[PATCH v2] libio: Fix wrong reference to byte stream

[Carlos O'Donell]

On 3/23/26 1:17 PM, Rocket Ma wrote:
> * libio/wgenops.c: Fix _IO_wdefault_pbackfail and _IO_wdefault_finish by
> deferencing wide stream pointers, should be a mistake (bug 33998[1] and
> bug 33999[2])

Please split the patch to only fix one at a time.

For example 33999 is being discussed here with a test case:
https://inbox.sourceware.org/libc-alpha/20260403015721.343918-1-gaoxiang@kylinos.cn/

> The regression test attached can not perform fclose, see bug 34020[3]

Andreas Schwab commented on this one.

> 
> [1]: https://sourceware.org/bugzilla/show_bug.cgi?id=33998
> [2]: https://sourceware.org/bugzilla/show_bug.cgi?id=33999
> [3]: https://sourceware.org/bugzilla/show_bug.cgi?id=34020
> 
> Signed-off-by: Rocket Ma <marocketbd@gmail.com>
> ---
>   libio/Makefile      |  1 +
>   libio/bug-wgenops.c | 30 ++++++++++++++++++++++++++++++
>   libio/wgenops.c     |  8 ++++----
>   3 files changed, 35 insertions(+), 4 deletions(-)
>   create mode 100644 libio/bug-wgenops.c
> 
> diff --git a/libio/Makefile b/libio/Makefile
> index 08e1e0ec25..da838cdecc 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -84,6 +84,7 @@ tests = \
>     bug-ungetwc1 \
>     bug-ungetwc2 \
>     bug-wfflush \
> +  bug-wgenops \
>     bug-wmemstream1 \
>     bug-wsetpos \
>     test-fmemopen \
> diff --git a/libio/bug-wgenops.c b/libio/bug-wgenops.c
> new file mode 100644
> index 0000000000..cf67b9d436
> --- /dev/null
> +++ b/libio/bug-wgenops.c
> @@ -0,0 +1,30 @@

May you please add a copyright header for the test case please?

We license the test cases with a matching project license.

May you please add a line at the top that describes the test.

Example:
/* Bug XXXX: Test XXXX does YYYY.
    Copyright The GNU Toolchain Authors.
    This file is part of the GNU C Library.

    The GNU C Library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    The GNU C Library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */


> +#include <stdio.h>
> +#include <wchar.h>
> +#include <stdlib.h>
> +
> +#define tst_assert(cond)                                                      \
> +  if (!(cond))                                                                \
> +    {                                                                         \
> +      puts ("Failed assertion: " #cond);                                      \
> +      return 1;                                                               \
> +    }

Please see the support/* directory and #include <support/check.h> for TEST_VERIFY.

> +
> +static int
> +do_test (void)
> +{
> +  wchar_t *buf = NULL;
> +  size_t size = 0;
> +  FILE *fp = open_wmemstream (&buf, &size);
> +  tst_assert (fp != NULL);

These should be TEST_VERIFY(...);

> +  tst_assert (fputwc (L'A', fp) != WEOF);
> +  tst_assert (fflush (fp) == 0);
> +
> +  tst_assert (fgetwc (fp) == L'A');
> +  tst_assert (ungetwc (L'B', fp) == L'B');
> +
> +  // fclose (fp); // See BZ 34020; flose will free invalid _IO_save_base
> +  free (buf);
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>

OK. Good use of the support test driver.

> diff --git a/libio/wgenops.c b/libio/wgenops.c
> index 064d71266d..3ebbb941f0 100644
> --- a/libio/wgenops.c
> +++ b/libio/wgenops.c
> @@ -110,8 +110,8 @@ _IO_wdefault_pbackfail (FILE *fp, wint_t c)
>   {
>     if (fp->_wide_data->_IO_read_ptr > fp->_wide_data->_IO_read_base
>         && !_IO_in_backup (fp)
> -      && (wint_t) fp->_IO_read_ptr[-1] == c)
> -    --fp->_IO_read_ptr;
> +      && (wint_t) fp->_wide_data->_IO_read_ptr[-1] == c)

OK. This is the relevant change to use the correct buffer.

> +    --fp->_wide_data->_IO_read_ptr;
>     else
>       {
>         /* Need to handle a filebuf in write mode (switch to read mode). FIXME!*/
> @@ -181,10 +181,10 @@ _IO_wdefault_finish (FILE *fp, int dummy)
>     for (mark = fp->_markers; mark != NULL; mark = mark->_next)
>       mark->_sbuf = NULL;
>   
> -  if (fp->_IO_save_base)
> +  if (fp->_wide_data->_IO_save_base)
>       {
>         free (fp->_wide_data->_IO_save_base);
> -      fp->_IO_save_base = NULL;
> +      fp->_wide_data->_IO_save_base = NULL;

This is being fixed in a different way by Gao Xiang in:
https://inbox.sourceware.org/libc-alpha/20260403015721.343918-1-gaoxiang@kylinos.cn/

>       }
>   
>   #ifdef _IO_MTSAFE_IO


-- 
Cheers,
Carlos.