alphabet sour warning

A recently added impossible to check for an(Null) and an("") was
triggered by the fuzzer:  Alphabet soup: 'an("")'.  I reproduced it a
couple of times and tracked it do_screen_description(for '/' command)
matching the symbol from mapglyph to monster class #0, a placeholder
with symbol value '\0'.  So mapglyph() returned a symbol of '\0', but
not necessary from showsyms[0 + SYM_OFF_M].

The pager lookup code's monster loop shouldn't have been attempting
to match against class #0, and since this fix I haven't been able to
reproduce the situation again.  But I also didn't trigger it with a
bunch of temporary checks in mapglyph() so don't know what is really
going on under the hood.

diff --git a/doc/fixes36.2 b/doc/fixes36.2
index 52cf55f1be3d77dd27f32163a928d4848e211930..1f858d9a97ee4a0a901a29be2437c1d32e34a545 100644 (file)
--- a/doc/fixes36.2
+++ b/doc/fixes36.2
@@ -1,4 +1,4 @@
-$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.217 $ $NHDT-Date: 1546129154 2018/12/30 00:19:14 $
+$NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.218 $ $NHDT-Date: 1546144745 2018/12/30 04:39:05 $
 
 This fixes36.2 file is here to capture information about updates in the 3.6.x
 lineage following the release of 3.6.1 in April 2018. Please note, however,
@@ -357,6 +357,10 @@ when built with STATUS_HILITES enabled (the default), gold on status line
        was missing '$' prefix for symset:Blank
 wizard mode ^G, creating a monster of class 'I' yielded impossible "mkclass
        found no class 35 monsters"
+in some unknown circumstance, examining something on the map could match bogus
+       monster class #0 and trigger impossible "Alphabet soup: 'an("")'."
+       (fix avoids the warning but underlying cause is a mystery; noticed
+       with the fuzzer, which swaps symbol sets in and out at random)
 tty: turn off an optimization that is the suspected cause of Windows reported
        partial status lines following level changes
 tty: ensure that current status fields are always copied to prior status

diff --git a/src/pager.c b/src/pager.c
index 2ae5d8074554727f154d903fedbfe424149f6597..5b7f43c4855bd799403beba47090a058e72e70be 100644 (file)
--- a/src/pager.c
+++ b/src/pager.c
@@ -1,4 +1,4 @@
-/* NetHack 3.6 pager.c $NHDT-Date: 1545774524 2018/12/25 21:48:44 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.145 $ */
+/* NetHack 3.6 pager.c $NHDT-Date: 1546144745 2018/12/30 04:39:05 $  $NHDT-Branch: NetHack-3.6.2-beta01 $:$NHDT-Revision: 1.146 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2018. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -861,9 +861,9 @@ struct permonst **for_supplement;
 
     /* Check for monsters */
     if (!iflags.terrainmode || (iflags.terrainmode & TER_MON) != 0) {
-        for (i = 0; i < MAXMCLASSES; i++) {
+        for (i = 1; i < MAXMCLASSES; i++) {
             if (sym == (looked ? showsyms[i + SYM_OFF_M] : def_monsyms[i].sym)
-                && def_monsyms[i].explain) {
+                && def_monsyms[i].explain && *def_monsyms[i].explain) {
                 need_to_look = TRUE;
                 if (!found) {
                     Sprintf(out_str, "%s%s",
@@ -1235,7 +1235,7 @@ coord *click_cc;
         }
 
         found = do_screen_description(cc, (from_screen || clicklook), sym,
-                                  out_str, &firstmatch, &supplemental_pm);
+                                      out_str, &firstmatch, &supplemental_pm);
 
         /* Finally, print out our explanation. */
         if (found) {