coredump: implement logging of external backtraces with --backtrace

coredump: implement logging of external backtraces with --backtrace

This is useful for example for Python progams. By installing a python
sys.execepthook we can store the backtrace in the journal. We gather the
backtrace in the python process, and call systemd-coredump to attach additional
fields (COREDUMP_COMM, COREDUMP_EXE, COREDUMP_UNIT, COREDUMP_USER_UNIT,
COREDUMP_OWNER_UID, COREDUMP_SLICE, COREDUMP_CMDLINE, COREDUMP_CGROUP,
COREDUMP_OPEN_FDS, COREDUMP_PROC_STATUS, COREDUMP_PROC_MAPS,
COREDUMP_PROC_LIMITS, COREDUMP_PROC_MOUNTINFO, COREDUMP_CWD, COREDUMP_ROOT,
COREDUMP_ENVIRON, COREDUMP_CONTAINER_CMDLINE). This could also be done in the
python process, but doing this in systemd-coredump saves quite a bit of
duplicate work and unifies the handling of various tricky fields like
COREDUMP_CONTAINER_CMDLINE in one place.

(Of course this applies to any other language which does not dump cores
but wants to log a traceback, e.g. ruby.)

journal entry:
    _TRANSPORT=journal
    _UID=1002
    _GID=1002
    _CAP_EFFECTIVE=0
    _AUDIT_LOGINUID=1002
    _SYSTEMD_OWNER_UID=1002
    _SYSTEMD_SLICE=user-1002.slice
    _SYSTEMD_USER_SLICE=-.slice
    _SELINUX_CONTEXT=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
    _BOOT_ID=1531fd22ec84429e85ae888b12fadb91
    _MACHINE_ID=519a16632fbd4c71966ce9305b360c9c
    _HOSTNAME=laptop
    _AUDIT_SESSION=1
    _SYSTEMD_UNIT=user@1002.service
    _SYSTEMD_INVOCATION_ID=3c4238d790a44aca9576ecdb2c7576d3
    COREDUMP_UNIT=user@1002.service
    COREDUMP_USER_UNIT=gnome-terminal-server.service
    COREDUMP_UID=1002
    COREDUMP_GID=1002
    COREDUMP_OWNER_UID=1002
    COREDUMP_SLICE=user-1002.slice
    COREDUMP_CGROUP=/user.slice/user-1002.slice/user@1002.service/gnome-terminal-server.service
    COREDUMP_PROC_LIMITS=Limit                     Soft Limit           Hard Limit           Units
                         Max cpu time              unlimited            unlimited            seconds
                         Max file size             unlimited            unlimited            bytes
                         Max data size             unlimited            unlimited            bytes
                         Max stack size            8388608              unlimited            bytes
                         Max core file size        unlimited            unlimited            bytes
                         Max resident set          unlimited            unlimited            bytes
                         Max processes             15413                15413                processes
                         Max open files            4096                 4096                 files
                         Max locked memory         65536                65536                bytes
                         Max address space         unlimited            unlimited            bytes
                         Max file locks            unlimited            unlimited            locks
                         Max pending signals       15413                15413                signals
                         Max msgqueue size         819200               819200               bytes
                         Max nice priority         0                    0
                         Max realtime priority     0                    0
                         Max realtime timeout      unlimited            unlimited            us
    COREDUMP_PROC_CGROUP=1:name=systemd:/
                         0::/user.slice/user-1002.slice/user@1002.service/gnome-terminal-server.service
