I have been able to create a local debug build C-C TB with gcc-10. But caveat emptor. I apply rather strict checking at compile time and abort compilation. I think I have applied the following flags to CXXFLAGS and CFLAGS during compilation. -Werror -Wsign-compare -Wunused-result -Wunused-variable -Wformat The configure script whitelists some warnings by adding -Wno-error=... flags explicitly from what I see the real flags used during build. With this strict checking I notice many dubious code both in M-C and C-C (many in ldap code). But the strict compile-time checking of snprintf() string buffer overflow of GCC-10 has a bug. I need to apply the following local patch to create the debug build of C-C TB locally with the said flags. # HG changeset patch # User ISHIKAWA, Chiaki <ishikawa@yk.rim.or.jp> # Parent  c989a1970f120c98cba1bb2010b81d87308ea2d7 avoid gcc snprintf format string check bug. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98281 diff --git a/calendar/libical/src/libical/icalvalue.c b/calendar/libical/src/libical/icalvalue.c --- a/calendar/libical/src/libical/icalvalue.c +++ b/calendar/libical/src/libical/icalvalue.c @@ -872,21 +872,28 @@ static char* icalvalue_utcoffset_as_ical      } else {      sign = '-';      }      h = data/3600;      m = (data - (h*3600))/ 60;      s = (data - (h*3600) - (m*60)); -    if (s > 0) -    snprintf(str,9,"%c%02d%02d%02d",sign,abs(h),abs(m),abs(s)); -    else -    snprintf(str,9,"%c%02d%02d",sign,abs(h),abs(m)); - +    if ((0 <= m && m <= 60) && (0 <= s && s <= 60) && (0 <= abs(h) && abs(h) <= 24)) { +        if (s > 0) + snprintf(str,9,"%c%02d%02d%02d",sign,abs(h),abs(m),abs(s)); +        else +            snprintf(str,9,"%c%02d%02d",sign,abs(h),abs(m)); +    } else    { +#ifdef DEBUG +        icalerror_assert((0 <= m && m <= 60) && +                         (0 <= s && s <= 60) && (0 <= abs(h) && abs(h) <=24) , +                         "Minutes & seconds must be in [0, 60) abs(h) must be in [0, 24)"); +#endif +    }      return str;  }  static char* icalvalue_string_as_ical_string_r(const icalvalue* value) {      const char* data;      char* str = 0;      icalerror_check_arg_rz( (value!=0),"value"); Withtou the patch, the above code produced a possible buffer overflow warning and fails with -Werror flag. Obviously, the compile value propagation somewhere went wrong. A similar bug was reported early this year against gcc-9, but that seems to have been fixed. However, obviously gcc-10 resurfaced the bug in a slightly different place. Just  thought to share this. Chiaki