[PATCH v4 2/2] libio: Ignore doallocate for open_memstream and open_wmemstream [BZ #34019]
Adhemerval Zanella Netto
adhemerval.zanella@linaro.org
Thu May 7 13:49:07 GMT 2026
On 07/05/26 06:40, Gao Xiang wrote:
> From: Xiang Gao <gaoxiang@kylinos.cn>
>
> setvbuf (stream, NULL, _IOFBF, 0) takes a special path in
> _IO_setvbuf: if the byte-oriented buffer base is NULL, it calls
> _IO_DOALLOCATE and returns without invoking the stream setbuf hook.
>
> For open_wmemstream, the byte-oriented buffer base is NULL although
> the wide result buffer has already been initialized in _wide_data.
> As a result, this path calls _IO_wdefault_doallocate, which may
> replace the wide buffer managed by open_wmemstream.
>
> Install an open_wmemstream-specific doallocate hook that leaves
> the growable result buffer unchanged. Add a regression test for this
> path.
>
> Install a narrow memstream doallocate hook as well. It keeps both
> memstream vtables consistent (generic stdio allocation must not
> replace the growable result buffer).
>
> Signed-off-by: Xiang Gao <gaoxiang@kylinos.cn>
The patch looks good, some minor comments below.
> ---
> libio/Makefile | 2 +
> libio/libioP.h | 3 ++
> libio/memstream.c | 10 ++++
> libio/tst-memstream-setvbuf-doallocate.c | 61 +++++++++++++++++++++++
> libio/tst-wmemstream-setvbuf-doallocate.c | 20 ++++++++
> libio/vtables.c | 6 ++-
> libio/wmemstream.c | 10 ++++
> 7 files changed, 110 insertions(+), 2 deletions(-)
> create mode 100644 libio/tst-memstream-setvbuf-doallocate.c
> create mode 100644 libio/tst-wmemstream-setvbuf-doallocate.c
>
> diff --git a/libio/Makefile b/libio/Makefile
> index 6b56567d44..e165a8b4cb 100644
> --- a/libio/Makefile
> +++ b/libio/Makefile
> @@ -117,6 +117,7 @@ tests = \
> tst-fwrite-error \
> tst-getdelim \
> tst-memstream-setbuf \
> + tst-memstream-setvbuf-doallocate \
> tst-memstream1 \
> tst-memstream2 \
> tst-memstream3 \
> @@ -141,6 +142,7 @@ tests = \
> tst-wfiledoallocate-static \
> tst-widetext \
> tst-wmemstream-setbuf \
> + tst-wmemstream-setvbuf-doallocate \
> tst-wmemstream1 \
> tst-wmemstream2 \
> tst-wmemstream3 \
> diff --git a/libio/libioP.h b/libio/libioP.h
> index 17c0b6e76d..fa547a4a29 100644
> --- a/libio/libioP.h
> +++ b/libio/libioP.h
> @@ -742,10 +742,13 @@ extern int _IO_mem_sync (FILE *fp) __THROW attribute_hidden;
> extern void _IO_mem_finish (FILE *fp, int) __THROW attribute_hidden;
> extern FILE *_IO_mem_setbuf (FILE *fp, char *buf, ssize_t size)
> __THROW attribute_hidden;
> +extern int _IO_mem_doallocate (FILE *fp) __THROW attribute_hidden;
> +
> extern int _IO_wmem_sync (FILE *fp) __THROW attribute_hidden;
> extern void _IO_wmem_finish (FILE *fp, int) __THROW attribute_hidden;
> extern FILE *_IO_wmem_setbuf (FILE *fp, char *buf, ssize_t size)
> __THROW attribute_hidden;
> +extern int _IO_wmem_doallocate (FILE *fp) __THROW attribute_hidden;
>
> /* Other strfile functions */
> struct _IO_strfile_;
> diff --git a/libio/memstream.c b/libio/memstream.c
> index 739080e96a..3ba7bcb28b 100644
> --- a/libio/memstream.c
> +++ b/libio/memstream.c
> @@ -122,3 +122,13 @@ _IO_mem_setbuf (FILE *fp, char *p, ssize_t len)
> (void) len;
> return fp;
> }
> +
> +
> +int
> +_IO_mem_doallocate (FILE *fp)
> +{
> + /* Memstream manage a growable buffer internally. The doallocate
> + hook must not replace it with a generic stdio buffer. */
> + (void) fp;
No need the cast here.
> + return 1;
> +}
> diff --git a/libio/tst-memstream-setvbuf-doallocate.c b/libio/tst-memstream-setvbuf-doallocate.c
> new file mode 100644
> index 0000000000..4910f02d5c
> --- /dev/null
> +++ b/libio/tst-memstream-setvbuf-doallocate.c
> @@ -0,0 +1,61 @@
> +/* Test setvbuf on open_memstream, BZ #34019.
> + Copyright (C) 2026 Free Software Foundation, Inc.