    COREDUMP_PROC_MOUNTINFO=17 39 0:17 / /sys rw,nosuid,nodev,noexec,relatime shared:6 - sysfs sysfs rw,seclabel
                            18 39 0:4 / /proc rw,nosuid,nodev,noexec,relatime shared:5 - proc proc rw
                            19 39 0:6 / /dev rw,nosuid shared:2 - devtmpfs devtmpfs rw,seclabel,size=1972980k,nr_inodes=493245,mode=755
                            20 17 0:18 / /sys/kernel/security rw,nosuid,nodev,noexec,relatime shared:7 - securityfs securityfs rw
                            21 19 0:19 / /dev/shm rw,nosuid,nodev shared:3 - tmpfs tmpfs rw,seclabel
                            22 19 0:20 / /dev/pts rw,nosuid,noexec,relatime shared:4 - devpts devpts rw,seclabel,gid=5,mode=620,ptmxmode=000
                            23 39 0:21 / /run rw,nosuid,nodev shared:12 - tmpfs tmpfs rw,seclabel,mode=755
                            24 17 0:22 / /sys/fs/cgroup rw,nosuid,nodev,noexec,relatime shared:8 - cgroup2 cgroup rw
                            25 17 0:23 / /sys/fs/pstore rw,nosuid,nodev,noexec,relatime shared:9 - pstore pstore rw,seclabel
                            36 17 0:24 / /sys/kernel/config rw,relatime shared:10 - configfs configfs rw
                            39 0 0:26 /root / rw,relatime shared:1 - btrfs /dev/mapper/fedora-root2 rw,seclabel,ssd,space_cache,subvolid=257,subvol=/root
                            26 17 0:16 / /sys/fs/selinux rw,relatime shared:11 - selinuxfs selinuxfs rw
                            27 19 0:15 / /dev/mqueue rw,relatime shared:13 - mqueue mqueue rw,seclabel
                            28 18 0:30 / /proc/sys/fs/binfmt_misc rw,relatime shared:14 - autofs systemd-1 rw,fd=35,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=13663
                            29 17 0:7 / /sys/kernel/debug rw,relatime shared:15 - debugfs debugfs rw,seclabel
                            30 19 0:31 / /dev/hugepages rw,relatime shared:16 - hugetlbfs hugetlbfs rw,seclabel
                            31 18 0:32 / /proc/fs/nfsd rw,relatime shared:17 - nfsd nfsd rw
                            32 28 0:33 / /proc/sys/fs/binfmt_misc rw,relatime shared:18 - binfmt_misc binfmt_misc rw
                            57 39 0:34 / /tmp rw,relatime shared:19 - tmpfs none rw,seclabel
                            61 57 0:35 / /tmp/test rw,relatime shared:20 - autofs systemd-1 rw,fd=48,pgrp=1,timeout=0,minproto=5,maxproto=5,direct,pipe_ino=18251
                            59 39 8:1 / /boot rw,relatime shared:21 - ext4 /dev/sda1 rw,seclabel,data=ordered
                            60 39 253:2 / /home rw,relatime shared:22 - ext4 /dev/mapper/fedora-home rw,seclabel,data=ordered
                            65 39 0:37 / /var/lib/nfs/rpc_pipefs rw,relatime shared:23 - rpc_pipefs sunrpc rw
                            136 23 0:39 / /run/user/1002 rw,nosuid,nodev,relatime shared:91 - tmpfs tmpfs rw,seclabel,size=397432k,mode=700,uid=1002,gid=1002
                            211 23 0:41 / /run/user/42 rw,nosuid,nodev,relatime shared:163 - tmpfs tmpfs rw,seclabel,size=397432k,mode=700,uid=42,gid=42
                            329 136 0:44 / /run/user/1002/gvfs rw,nosuid,nodev,relatime shared:277 - fuse.gvfsd-fuse gvfsd-fuse rw,user_id=1002,group_id=1002
                            287 61 253:3 / /tmp/test rw,relatime shared:236 - ext4 /dev/mapper/fedora-test rw,seclabel,data=ordered
                            217 23 0:42 / /run/user/1000 rw,nosuid,nodev,relatime shared:168 - tmpfs tmpfs rw,seclabel,size=397432k,mode=700,uid=1000,gid=1000
                            225 217 0:43 / /run/user/1000/gvfs rw,nosuid,nodev,relatime shared:175 - fuse.gvfsd-fuse gvfsd-fuse rw,user_id=1000,group_id=1000
