C2x scanf binary constant handling

C2x adds binary integer constants starting with 0b or 0B, and supports
those constants for the %i scanf format (in addition to the %b format,
which isn't yet implemented for scanf in glibc).  Implement that scanf
support for glibc.

As with the strtol support, this is incompatible with previous C
standard versions, in that such an input string starting with 0b or 0B
was previously required to be parsed as 0 (with the rest of the input
potentially matching subsequent parts of the scanf format string).
Thus this patch adds 12 new __isoc23_* functions per long double
format (12, 24 or 36 depending on how many long double formats the
glibc configuration supports), with appropriate header redirection
support (generally very closely following that for the __isoc99_*
scanf functions - note that __GLIBC_USE (DEPRECATED_SCANF) takes
precedence over __GLIBC_USE (C2X_STRTOL), so the case of GNU
extensions to C89 continues to get old-style GNU %a and does not get
this new feature).  The function names would remain as __isoc23_* even
if C2x ends up published in 2024 rather than 2023.

When scanf %b support is added, I think it will be appropriate for all
versions of scanf to follow C2x rules for inputs to the %b format
(given that there are no compatibility concerns for a new format).

Tested for x86_64 (full glibc testsuite).  The first version was also
tested for powerpc (32-bit) and powerpc64le (stdio-common/ and wcsmbs/
tests), and with build-many-glibcs.py.

14 files changed, 530 insertions, 0 deletions

diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 92a3499a94..a14ee487ea 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -47,6 +47,12 @@ routines := \
   isoc99_vfscanf \
   isoc99_vscanf \
   isoc99_vsscanf \
+  isoc23_fscanf \
+  isoc23_scanf \
+  isoc23_sscanf \
+  isoc23_vfscanf \
+  isoc23_vscanf \
+  isoc23_vsscanf \
   itoa-digits \
   itoa-udigits \
   itowa-digits \
@@ -214,6 +220,10 @@ tests := \
   tst-put-error \
   tst-renameat2 \
   tst-rndseek \
+  tst-scanf-binary-c11 \
+  tst-scanf-binary-c2x \
+  tst-scanf-binary-gnu11 \
+  tst-scanf-binary-gnu89 \
   tst-scanf-round \
   tst-setvbuf1 \
   tst-sprintf \
@@ -415,6 +425,10 @@ CFLAGS-isoc99_vfscanf.c += -fexceptions
 CFLAGS-isoc99_vscanf.c += -fexceptions
 CFLAGS-isoc99_fscanf.c += -fexceptions
 CFLAGS-isoc99_scanf.c += -fexceptions
+CFLAGS-isoc23_vfscanf.c += -fexceptions
+CFLAGS-isoc23_vscanf.c += -fexceptions
+CFLAGS-isoc23_fscanf.c += -fexceptions
+CFLAGS-isoc23_scanf.c += -fexceptions
 
 CFLAGS-dprintf.c += $(config-cflags-wno-ignored-attributes)
 
@@ -440,6 +454,14 @@ CFLAGS-tst-bz11319-fortify2.c += -D_FORTIFY_SOURCE=2
 
 CFLAGS-tst-memstream-string.c += -fno-builtin-fprintf
 
+# Some versions of GCC supported for building glibc do not support -std=c2x, so
+# the test for that version uses -std=c11 and then _ISOC2X_SOURCE is defined in
+# the test as needed.
+CFLAGS-tst-scanf-binary-c11.c += -std=c11 -DOBJPFX=\"$(objpfx)\"
+CFLAGS-tst-scanf-binary-c2x.c += -std=c11 -DOBJPFX=\"$(objpfx)\"
+CFLAGS-tst-scanf-binary-gnu11.c += -std=gnu11 -DOBJPFX=\"$(objpfx)\"
+CFLAGS-tst-scanf-binary-gnu89.c += -std=gnu89 -DOBJPFX=\"$(objpfx)\"
+
 CPPFLAGS += $(libio-mtsafe)
 
