120 lines
4.0 KiB
Diff
120 lines
4.0 KiB
Diff
commit 377e9733b50ce41e496c467ddcc112f73c88f3bd
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Author: Joseph Myers <josmyers@redhat.com>
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Date: Tue Jan 28 19:38:27 2025 +0000
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Fix fflush after ungetc on input file (bug 5994)
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As discussed in bug 5994 (plus duplicates), POSIX requires fflush
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after ungetc to discard pushed-back characters but preserve the file
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position indicator. For this purpose, each ungetc decrements the file
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position indicator by 1; it is unspecified after ungetc at the start
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of the file, and after ungetwc, so no special handling is needed for
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either of those cases.
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This is fixed with appropriate logic in _IO_new_file_sync. I haven't
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made any attempt to test or change things in this area for the "old"
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functions; the case of files using mmap is addressed in a subsequent
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patch (and there seem to be no problems in this area with files opened
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with fmemopen).
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Tested for x86_64.
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diff --git a/libio/fileops.c b/libio/fileops.c
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index d40748e0fc548fff..83fd272c8e606b1b 100644
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--- a/libio/fileops.c
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+++ b/libio/fileops.c
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@@ -799,6 +799,11 @@ _IO_new_file_sync (FILE *fp)
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if (fp->_IO_write_ptr > fp->_IO_write_base)
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if (_IO_do_flush(fp)) return EOF;
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delta = fp->_IO_read_ptr - fp->_IO_read_end;
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+ if (_IO_in_backup (fp))
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+ {
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+ _IO_switch_to_main_get_area (fp);
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+ delta += fp->_IO_read_ptr - fp->_IO_read_end;
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+ }
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if (delta != 0)
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{
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off64_t new_pos = _IO_SYSSEEK (fp, delta, 1);
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diff --git a/stdio-common/Makefile b/stdio-common/Makefile
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index 95fd52fbf1b1b3fb..e155b96309f4486f 100644
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--- a/stdio-common/Makefile
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+++ b/stdio-common/Makefile
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@@ -277,6 +277,7 @@ tests := \
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tst-swscanf \
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tst-tmpnam \
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tst-ungetc \
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+ tst-ungetc-fflush \
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tst-ungetc-leak \
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tst-ungetc-nomem \
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tst-unlockedio \
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diff --git a/stdio-common/tst-ungetc-fflush.c b/stdio-common/tst-ungetc-fflush.c
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new file mode 100644
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index 0000000000000000..a86d1fdb7f8cac88
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--- /dev/null
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+++ b/stdio-common/tst-ungetc-fflush.c
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@@ -0,0 +1,64 @@
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+/* Test flushing input file after ungetc (bug 5994).
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+ Copyright (C) 2025 Free Software Foundation, Inc.
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+ This file is part of the GNU C Library.
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+
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+ The GNU C Library is free software; you can redistribute it and/or
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+ modify it under the terms of the GNU Lesser General Public
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+ License as published by the Free Software Foundation; either
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+ version 2.1 of the License, or (at your option) any later version.
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+
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+ The GNU C Library is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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+ Lesser General Public License for more details.
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+
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+ You should have received a copy of the GNU Lesser General Public
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+ License along with the GNU C Library; if not, see
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+ <https://www.gnu.org/licenses/>. */
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+
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+#include <stdio.h>
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+
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+#include <support/check.h>
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+#include <support/temp_file.h>
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+#include <support/xstdio.h>
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+#include <support/xunistd.h>
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+
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+int
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+do_test (void)
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+{
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+ char *filename = NULL;
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+ int fd = create_temp_file ("tst-ungetc-fflush", &filename);
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+ TEST_VERIFY_EXIT (fd != -1);
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+ xclose (fd);
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+
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+ /* Test as in bug 5994. */
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+ FILE *fp = xfopen (filename, "w");
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+ TEST_VERIFY_EXIT (fputs ("#include", fp) >= 0);
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+ xfclose (fp);
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+ fp = xfopen (filename, "r");
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+ TEST_COMPARE (fgetc (fp), '#');
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+ TEST_COMPARE (fgetc (fp), 'i');
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+ TEST_COMPARE (ungetc ('@', fp), '@');
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+ TEST_COMPARE (fflush (fp), 0);
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+ TEST_COMPARE (lseek (fileno (fp), 0, SEEK_CUR), 1);
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+ TEST_COMPARE (fgetc (fp), 'i');
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+ TEST_COMPARE (fgetc (fp), 'n');
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+ xfclose (fp);
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+
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+ /* Test as in bug 12799 (duplicate of 5994). */
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+ fp = xfopen (filename, "w+");
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+ TEST_VERIFY_EXIT (fputs ("hello world", fp) >= 0);
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+ rewind (fp);
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+ TEST_VERIFY (fileno (fp) >= 0);
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+ char buffer[10];
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+ TEST_COMPARE (fread (buffer, 1, 5, fp), 5);
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+ TEST_COMPARE (fgetc (fp), ' ');
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+ TEST_COMPARE (ungetc ('@', fp), '@');
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+ TEST_COMPARE (fflush (fp), 0);
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+ TEST_COMPARE (fgetc (fp), ' ');
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+ xfclose (fp);
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+
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+ return 0;
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+}
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+
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+#include <support/test-driver.c>
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