    COREDUMP_ROOT=/
    PRIORITY=2
    CODE_FILE=src/coredump/coredump.c
    SYSLOG_IDENTIFIER=lt-systemd-coredump
    _COMM=lt-systemd-core
    _SYSTEMD_CGROUP=/user.slice/user-1002.slice/user@1002.service/gnome-terminal-server.service
    _SYSTEMD_USER_UNIT=gnome-terminal-server.service
    MESSAGE_ID=1f4e0a44a88649939aaea34fc6da8c95
    CODE_FUNC=process_traceback
    COREDUMP_COMM=python3
    COREDUMP_EXE=/usr/bin/python3.5
    COREDUMP_CMDLINE=python3 systemd_coredump_exception_handler.py
    COREDUMP_CWD=/home/zbyszek/src/systemd-coredump-python
    COREDUMP_RLIMIT=-1
    COREDUMP_OPEN_FDS=0:/dev/pts/1
                      pos:	0
                      flags:	0102002
                      mnt_id:	22

                      1:/dev/pts/1
                      pos:	0
                      flags:	0102002
                      mnt_id:	22

                      2:/dev/pts/1
                      pos:	0
                      flags:	0102002
                      mnt_id:	22
    CODE_LINE=1284
    COREDUMP_SIGNAL=ZeroDivisionError: division by zero
    COREDUMP_ENVIRON=LANG=en_US.utf8
                     DISPLAY=:0
                     ...
                     MANWIDTH=90
                     LC_MESSAGES=en_US.utf8
                     PYTHONPATH=.
                     _=/usr/bin/python3
    COREDUMP_PID=14498
    COREDUMP_PROC_STATUS=Name:	python3
                         Umask:	0002
                         State:	S (sleeping)
                         Tgid:	14498
                         Ngid:	0
                         Pid:	14498
                         PPid:	16245
                         TracerPid:	0
                         Uid:	1002	1002	1002	1002
                         Gid:	1002	1002	1002	1002
                         FDSize:	64
                         Groups:
                         NStgid:	14498
                         NSpid:	14498
                         NSpgid:	14498
                         NSsid:	16245
                         VmPeak:	   34840 kB
                         VmSize:	   34792 kB
                         VmLck:	       0 kB
                         VmPin:	       0 kB
                         VmHWM:	    9332 kB
                         VmRSS:	    9332 kB
                         RssAnon:	    4872 kB
                         RssFile:	    4460 kB
                         RssShmem:	       0 kB
                         VmData:	    5012 kB
                         VmStk:	     136 kB
                         VmExe:	       4 kB
                         VmLib:	    5452 kB
                         VmPTE:	      84 kB
                         VmPMD:	      12 kB
                         VmSwap:	       0 kB
                         HugetlbPages:	       0 kB
                         Threads:	1
                         SigQ:	0/15413
                         SigPnd:	0000000000000000
                         ShdPnd:	0000000000000000
                         SigBlk:	0000000000000000
                         SigIgn:	0000000001001000
                         SigCgt:	0000000180000002
                         CapInh:	0000000000000000
                         CapPrm:	0000000000000000
                         CapEff:	0000000000000000
                         CapBnd:	0000003fffffffff
                         CapAmb:	0000000000000000
                         Seccomp:	0
                         Cpus_allowed:	f
                         Cpus_allowed_list:	0-3
                         Mems_allowed:	00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000001
                         Mems_allowed_list:	0
