I encountered a segfault in Python's call_readline from LLDB on FreeBSD, with libedit. There is a fix for this issue already in readline.c, but under #ifdef __APPLE__

Backtrace:

(lldb) target create "/data/emaste/src/llvm/build/bin/lldb" --core "lldb-3.7.0.core"
Core file '/tank/emaste/projects/lldb-talk/demo/lldb-3.7.0.core' (x86_64) was loaded.
(lldb) bt

• thread Support "bpo-" in Misc/NEWS #1: tid = 0, 0x0000000809706dcd readline.so`call_readline(sys_stdin=0x00000008055d9d10, sys_stdout=0x00000008055d9e40, prompt=0x0000000806eb7854) + 397 at readline.c:1132, name = 'lldb-3.7.0', stop reason = signal SIGSEGV
  • frame #0: 0x0000000809706dcd readline.socall_readline(sys_stdin=0x00000008055d9d10, sys_stdout=0x00000008055d9e40, prompt=0x0000000806eb7854) + 397 at readline.c:1132 frame #1: 0x0000000805c48f1f libpython2.7.so.1PyOS_Readline(sys_stdin=0x00000008055d9d10, sys_stdout=0x00000008055d9e40, prompt=0x0000000806eb7854) + 383 at myreadline.c:207
    frame Rename README to README.rst and enhance formatting #2: 0x0000000805d7f94f libpython2.7.so.1builtin_raw_input(self=0x0000000000000000, args=0x000000080bec1df0) + 639 at bltinmodule.c:2060 frame #3: 0x0000000805cce5c6 libpython2.7.so.1PyCFunction_Call(func=0x00000008007b78d0, arg=0x000000080bec1df0, kw=0x0000000000000000) + 166 at methodobject.c:81
    frame Update Python Software Foundation Copyright Year. #4: 0x0000000805d992aa libpython2.7.so.1call_function(pp_stack=0x00007fffffffbcd0, oparg=1) + 1754 at ceval.c:4033 frame #5: 0x0000000805d93538 libpython2.7.so.1PyEval_EvalFrameEx(f=0x0000000806ecfdf0, throwflag=0) + 51160 at ceval.c:2679
    frame Add Pycharm's .idea directory to gitignore #6: 0x0000000805d86c54 libpython2.7.so.1PyEval_EvalCodeEx(co=0x0000000805a6af60, globals=0x0000000806f9a580, locals=0x0000000000000000, args=0x000000080a06c670, argcount=2, kws=0x000000080a06c680, kwcount=0, defs=0x0000000805aaeda8, defcount=1, closure=0x0000000000000000) + 5284 at ceval.c:3265 frame #7: 0x0000000805d9c2b6 libpython2.7.so.1fast_function(func=0x0000000806f7da38, pp_stack=0x00007fffffffc520, n=2, na=2, nk=0) + 822 at ceval.c:4129
    frame Change some mercurial/ hg.python.org references. #8: 0x0000000805d994c8 libpython2.7.so.1call_function(pp_stack=0x00007fffffffc520, oparg=1) + 2296 at ceval.c:4054 frame #9: 0x0000000805d93538 libpython2.7.so.1PyEval_EvalFrameEx(f=0x000000080a06c4b0, throwflag=0) + 51160 at ceval.c:2679
    frame bpo-29474: Improve documentation for weakref.WeakValueDictionary #10: 0x0000000805d86c54 libpython2.7.so.1PyEval_EvalCodeEx(co=0x0000000805a5ebf0, globals=0x0000000806f9a580, locals=0x0000000000000000, args=0x000000080a06c3e0, argcount=2, kws=0x000000080a06c3f0, kwcount=0, defs=0x0000000805aaecc8, defcount=1, closure=0x0000000000000000) + 5284 at ceval.c:3265 frame #11: 0x0000000805d9c2b6 libpython2.7.so.1fast_function(func=0x0000000806f7d8e8, pp_stack=0x00007fffffffcd70, n=2, na=2, nk=0) + 822 at ceval.c:4129
    frame bpo-29524: Add Objects/call.c file #12: 0x0000000805d994c8 libpython2.7.so.1call_function(pp_stack=0x00007fffffffcd70, oparg=1) + 2296 at ceval.c:4054 frame #13: 0x0000000805d93538 libpython2.7.so.1PyEval_EvalFrameEx(f=0x000000080a06c230, throwflag=0) + 51160 at ceval.c:2679
    frame Disable Travis docs job until a fix is found #14: 0x0000000805d86c54 libpython2.7.so.1PyEval_EvalCodeEx(co=0x0000000805a869e0, globals=0x0000000806f9a580, locals=0x0000000000000000, args=0x000000080a06b9f8, argcount=0, kws=0x000000080a06b9f8, kwcount=2, defs=0x00000008009af688, defcount=3, closure=0x0000000000000000) + 5284 at ceval.c:3265 frame #15: 0x0000000805d9c2b6 libpython2.7.so.1fast_function(func=0x0000000806f7d300, pp_stack=0x00007fffffffd5c0, n=4, na=0, nk=2) + 822 at ceval.c:4129
    frame Make Travis docs build more lenient #16: 0x0000000805d994c8 libpython2.7.so.1call_function(pp_stack=0x00007fffffffd5c0, oparg=512) + 2296 at ceval.c:4054 frame #17: 0x0000000805d93538 libpython2.7.so.1PyEval_EvalFrameEx(f=0x000000080a06b830, throwflag=0) + 51160 at ceval.c:2679
