Re: mg: crash on re-search with a file containing an empty line

[Theo Buehler]

> Can this patch get committed in the current form?

I don't mind committing either version of the patch.

Unless I hear objections, I'm going to commit the patch below soon.

Index: re_search.c
===================================================================
RCS file: /var/cvs/src/usr.bin/mg/re_search.c,v
retrieving revision 1.33
diff -u -p -r1.33 re_search.c
--- re_search.c 6 Aug 2017 04:39:45 -0000       1.33
+++ re_search.c 8 Jul 2020 13:00:40 -0000
@@ -332,8 +332,8 @@ re_forwsrch(void)
        while (clp != (curbp->b_headp)) {
                regex_match[0].rm_so = tbo;
                regex_match[0].rm_eo = llength(clp);
-               error = regexec(&regex_buff, ltext(clp), RE_NMATCH, regex_match,
-                   REG_STARTEND);
+               error = regexec(&regex_buff, ltext(clp) ? ltext(clp) : "",
+                   RE_NMATCH, regex_match, REG_STARTEND);
                if (error != 0) {
                        clp = lforw(clp);
                        tdotline++;
@@ -389,8 +389,9 @@ re_backsrch(void)
                 * do this character-by-character after the first match since
                 * POSIX regexps don't give you a way to do reverse matches.
                 */
-               while (!regexec(&regex_buff, ltext(clp), RE_NMATCH, regex_match,
-                   REG_STARTEND) && regex_match[0].rm_so < tbo) {
+               while (!regexec(&regex_buff, ltext(clp) ? ltext(clp) : "",
+                   RE_NMATCH, regex_match, REG_STARTEND) &&
+                   regex_match[0].rm_so <= tbo) {
                        memcpy(&lastmatch, &regex_match[0], sizeof(regmatch_t));
                        regex_match[0].rm_so++;
                        regex_match[0].rm_eo = llength(clp);
@@ -538,8 +539,8 @@ killmatches(int cond)
                /* see if line matches */
                regex_match[0].rm_so = 0;
                regex_match[0].rm_eo = llength(clp);
-               error = regexec(&regex_buff, ltext(clp), RE_NMATCH, regex_match,
-                   REG_STARTEND);
+               error = regexec(&regex_buff, ltext(clp) ? ltext(clp) : "",
+                   RE_NMATCH, regex_match, REG_STARTEND);
 
                /* Delete line when appropriate */
                if ((cond == FALSE && error) || (cond == TRUE && !error)) {
@@ -613,8 +614,8 @@ countmatches(int cond)
                /* see if line matches */
                regex_match[0].rm_so = 0;
                regex_match[0].rm_eo = llength(clp);
-               error = regexec(&regex_buff, ltext(clp), RE_NMATCH, regex_match,
-                   REG_STARTEND);
+               error = regexec(&regex_buff, ltext(clp) ? ltext(clp) : "",
+                   RE_NMATCH, regex_match, REG_STARTEND);
 
                /* Count line when appropriate */
                if ((cond == FALSE && error) || (cond == TRUE && !error))