                         voluntary_ctxt_switches:	2
                         nonvoluntary_ctxt_switches:	47
    COREDUMP_PROC_MAPS=55cb7b7fe000-55cb7b7ff000 r-xp 00000000 00:1a 5289186                    /usr/bin/python3.5
                       55cb7b9ff000-55cb7ba00000 r--p 00001000 00:1a 5289186                    /usr/bin/python3.5
                       55cb7ba00000-55cb7ba01000 rw-p 00002000 00:1a 5289186                    /usr/bin/python3.5
                       55cb7c007000-55cb7c189000 rw-p 00000000 00:00 0                          [heap]
                       7f4da2d51000-7f4da2d54000 r-xp 00000000 00:1a 5279150                    /usr/lib64/python3.5/lib-dynload/resource.cpython-35m-x86_64-linux-gnu.so
                       7f4da2d54000-7f4da2f53000 ---p 00003000 00:1a 5279150                    /usr/lib64/python3.5/lib-dynload/resource.cpython-35m-x86_64-linux-gnu.so
                       7f4da2f53000-7f4da2f54000 r--p 00002000 00:1a 5279150                    /usr/lib64/python3.5/lib-dynload/resource.cpython-35m-x86_64-linux-gnu.so
                       7f4da2f54000-7f4da2f55000 rw-p 00003000 00:1a 5279150                    /usr/lib64/python3.5/lib-dynload/resource.cpython-35m-x86_64-linux-gnu.so
                       7f4da2f55000-7f4da2f5d000 r-xp 00000000 00:1a 5279143                    /usr/lib64/python3.5/lib-dynload/math.cpython-35m-x86_64-linux-gnu.so
                       7f4da2f5d000-7f4da315c000 ---p 00008000 00:1a 5279143                    /usr/lib64/python3.5/lib-dynload/math.cpython-35m-x86_64-linux-gnu.so
                       7f4da315c000-7f4da315d000 r--p 00007000 00:1a 5279143                    /usr/lib64/python3.5/lib-dynload/math.cpython-35m-x86_64-linux-gnu.so
                       7f4da315d000-7f4da315f000 rw-p 00008000 00:1a 5279143                    /usr/lib64/python3.5/lib-dynload/math.cpython-35m-x86_64-linux-gnu.so
                       7f4da315f000-7f4da319f000 rw-p 00000000 00:00 0
                       7f4da319f000-7f4da31a4000 r-xp 00000000 00:1a 5279151                    /usr/lib64/python3.5/lib-dynload/select.cpython-35m-x86_64-linux-gnu.so
                       7f4da31a4000-7f4da33a3000 ---p 00005000 00:1a 5279151                    /usr/lib64/python3.5/lib-dynload/select.cpython-35m-x86_64-linux-gnu.so
                       7f4da33a3000-7f4da33a4000 r--p 00004000 00:1a 5279151                    /usr/lib64/python3.5/lib-dynload/select.cpython-35m-x86_64-linux-gnu.so
                       7f4da33a4000-7f4da33a6000 rw-p 00005000 00:1a 5279151                    /usr/lib64/python3.5/lib-dynload/select.cpython-35m-x86_64-linux-gnu.so
                       7f4da33a6000-7f4da33a9000 r-xp 00000000 00:1a 5279130                    /usr/lib64/python3.5/lib-dynload/_posixsubprocess.cpython-35m-x86_64-linux-gnu.so
                       7f4da33a9000-7f4da35a8000 ---p 00003000 00:1a 5279130                    /usr/lib64/python3.5/lib-dynload/_posixsubprocess.cpython-35m-x86_64-linux-gnu.so
                       7f4da35a8000-7f4da35a9000 r--p 00002000 00:1a 5279130                    /usr/lib64/python3.5/lib-dynload/_posixsubprocess.cpython-35m-x86_64-linux-gnu.so
                       7f4da35a9000-7f4da35aa000 rw-p 00003000 00:1a 5279130                    /usr/lib64/python3.5/lib-dynload/_posixsubprocess.cpython-35m-x86_64-linux-gnu.so
                       7f4da35aa000-7f4da362a000 rw-p 00000000 00:00 0
                       7f4da362a000-7f4da362c000 r-xp 00000000 00:1a 5279122                    /usr/lib64/python3.5/lib-dynload/_heapq.cpython-35m-x86_64-linux-gnu.so