> + 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 <libio/tst-memstream.h>
> +
> +static int
> +do_test (void)
> +{
> + /* Regression test for setvbuf doallocate on open_memstream and
> + open_wmemstream. This test covers the _IO_setvbuf path for:
Minor style nit: double space after period.
> +
> + setvbuf (stream, NULL, _IOFBF, 0)
> +
> + This path may call _IO_DOALLOCATE and return without invoking
> + the stream setbuf hook. The generic doallocate hook must not
> + replace the growable result buffer. */
> +
> + CHAR_T *buf = NULL;
> + size_t len = 0;
> + FILE *fp = OPEN_MEMSTREAM (&buf, &len);
> +
> + TEST_VERIFY_EXIT (fp != NULL);
> +
> + TEST_COMPARE (setvbuf (fp, NULL, _IOFBF, 0), 0);
> +
> + TEST_COMPARE (FPUTC (W('A'), fp), W('A'));
> + TEST_COMPARE (fflush (fp), 0);
> + TEST_COMPARE (len, 1);
> + TEST_VERIFY_EXIT (buf != NULL);
> + TEST_VERIFY (buf[0] == W('A'));
> + TEST_VERIFY (buf[1] == W('\0'));
> +
> + TEST_COMPARE (FPUTC (W('B'), fp), W('B'));
> + TEST_COMPARE (fclose (fp), 0);
> + TEST_COMPARE (len, 2);
> + TEST_VERIFY_EXIT (buf != NULL);
> + TEST_VERIFY (buf[0] == W('A'));
> + TEST_VERIFY (buf[1] == W('B'));
> + TEST_VERIFY (buf[2] == W('\0'));
> +
> + free (buf);
> +
> + return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/libio/tst-wmemstream-setvbuf-doallocate.c b/libio/tst-wmemstream-setvbuf-doallocate.c
> new file mode 100644
> index 0000000000..857239aa85
> --- /dev/null
> +++ b/libio/tst-wmemstream-setvbuf-doallocate.c
> @@ -0,0 +1,20 @@
> +/* Test setvbuf on open_wmemstream, BZ #34019.
> + Copyright (C) 2026 Free Software Foundation, Inc.
> + 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/>. */
> +
> +#define TEST_WCHAR
> +#include <libio/tst-memstream-setvbuf-doallocate.c>
> diff --git a/libio/vtables.c b/libio/vtables.c
> index ca9f1b2dc4..ba3f9566f8 100644
> --- a/libio/vtables.c
> +++ b/libio/vtables.c
> @@ -79,10 +79,12 @@
> # pragma weak _IO_mem_finish
> # pragma weak _IO_mem_setbuf
> # pragma weak _IO_mem_sync
> +# pragma weak _IO_mem_doallocate
>
> # pragma weak _IO_wmem_finish
> # pragma weak _IO_wmem_setbuf
> # pragma weak _IO_wmem_sync
> +# pragma weak _IO_wmem_doallocate
>
> # pragma weak __printf_buffer_as_file_overflow
> # pragma weak __printf_buffer_as_file_xsputn
> @@ -338,7 +340,7 @@ const struct _IO_jump_t __io_vtables[] attribute_relro =
> JUMP_INIT (seekpos, _IO_default_seekpos),
> JUMP_INIT (setbuf, _IO_mem_setbuf),
> JUMP_INIT (sync, _IO_mem_sync),
> - JUMP_INIT (doallocate, _IO_default_doallocate),
> + JUMP_INIT (doallocate, _IO_mem_doallocate),
> JUMP_INIT (read, _IO_default_read),
> JUMP_INIT (write, _IO_default_write),
> JUMP_INIT (seek, _IO_default_seek),
> @@ -361,7 +363,7 @@ const struct _IO_jump_t __io_vtables[] attribute_relro =
> JUMP_INIT (seekpos, _IO_default_seekpos),
> JUMP_INIT (setbuf, _IO_wmem_setbuf),
> JUMP_INIT (sync, _IO_wmem_sync),
> - JUMP_INIT (doallocate, _IO_wdefault_doallocate),
> + JUMP_INIT (doallocate, _IO_wmem_doallocate),
> JUMP_INIT (read, _IO_default_read),
> JUMP_INIT (write, _IO_default_write),
> JUMP_INIT (seek, _IO_default_seek),
> diff --git a/libio/wmemstream.c b/libio/wmemstream.c
> index 168232314a..c449e482c8 100644
> --- a/libio/wmemstream.c
> +++ b/libio/wmemstream.c
> @@ -127,3 +127,13 @@ _IO_wmem_setbuf (FILE *fp, char *p, ssize_t len)
> (void) len;
> return fp;
> }
> +
> +
> +int
> +_IO_wmem_doallocate (FILE *fp)
> +{
> + /* Wmemstreams manage a growable buffer internally. The doallocate
> + hook must not replace it with a generic stdio buffer. */
> + (void) fp;
Ditto.
> + return 1;
> +}
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