Uninitialized memory when running tests with valgrind: regmatch.rm_ic not initialized

[dpelle]

Describe the bug

Valgrind detects use of uninitialized memory when running vim tests.

To Reproduce

Build vim with valgrind run this test:

$ cd vim/src/tesdir
$ make test_breakindent

File valgrind.test_breakindent then contains:

==10483== Memcheck, a memory error detector
==10483== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==10483== Using Valgrind-3.17.0.GIT and LibVEX; rerun with -h for copyright info
==10483== Command: ../vim -f -u unix.vim -U NONE --noplugin --not-a-term -S runtest.vim test_breakindent.vim --cmd au\ SwapExists\ *\ let\ v:swapchoice\ =\ "e"
==10483== Parent PID: 10482
==10483== 
==10483== Conditional jump or move depends on uninitialised value(s)
==10483==    at 0x57A1A3: nfa_regmatch (regexp_nfa.c:6492)
==10483==    by 0x579145: nfa_regtry (regexp_nfa.c:7236)
==10483==    by 0x579145: nfa_regexec_both (regexp_nfa.c:7431)
==10483==    by 0x538598: vim_regexec_string (regexp.c:2799)
==10483==    by 0x4BD7AE: get_breakindent_win (indent.c:956)
==10483==    by 0x671C00: win_lbr_chartabsize (charset.c:1137)
==10483==    by 0x6715A2: win_linetabsize (charset.c:821)
==10483==    by 0x4E7613: plines_win_nofold (misc1.c:400)
==10483==    by 0x4E755E: plines_win_nofill (misc1.c:380)
==10483==    by 0x4F2494: comp_botline (move.c:83)
==10483==    by 0x4F0EEE: validate_botline_win (move.c:610)
==10483==    by 0x4F0EEE: validate_botline (move.c:600)
==10483==    by 0x4F0EEE: update_topline (move.c:316)
==10483==    by 0x4F2696: curs_columns (move.c:959)
==10483==    by 0x47C05C: ex_redraw (ex_docmd.c:8117)
==10483==    by 0x475D7E: do_one_cmd (ex_docmd.c:2610)
==10483==    by 0x475D7E: do_cmdline (ex_docmd.c:999)
==10483==    by 0x613C0B: call_user_func (userfunc.c:2699)
==10483==    by 0x613C0B: call_user_func_check (userfunc.c:2846)
==10483==    by 0x612791: call_func (userfunc.c:3336)
==10483==    by 0x6120D1: get_func_tv (userfunc.c:1707)
==10483==    by 0x619D09: ex_call (userfunc.c:4971)
==10483==    by 0x475D7E: do_one_cmd (ex_docmd.c:2610)
==10483==    by 0x475D7E: do_cmdline (ex_docmd.c:999)
==10483==    by 0x454BD5: ex_execute (eval.c:6247)
==10483==    by 0x475D7E: do_one_cmd (ex_docmd.c:2610)
==10483==    by 0x475D7E: do_cmdline (ex_docmd.c:999)
==10483==    by 0x613C0B: call_user_func (userfunc.c:2699)
==10483==    by 0x613C0B: call_user_func_check (userfunc.c:2846)
==10483==    by 0x612791: call_func (userfunc.c:3336)
==10483==    by 0x6120D1: get_func_tv (userfunc.c:1707)
==10483==    by 0x619D09: ex_call (userfunc.c:4971)
==10483==    by 0x475D7E: do_one_cmd (ex_docmd.c:2610)
==10483==    by 0x475D7E: do_cmdline (ex_docmd.c:999)
==10483==    by 0x5A2516: do_source (scriptfile.c:1406)
==10483==    by 0x5A1CA8: cmd_source (scriptfile.c:971)
==10483==    by 0x475D7E: do_one_cmd (ex_docmd.c:2610)
==10483==    by 0x475D7E: do_cmdline (ex_docmd.c:999)
==10483==    by 0x677DCC: exe_commands (main.c:3081)
==10483==    by 0x677DCC: vim_main2 (main.c:773)
==10483==    by 0x676F55: main (main.c:425)
==10483==  Uninitialised value was created by a stack allocation
==10483==    at 0x4BD5A0: get_breakindent_win (indent.c:906)
==10483== 
(more errors after that)

You need to add the valgrind --track-origins=yes option to see that the uninitialize memory comes from the stack of function get_breakindent_win.

The following patch avoids the valgrind error, but I'm not sure whether it's correct. At least it should give a clue as to how to properly fix it:

$ diff --git a/src/indent.c b/src/indent.c
index 99951c81b..6f4b2476d 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -949,6 +949,7 @@ get_breakindent_win(
     {
        regmatch_T          regmatch;
 
+       regmatch.rm_ic = FALSE;
        regmatch.regprog = vim_regcomp(curbuf->b_p_flp,
                                   RE_MAGIC + RE_STRING + RE_AUTO + RE_STRICT);
        if (regmatch.regprog != NULL)

Environment

• Vim version 8.2.3377
• OS: xubuntu-18.04.5