATH, e.g.

$ export LD_LIBRARY_PATH=/usr/local/lib/

It would be better to install stuff in a standard location such as /usr/local/.

Real-time priorities¶

To run with realtime priorities, give the luajit binary cap_sys_nice capabilities, e.g:

$ sudo setcap cap_sys_nice+ep `which luajit`

Note that this will grant these capabilities to luajit binary in PATH. If you don’t want to do this system-wide, then specify a different version!

My script immedately crashes/finishes¶

This can have several reasons:

You forgot the -i option to luajit: in that case the script is executed and once completed will immedately exit. The system will be shut down / cleaned up rather rougly.
You ran the wrong Lua executable (e.g. a standard Lua instead of luajit).

If none of this works, see the following topic.

Debugging segfaults¶

One of the best ways to debug crashes is using gdb and the core dump file:

# enable core dumps
$ ulimit -c unlimited
$ gdb luajit
...
(gdb) core-file core
...
(gdb) bt

Sometimes, running gdb directly on the processes produces better results than post-mortem coredumps. For example, to run the pid example with gdb attached:

$ cd /usr/local/share/ubx/examples/usc/pid
$ gdb luajit --args luajit `which ubx-launch` -c pid_test.usc,ptrig_nrt.usc
GNU gdb (Debian 9.1-2) 9.1
...
Reading symbols from luajit...
(No debugging symbols found in luajit)
(gdb) run
Starting program: /usr/bin/luajit /usr/local/bin/ubx-launch -c pid_test.usc,ptrig_nrt.usc
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
merging ptrig_nrt.usc into pid_test.usc
core_prefix: /usr/local
prefixes:    /usr, /usr/local
[New Thread 0x7ffff7871700 (LWP 2831757)]
...