LC_COLLATE: Fix last character ellipsis handling (Bug 22668)

  From: Hanataka Shinya <hanataka.shinya@gmail.com>

During ellipsis processing the collation cursor was not correctly
moved to the end of the ellipsis after processing.

The code inserted the new entry after the cursor, but before the
real end of the ellipsis:
                                [cursor]
... element_t <-> element_t <-> element_t <-> element_t
                  "<U0000>"     "<U0001>"     "<U007F>"
                  startp                      endp

At the end of the function we have:

                  [cursor]
... element_t <-> element_t <-> element_t
                  "<U007E>"     "<U007F>"
                                endp

The cursor should be pointing at endp, the last element in the
doubly-linked list, otherwise when execution returns to the
caller we will start inserting the next line after <U007E>.

Subsequent operations end up unlinking the ellipsis end entry or
just leaving it in the list dangling from the end.  This kind of
dangling is immediately visible in C.UTF-8 with the following
sorting from strcoll:
<U0010FFFF>
<U0000FFFF>
<U000007FF>
<U0000007F>

With the cursor correctly adjusted the end entry is correctly given
the right location and thus the right weight.

No regressions on x86_64 and i686.

Co-authored-by: Carlos O'Donell <carlos@redhat.com>
---
 locale/programs/ld-collate.c | 3 +++
 1 file changed, 3 insertions(+)
  

* Carlos O'Donell via Libc-alpha:

> From: Hanataka Shinya <hanataka.shinya@gmail.com>
>
> During ellipsis processing the collation cursor was not correctly
> moved to the end of the ellipsis after processing.
>
> The code inserted the new entry after the cursor, but before the
> real end of the ellipsis:
>                                 [cursor]
> ... element_t <-> element_t <-> element_t <-> element_t
>                   "<U0000>"     "<U0001>"     "<U007F>"
>                   startp                      endp
>
> At the end of the function we have:
>
>                   [cursor]
> ... element_t <-> element_t <-> element_t
>                   "<U007E>"     "<U007F>"
>                                 endp
>
> The cursor should be pointing at endp, the last element in the
> doubly-linked list, otherwise when execution returns to the
> caller we will start inserting the next line after <U007E>.
>
> Subsequent operations end up unlinking the ellipsis end entry or
> just leaving it in the list dangling from the end.  This kind of
> dangling is immediately visible in C.UTF-8 with the following
> sorting from strcoll:
> <U0010FFFF>
> <U0000FFFF>
> <U000007FF>
> <U0000007F>
>
> With the cursor correctly adjusted the end entry is correctly given
> the right location and thus the right weight.
>
> No regressions on x86_64 and i686.
>
> Co-authored-by: Carlos O'Donell <carlos@redhat.com>
> ---
>  locale/programs/ld-collate.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/locale/programs/ld-collate.c b/locale/programs/ld-collate.c
> index 0af21e05e2..b6406b775d 100644
> --- a/locale/programs/ld-collate.c
> +++ b/locale/programs/ld-collate.c
> @@ -1483,6 +1483,9 @@ order for `%.*s' already defined at %s:%Zu"),
>  	    }
>  	}
>      }
> +  /* Move the cursor to the last entry in the ellipsis.
> +     Subsequent operations need to start from the last entry.  */
> +  collate->cursor = endp;
>  }

I do not completely understand the code, but I double-checked a few
things, and this looks consistent.  So I guess it's okay to check this
in.

Thanks,
Florian
  

On 3/1/21 12:18 PM, Florian Weimer wrote:
> * Carlos O'Donell via Libc-alpha:
> 
>> From: Hanataka Shinya <hanataka.shinya@gmail.com>
>>
>> During ellipsis processing the collation cursor was not correctly
>> moved to the end of the ellipsis after processing.
>>
>> The code inserted the new entry after the cursor, but before the
>> real end of the ellipsis:
>>                                 [cursor]
>> ... element_t <-> element_t <-> element_t <-> element_t
>>                   "<U0000>"     "<U0001>"     "<U007F>"
>>                   startp                      endp
>>
>> At the end of the function we have:
>>
>>                   [cursor]
>> ... element_t <-> element_t <-> element_t
>>                   "<U007E>"     "<U007F>"
>>                                 endp
>>
>> The cursor should be pointing at endp, the last element in the
>> doubly-linked list, otherwise when execution returns to the
>> caller we will start inserting the next line after <U007E>.
>>
>> Subsequent operations end up unlinking the ellipsis end entry or
>> just leaving it in the list dangling from the end.  This kind of
>> dangling is immediately visible in C.UTF-8 with the following
>> sorting from strcoll:
>> <U0010FFFF>
>> <U0000FFFF>
>> <U000007FF>
>> <U0000007F>
>>
>> With the cursor correctly adjusted the end entry is correctly given
>> the right location and thus the right weight.
>>
>> No regressions on x86_64 and i686.
>>
>> Co-authored-by: Carlos O'Donell <carlos@redhat.com>
>> ---
>>  locale/programs/ld-collate.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/locale/programs/ld-collate.c b/locale/programs/ld-collate.c
>> index 0af21e05e2..b6406b775d 100644
>> --- a/locale/programs/ld-collate.c
>> +++ b/locale/programs/ld-collate.c
>> @@ -1483,6 +1483,9 @@ order for `%.*s' already defined at %s:%Zu"),
>>  	    }
>>  	}
>>      }
>> +  /* Move the cursor to the last entry in the ellipsis.
>> +     Subsequent operations need to start from the last entry.  */
>> +  collate->cursor = endp;
>>  }
> 
> I do not completely understand the code, but I double-checked a few
> things, and this looks consistent.  So I guess it's okay to check this
> in.

Re-tested again, no regressions. Pushed. Thanks.