                       7f4da362c000-7f4da382b000 ---p 00002000 00:1a 5279122                    /usr/lib64/python3.5/lib-dynload/_heapq.cpython-35m-x86_64-linux-gnu.so
                       7f4da382b000-7f4da382c000 r--p 00001000 00:1a 5279122                    /usr/lib64/python3.5/lib-dynload/_heapq.cpython-35m-x86_64-linux-gnu.so
                       7f4da382c000-7f4da382e000 rw-p 00002000 00:1a 5279122                    /usr/lib64/python3.5/lib-dynload/_heapq.cpython-35m-x86_64-linux-gnu.so
                       7f4da382e000-7f4da39ee000 rw-p 00000000 00:00 0
                       7f4da39ee000-7f4da3bab000 r-xp 00000000 00:1a 4844904                    /usr/lib64/libc-2.24.so
                       7f4da3bab000-7f4da3daa000 ---p 001bd000 00:1a 4844904                    /usr/lib64/libc-2.24.so
                       7f4da3daa000-7f4da3dae000 r--p 001bc000 00:1a 4844904                    /usr/lib64/libc-2.24.so
                       7f4da3dae000-7f4da3db0000 rw-p 001c0000 00:1a 4844904                    /usr/lib64/libc-2.24.so
                       7f4da3db0000-7f4da3db4000 rw-p 00000000 00:00 0
                       7f4da3db4000-7f4da3ebc000 r-xp 00000000 00:1a 4844910                    /usr/lib64/libm-2.24.so
                       7f4da3ebc000-7f4da40bb000 ---p 00108000 00:1a 4844910                    /usr/lib64/libm-2.24.so
                       7f4da40bb000-7f4da40bc000 r--p 00107000 00:1a 4844910                    /usr/lib64/libm-2.24.so
                       7f4da40bc000-7f4da40bd000 rw-p 00108000 00:1a 4844910                    /usr/lib64/libm-2.24.so
                       7f4da40bd000-7f4da40bf000 r-xp 00000000 00:1a 4844928                    /usr/lib64/libutil-2.24.so
                       7f4da40bf000-7f4da42be000 ---p 00002000 00:1a 4844928                    /usr/lib64/libutil-2.24.so
                       7f4da42be000-7f4da42bf000 r--p 00001000 00:1a 4844928                    /usr/lib64/libutil-2.24.so
                       7f4da42bf000-7f4da42c0000 rw-p 00002000 00:1a 4844928                    /usr/lib64/libutil-2.24.so
                       7f4da42c0000-7f4da42c3000 r-xp 00000000 00:1a 4844908                    /usr/lib64/libdl-2.24.so
                       7f4da42c3000-7f4da44c2000 ---p 00003000 00:1a 4844908                    /usr/lib64/libdl-2.24.so
                       7f4da44c2000-7f4da44c3000 r--p 00002000 00:1a 4844908                    /usr/lib64/libdl-2.24.so
                       7f4da44c3000-7f4da44c4000 rw-p 00003000 00:1a 4844908                    /usr/lib64/libdl-2.24.so
                       7f4da44c4000-7f4da44dc000 r-xp 00000000 00:1a 4844920                    /usr/lib64/libpthread-2.24.so
                       7f4da44dc000-7f4da46dc000 ---p 00018000 00:1a 4844920                    /usr/lib64/libpthread-2.24.so
                       7f4da46dc000-7f4da46dd000 r--p 00018000 00:1a 4844920                    /usr/lib64/libpthread-2.24.so
                       7f4da46dd000-7f4da46de000 rw-p 00019000 00:1a 4844920                    /usr/lib64/libpthread-2.24.so
                       7f4da46de000-7f4da46e2000 rw-p 00000000 00:00 0
                       7f4da46e2000-7f4da4917000 r-xp 00000000 00:1a 5277535                    /usr/lib64/libpython3.5m.so.1.0
                       7f4da4917000-7f4da4b17000 ---p 00235000 00:1a 5277535                    /usr/lib64/libpython3.5m.so.1.0
                       7f4da4b17000-7f4da4b1c000 r--p 00235000 00:1a 5277535                    /usr/lib64/libpython3.5m.so.1.0
                       7f4da4b1c000-7f4da4b7f000 rw-p 0023a000 00:1a 5277535                    /usr/lib64/libpython3.5m.so.1.0
