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libio: Ignore doallocate for open_memstream and open_wmemstream [BZ #34019]

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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>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
This commit is contained in:
Xiang Gao
2026-05-20 17:22:19 -03:00
committed by Adhemerval Zanella
parent b1ab27286e
commit 97bd3b3d56
7 changed files with 107 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files
libio/Makefile
+2
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@@ -120,6 +120,7 @@ tests = \
tst-fwrite-error \
tst-getdelim \
tst-memstream-setbuf \
tst-memstream-setvbuf-doallocate \
tst-memstream1 \
tst-memstream2 \
tst-memstream3 \
@@ -144,6 +145,7 @@ tests = \
tst-wfiledoallocate-static \
tst-widetext \
tst-wmemstream-setbuf \
tst-wmemstream-setvbuf-doallocate \
tst-wmemstream1 \
tst-wmemstream2 \
tst-wmemstream3 \
libio/libioP.h
+2
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@@ -743,10 +743,12 @@ 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_;
libio/memstream.c
+9
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@@ -120,3 +120,12 @@ _IO_mem_setbuf (FILE *fp, char *p, ssize_t len)
/* Memstream manage a growable buffer internally. */
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. */
return 1;
}
libio/tst-memstream-setvbuf-doallocate.c
+61
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@@ -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:
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>
libio/tst-wmemstream-setvbuf-doallocate.c
+20
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@@ -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>
libio/vtables.c
+4 -2
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@@ -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),
libio/wmemstream.c
+9
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@@ -125,3 +125,12 @@ _IO_wmem_setbuf (FILE *fp, char *p, ssize_t len)
/* Wmemstreams manage a growable buffer internally. */
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. */
return 1;
}