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|ID||Project||Category||View Status||Date Submitted||Last Update|
|0000117||mercury||Bug||public||2009-11-28 02:36||2015-10-31 19:04|
|Target Version||Fixed in Version|
|Summary||0000117: No error message for false non_empty_list declaration; runtime segfault|
|Description||(The available "Severity" values aren't quite right for a compiler. I chose "minor" on the grounds that it affects only incorrect programs, though it's among the more serious of this class, in that it still compiles, but the resulting executable segfaults.)|
I have a program where a function's output variable's mode is declared as out(non_empty_list), but where in fact the result can be empty. The program compiles with no warnings (whether with --debug or --grade=hlc.gc), but segfaults when it generates an empty list for a caller that assumes non-emptiness. (I have a feeling that in some cases the executable silently produces wrong results rather than segfaulting, though I'm not certain.)
I haven't yet made a minimal example, but can do so on request.
Tested with rotd-2009-02-26 and a 2007 version.
|Tags||No tags attached.|
|Can you post a test case?|
I've attached two files, nonempty12.m and call_nonempty12.m. The first is the one of interest, in that it compiles without error. The second is the obvious corresponding `main' predicate that segfaults when trying to access the first element of the list.
The test case is remarkably simple, not at all the highly specific circumstances I'd usually have for a Mercury compiler bug; I suppose then that it must be related to one of the several already-known limitations in the current mode system implementation.
I've tested with rotd-2009-02-26 on i686-pc-linux-gnu (Debian), with mgnuc=gcc-3.4.6, with both
`mmc --make --debug call_nonempty12 && ./call_nonempty12' and
`mmc --make --grade=hlc.gc call_nonempty12 && ./call_nonempty12'.
(Also tested with rotd-2007-12-16, so it's fairly long-standing.)
The problem is the following XXX.
inst_matches_final_3(ground(UniqA, HOInstInfoA), bound(UniqB, ListB),
MaybeType, !Info) :-
ModuleInfo = !.Info ^ imi_module_info,
\+ ho_inst_info_is_nonstandard_func_mode(ModuleInfo, HOInstInfoA),
bound_inst_list_is_ground(ListB, MaybeType, ModuleInfo),
uniq_matches_bound_inst_list(UniqA, ListB, ModuleInfo),
MaybeType = yes(Type),
% We can only do this check if the type is known.
bound_inst_list_is_complete_for_type(set.init, ModuleInfo, ListB, Type)
% XXX enabling the check for bound_inst_list_is_complete
% for type makes the mode checker too conservative in
% the absence of alias tracking, so we currently always
% succeed, even if this check fails.
This was fixed in commit 491bb0a.
(I have added a test case for it.)
|2009-11-28 02:36||pjrm||New Issue|
|2009-12-01 01:53||wangp||Note Added: 0000220|
|2009-12-01 03:02||pjrm||File Added: nonempty12.m|
|2009-12-01 03:03||pjrm||File Added: call_nonempty12.m|
|2009-12-01 03:13||pjrm||Note Added: 0000222|
|2009-12-01 21:35||wangp||Note Added: 0000223|
|2009-12-11 06:47||juliensf||Status||new => confirmed|
|2015-10-31 19:04||juliensf||Note Added: 0000858|
|2015-10-31 19:04||juliensf||Status||confirmed => resolved|
|2015-10-31 19:04||juliensf||Resolution||open => fixed|
|2015-10-31 19:04||juliensf||Assigned To||=> juliensf|