                       7f4da4b7f000-7f4da4baf000 rw-p 00000000 00:00 0
                       7f4da4baf000-7f4da4bd4000 r-xp 00000000 00:1a 4844897                    /usr/lib64/ld-2.24.so
                       7f4da4bdf000-7f4da4c10000 rw-p 00000000 00:00 0
                       7f4da4c10000-7f4da4c61000 r--p 00000000 00:1a 5225117                    /usr/lib/locale/pl_PL.utf8/LC_CTYPE
                       7f4da4c61000-7f4da4d91000 r--p 00000000 00:1a 4844827                    /usr/lib/locale/en_US.utf8/LC_COLLATE
                       7f4da4d91000-7f4da4d95000 rw-p 00000000 00:00 0
                       7f4da4dc1000-7f4da4dc2000 r--p 00000000 00:1a 4844832                    /usr/lib/locale/en_US.utf8/LC_NUMERIC
                       7f4da4dc2000-7f4da4dc3000 r--p 00000000 00:1a 4844795                    /usr/lib/locale/en_US.utf8/LC_TIME
                       7f4da4dc3000-7f4da4dc4000 r--p 00000000 00:1a 4844793                    /usr/lib/locale/en_US.utf8/LC_MONETARY
                       7f4da4dc4000-7f4da4dc5000 r--p 00000000 00:1a 4844830                    /usr/lib/locale/en_US.utf8/LC_MESSAGES/SYS_LC_MESSAGES
                       7f4da4dc5000-7f4da4dc6000 r--p 00000000 00:1a 4844847                    /usr/lib/locale/en_US.utf8/LC_PAPER
                       7f4da4dc6000-7f4da4dc7000 r--p 00000000 00:1a 4844831                    /usr/lib/locale/en_US.utf8/LC_NAME
                       7f4da4dc7000-7f4da4dc8000 r--p 00000000 00:1a 4844790                    /usr/lib/locale/en_US.utf8/LC_ADDRESS
                       7f4da4dc8000-7f4da4dc9000 r--p 00000000 00:1a 4844794                    /usr/lib/locale/en_US.utf8/LC_TELEPHONE
                       7f4da4dc9000-7f4da4dca000 r--p 00000000 00:1a 4844792                    /usr/lib/locale/en_US.utf8/LC_MEASUREMENT
                       7f4da4dca000-7f4da4dd1000 r--s 00000000 00:1a 4845203                    /usr/lib64/gconv/gconv-modules.cache
                       7f4da4dd1000-7f4da4dd2000 r--p 00000000 00:1a 4844791                    /usr/lib/locale/en_US.utf8/LC_IDENTIFICATION
                       7f4da4dd2000-7f4da4dd4000 rw-p 00000000 00:00 0
                       7f4da4dd4000-7f4da4dd5000 r--p 00025000 00:1a 4844897                    /usr/lib64/ld-2.24.so
                       7f4da4dd5000-7f4da4dd6000 rw-p 00026000 00:1a 4844897                    /usr/lib64/ld-2.24.so
                       7f4da4dd6000-7f4da4dd7000 rw-p 00000000 00:00 0
                       7ffd24da1000-7ffd24dc2000 rw-p 00000000 00:00 0                          [stack]
                       7ffd24de8000-7ffd24dea000 r--p 00000000 00:00 0                          [vvar]
                       7ffd24dea000-7ffd24dec000 r-xp 00000000 00:00 0                          [vdso]
                       ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
    COREDUMP_TIMESTAMP=1477877460000000
    MESSAGE=Process 14498 (python3) of user 1002 failed with ZeroDivisionError: division by zero:

            Traceback (most recent call last):
              File "systemd_coredump_exception_handler.py", line 89, in <module>
                g()
              File "systemd_coredump_exception_handler.py", line 88, in g
                f()
              File "systemd_coredump_exception_handler.py", line 86, in f
                div0 = 1 / 0  # pylint: disable=W0612
            ZeroDivisionError: division by zero

            Local variables in innermost frame:
              h=<function f at 0x7f4da3606e18>
              a=3
    _PID=14499
    _SOURCE_REALTIME_TIMESTAMP=1477877460025975