[groff] 01/01: src/roff/troff/input.cpp: Hush compiler warning.

[G. Branden Robinson]

gbranden pushed a commit to branch master
in repository groff.

commit fca2b723e7f1dc65057841e9eefc5b074786c4e1
Author: G. Branden Robinson <address@hidden>
Date:   Tue Nov 6 05:53:52 2018 -0500

    src/roff/troff/input.cpp: Hush compiler warning.
    
        * src/roff/troff/input.cpp (macro_source): GCC 8 dislikes it,
        throwing a stringop-overflow warning, when the length argument
        to strncat() is computed based on the length of the source
        argument rather than the destination.  It's a reasonable
        warning, but GCC is not smart enough to discern that our
        destination string was allocated based on the length of a
        superset of the source string, and so cannot overflow.
    
        GCC 8 is not fooled if the length of the source string is
        computed in the same basic block as the strncat(), but it is
        if we lift it outside.  This has the side benefit of slightly
        greater efficiency in that we compute strlen(fn) only once
        instead of up to three times in the case that someone does an
        .mso of "foobar.tmac" but that file is not present and
        "tmac.foobar" is attempted instead.
    
        For background, see
        
<https://www.us-cert.gov/bsi/articles/knowledge/coding-practices/strncpy-and-strncat>.
    
        Fixes <https://savannah.gnu.org/bugs/index.php?54968>.
    
    Signed-off-by: G. Branden Robinson <address@hidden>
---
 src/roff/troff/input.cpp | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/roff/troff/input.cpp b/src/roff/troff/input.cpp
index fbffe38..6af7a03 100644
--- a/src/roff/troff/input.cpp
+++ b/src/roff/troff/input.cpp
@@ -7701,19 +7701,20 @@ void macro_source()
     // FOOBAR.tmac and vice versa
     if (!fp) {
       const char *fn = nm.contents();
+      int fnlen = strlen(fn);
       if (strncasecmp(fn, MACRO_PREFIX, sizeof(MACRO_PREFIX) - 1) == 0) {
-       char *s = new char[strlen(fn) + sizeof(MACRO_POSTFIX)];
+       char *s = new char[fnlen + sizeof(MACRO_POSTFIX)];
        strcpy(s, fn + sizeof(MACRO_PREFIX) - 1);
        strcat(s, MACRO_POSTFIX);
        fp = mac_path->open_file(s, &path);
        a_delete s;
       }
       if (!fp) {
-       if (strncasecmp(fn + strlen(fn) - sizeof(MACRO_POSTFIX) + 1,
+       if (strncasecmp(fn + fnlen - sizeof(MACRO_POSTFIX) + 1,
                        MACRO_POSTFIX, sizeof(MACRO_POSTFIX) - 1) == 0) {
-         char *s = new char[strlen(fn) + sizeof(MACRO_PREFIX)];
+         char *s = new char[fnlen + sizeof(MACRO_PREFIX)];
          strcpy(s, MACRO_PREFIX);
-         strncat(s, fn, strlen(fn) - sizeof(MACRO_POSTFIX) + 1);
+         strncat(s, fn, fnlen - sizeof(MACRO_POSTFIX) + 1);
          fp = mac_path->open_file(s, &path);
          a_delete s;
        }