'_tolower' has undefined behaviour for many characters, see <https://linux.die.net/man/3/_tolower>.
Also, 'tolower' has undefined behaviour if its argument is not in the range 0..UCHAR_MAX, see <https://pubs.opengroup.org/onlinepubs/9699919799/functions/tolower.html> This patch fixes argp-help.c accordingly. This patch was already applied on 2009-09-28, but was reverted on 2016-04-03 through https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=14a582531cef13c855c9e9638aac630c0a43ae37 The 2016-04-03 patch also reverted 1) https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=ec2348da1754e807233e33beefdb732a119e4adc reinstalled through https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=a50e906c0c046c57938f786ffb82b36beea75043 2) https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=2457d7ca6856f84502b09fa4690f6f4187de050f reinstalled through https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=5297992f06027a12671c52ab258eb3fb337972aa 2020-12-08 Bruno Haible <[email protected]> argp: Don't rely on undefined behaviour of _tolower(). Patch by Eric Blake <https://lists.gnu.org/archive/html/bug-gnulib/2009-09/msg00287.html>. * lib/argp-help.c (hol_entry_cmp): Don't use _tolower on values that are not upper-case. Pass correct range to tolower. diff --git a/lib/argp-help.c b/lib/argp-help.c index 52260f3..03fc6c7 100644 --- a/lib/argp-help.c +++ b/lib/argp-help.c @@ -789,13 +789,11 @@ hol_entry_cmp (const struct hol_entry *entry1, first, but as they're not displayed, it doesn't matter where they are. */ { - char first1 = short1 ? short1 : long1 ? *long1 : 0; - char first2 = short2 ? short2 : long2 ? *long2 : 0; -#ifdef _tolower - int lower_cmp = _tolower (first1) - _tolower (first2); -#else + unsigned char first1 = short1 ? short1 : long1 ? *long1 : 0; + unsigned char first2 = short2 ? short2 : long2 ? *long2 : 0; + /* Use tolower, not _tolower, since the latter has undefined + behaviour for characters that are not uppercase letters. */ int lower_cmp = tolower (first1) - tolower (first2); -#endif /* Compare ignoring case, except when the options are both the same letter, in which case lower-case always comes first. */ return lower_cmp ? lower_cmp : first2 - first1;
