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Fix fflush handling for mmap files after ungetc (bug 32535)

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As discussed in bug 32535, fflush fails on files opened for reading
using mmap after ungetc.  Fix the logic to handle this case and still
compute the file offset correctly.

Tested for x86_64.
This commit is contained in:
Joseph Myers 2025-01-28 23:20:08 +00:00
parent 0dcc0b2f63
commit 3ff3b9997c
3 changed files with 59 additions and 4 deletions
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12
libio/fileops.c
View File

@ -859,17 +859,21 @@ libc_hidden_ver (_IO_new_file_sync, _IO_file_sync)
int
_IO_file_sync_mmap (FILE *fp)
{
off64_t o = fp->_offset - (fp->_IO_read_end - fp->_IO_read_ptr);
if (fp->_IO_read_ptr != fp->_IO_read_end)
{
if (__lseek64 (fp->_fileno, fp->_IO_read_ptr - fp->_IO_buf_base,
SEEK_SET)
!= fp->_IO_read_ptr - fp->_IO_buf_base)
if (_IO_in_backup (fp))
{
_IO_switch_to_main_get_area (fp);
o -= fp->_IO_read_end - fp->_IO_read_base;
}
if (__lseek64 (fp->_fileno, o, SEEK_SET) != o)
{
fp->_flags |= _IO_ERR_SEEN;
return EOF;
}
}
fp->_offset = fp->_IO_read_ptr - fp->_IO_buf_base;
fp->_offset = o;
fp->_IO_read_end = fp->_IO_read_ptr = fp->_IO_read_base;
return 0;
}

1
stdio-common/Makefile
View File

@ -239,6 +239,7 @@ tests := \
tst-fdopen2 \
tst-ferror \
tst-fflush-all-input \
tst-fflush-mmap \
tst-fgets \
tst-fgets2 \
tst-fileno \

50
stdio-common/tst-fflush-mmap.c Normal file
View File

@ -0,0 +1,50 @@
/* Test fflush after ungetc on files using mmap (bug 32535).
Copyright (C) 2025 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 <stdio.h>
#include <support/check.h>
#include <support/temp_file.h>
#include <support/xstdio.h>
#include <support/xunistd.h>
int
do_test (void)
{
char *filename = NULL;
int fd = create_temp_file ("tst-fflush-mmap", &filename);
TEST_VERIFY_EXIT (fd != -1);
xclose (fd);
/* Test fflush after ungetc (bug 32535). */
FILE *fp = xfopen (filename, "w");
TEST_VERIFY (0 <= fputs ("test", fp));
xfclose (fp);
fp = xfopen (filename, "rm");
TEST_COMPARE (fgetc (fp), 't');
TEST_COMPARE (ungetc ('u', fp), 'u');
TEST_COMPARE (fflush (fp), 0);
TEST_COMPARE (fgetc (fp), 't');
TEST_COMPARE (fgetc (fp), 'e');
xfclose (fp);
return 0;
}
#include <support/test-driver.c>