    frame Rename Doc/README.txt to Doc/README.rst #18: 0x0000000805d9c16a libpython2.7.so.1fast_function(func=0x0000000806f9d300, pp_stack=0x00007fffffffdbd0, n=1, na=1, nk=0) + 490 at ceval.c:4119 frame #19: 0x0000000805d994c8 libpython2.7.so.1call_function(pp_stack=0x00007fffffffdbd0, oparg=1) + 2296 at ceval.c:4054
    frame Update link destination of the Mersenne Twister homepage #20: 0x0000000805d93538 libpython2.7.so.1PyEval_EvalFrameEx(f=0x000000080098c9c0, throwflag=0) + 51160 at ceval.c:2679 frame #21: 0x0000000805d86c54 libpython2.7.so.1PyEval_EvalCodeEx(co=0x00000008008ffa90, globals=0x00000008007d8580, locals=0x00000008007d8580, args=0x0000000000000000, argcount=0, kws=0x0000000000000000, kwcount=0, defs=0x0000000000000000, defcount=0, closure=0x0000000000000000) + 5284 at ceval.c:3265
    frame [backport to 3.6] bpo-29474: Improve documentation for weakref.WeakValueDictionary #22: 0x0000000805d857a5 libpython2.7.so.1PyEval_EvalCode(co=0x00000008008ffa90, globals=0x00000008007d8580, locals=0x00000008007d8580) + 85 at ceval.c:667 frame #23: 0x0000000805dd4a15 libpython2.7.so.1run_mod(mod=0x000000080a14f128, filename=0x0000000805e22022, globals=0x00000008007d8580, locals=0x00000008007d8580, flags=0x0000000000000000, arena=0x000000080a027800) + 101 at pythonrun.c:1371
    frame bpo-28837: Fix lib2to3 handling of map/zip/filter #24: 0x0000000805dd50a4 libpython2.7.so.1PyRun_StringFlags(str=0x000000080a0ff820, start=257, globals=0x00000008007d8580, locals=0x00000008007d8580, flags=0x0000000000000000) + 148 at pythonrun.c:1334 frame #25: 0x0000000805dd4f54 libpython2.7.so.1PyRun_SimpleStringFlags(command=0x000000080a0ff820, flags=0x0000000000000000) + 100 at pythonrun.c:975
    frame [backport to 3.5] bpo-29529: Add .travis.yml to 3.5 branch #26: 0x0000000802085fa4 liblldb.so.3.7IOHandlerPythonInterpreter::Run() + 324 frame #27: 0x0000000801f78c12 liblldb.so.3.7lldb_private::Debugger::ExecuteIOHandlers() + 162
    frame bpo-28556: Various updates to typing #28: 0x000000080206635e liblldb.so.3.7lldb_private::CommandInterpreter::RunCommandInterpreter(bool, bool, lldb_private::CommandInterpreterRunOptions&) + 126 frame #29: 0x00000008012bc79f liblldb.so.3.7lldb::SBDebugger::RunCommandInterpreter(bool, bool) + 63
    frame Allow up to a 0.01% drop in coverage #30: 0x0000000000406546 lldbDriver::MainLoop() + 2454 frame #31: 0x0000000000406a17 lldbmain + 439
    frame bpo-29576: Improve some deprecations in the importlib #32: 0x000000000040362f lldb`_start + 367

frame #0: 0x0000000809706dcd readline.so`call_readline(sys_stdin=0x00000008055d9d10, sys_stdout=0x00000008055d9e40, prompt=0x0000000806eb7854) + 397 at readline.c:1132
1129 line = history_get(length + libedit_history_start - 1)->line;
1130 } else
1131 #endif /* __APPLE__ */
-> 1132 line = history_get(length)->line;
1133 else
1134 line = "";
1135 if (strcmp(p, line))

It looks like a straightforward s/#ifdef __APPLE__/#if defined(APPLE) || defined(FreeBSD)/ fixes the issue (as in the attached proof of concept patch).

Presumably the #ifdefs ought to just be deleted though, relying on the runtime detection of libedit compatibility issues on any platform.

See also bpo-13501 for a more platform-independent approach.

I think this crash is actually due to a bug in Editline (later fixed; see bpo-18458), but since Python already has the workaround, it makes sense to use the workaround if necessary for Free BSD, or maybe even in general.

The change in spec in editline was to better match GNU readline behavior. Unfortunately, we depended on the old behavior. Technically, we don't support editline out-of-the-box other than on OS X; as Martin notes, generalizing that support is what bpo-13501 is about. I'm going to close this as a duplicate of it.