 $(objpfx)tst-setvbuf1.out: /dev/null $(objpfx)tst-setvbuf1
diff --git a/stdio-common/Versions b/stdio-common/Versions
index 522f302198..4bcfc3fb41 100644
--- a/stdio-common/Versions
+++ b/stdio-common/Versions
@@ -63,6 +63,14 @@ libc {
   GLIBC_2.29 {
     # SHLIB_COMPAT(GLIBC_2_0, GLIBC_2_29) used in iovfscanf.c etc.
   }
+  GLIBC_2.38 {
+    __isoc23_scanf;
+    __isoc23_vscanf;
+    __isoc23_fscanf;
+    __isoc23_vfscanf;
+    __isoc23_sscanf;
+    __isoc23_vsscanf;
+  }
   GLIBC_PRIVATE {
     # global variables
     _itoa_lower_digits;
diff --git a/stdio-common/isoc23_fscanf.c b/stdio-common/isoc23_fscanf.c
new file mode 100644
index 0000000000..dc19f57bec
--- /dev/null
+++ b/stdio-common/isoc23_fscanf.c
@@ -0,0 +1,35 @@
+/* Copyright (C) 1991-2023 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 <libioP.h>
+#include <stdarg.h>
+#include <stdio.h>
+
+/* Read formatted input from STREAM according to the format string FORMAT.  */
+int
+__isoc23_fscanf (FILE *stream, const char *format, ...)
+{
+  va_list arg;
+  int done;
+
+  va_start (arg, format);
+  done = __vfscanf_internal (stream, format, arg,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+  va_end (arg);
+
+  return done;
+}
diff --git a/stdio-common/isoc23_scanf.c b/stdio-common/isoc23_scanf.c
new file mode 100644
index 0000000000..22b5aaebda
--- /dev/null
+++ b/stdio-common/isoc23_scanf.c
@@ -0,0 +1,35 @@
+/* Copyright (C) 1991-2023 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 <stdarg.h>
+#include <stdio.h>
+#include <libioP.h>
+
+/* Read formatted input from stdin according to the format string FORMAT.  */
+int
+__isoc23_scanf (const char *format, ...)
+{
+  va_list arg;
+  int done;
+
+  va_start (arg, format);
+  done = __vfscanf_internal (stdin, format, arg,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+  va_end (arg);
+
+  return done;
+}
diff --git a/stdio-common/isoc23_sscanf.c b/stdio-common/isoc23_sscanf.c
new file mode 100644
index 0000000000..1da4c53846
--- /dev/null
+++ b/stdio-common/isoc23_sscanf.c
@@ -0,0 +1,37 @@
+/* Copyright (C) 1991-2023 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 <stdarg.h>
+#include <libio/strfile.h>
+
+/* Read formatted input from S, according to the format string FORMAT.  */
+int
+__isoc23_sscanf (const char *s, const char *format, ...)
+{
+  va_list arg;
+  int done;
+  _IO_strfile sf;
+  FILE *f = _IO_strfile_read (&sf, s);
+
+  va_start (arg, format);
+  done = __vfscanf_internal (f, format, arg,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+  va_end (arg);
+
+  return done;
+}
+libc_hidden_def (__isoc23_sscanf)
diff --git a/stdio-common/isoc23_vfscanf.c b/stdio-common/isoc23_vfscanf.c
new file mode 100644
index 0000000000..d1411a2d65
--- /dev/null
+++ b/stdio-common/isoc23_vfscanf.c
@@ -0,0 +1,28 @@
+/* Copyright (C) 1991-2023 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 <libioP.h>
+#include <stdio.h>
+
+/* Read formatted input from STREAM according to the format string FORMAT.  */
+int
+__isoc23_vfscanf (FILE *stream, const char *format, va_list args)
+{
+  return __vfscanf_internal (stream, format, args,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+}
+libc_hidden_def (__isoc23_vfscanf)
diff --git a/stdio-common/isoc23_vscanf.c b/stdio-common/isoc23_vscanf.c
new file mode 100644
index 0000000000..81be184c3b
--- /dev/null
+++ b/stdio-common/isoc23_vscanf.c
@@ -0,0 +1,27 @@
+/* Copyright (C) 1991-2023 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 <libioP.h>
+#include <stdio.h>
+
+/* Read formatted input from STDIN according to the format string FORMAT.  */
+int
+__isoc23_vscanf (const char *format, va_list args)
+{
+  return __vfscanf_internal (stdin, format, args,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+}
diff --git a/stdio-common/isoc23_vsscanf.c b/stdio-common/isoc23_vsscanf.c
new file mode 100644
index 0000000000..6cc9a89edc
--- /dev/null
+++ b/stdio-common/isoc23_vsscanf.c
@@ -0,0 +1,28 @@
+/* Copyright (C) 1993-2023 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/strfile.h>
+
+int
+__isoc23_vsscanf (const char *string, const char *format, va_list args)
+{
+  _IO_strfile sf;
+  FILE *f = _IO_strfile_read (&sf, string);
+  return __vfscanf_internal (f, format, args,
+			     SCANF_ISOC99_A | SCANF_ISOC23_BIN_CST);
+}
+libc_hidden_def (__isoc23_vsscanf)
diff --git a/stdio-common/tst-scanf-binary-c11.c b/stdio-common/tst-scanf-binary-c11.c
new file mode 100644
index 0000000000..1869bb6881
--- /dev/null
+++ b/stdio-common/tst-scanf-binary-c11.c
@@ -0,0 +1,28 @@
+/* Test scanf functions with C2X binary integers (narrow strings,
+   no extensions to C11).
+   Copyright (C) 2022-2023 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/>.  */
+
+#undef _GNU_SOURCE
+
+#define CHAR char
+#define FNW
+#define L_(C) C
+#define TEST_C2X 0
+#define STD "c11"
+
+#include <tst-scanf-binary-main.c>
diff --git a/stdio-common/tst-scanf-binary-c2x.c b/stdio-common/tst-scanf-binary-c2x.c
new file mode 100644
index 0000000000..6033b1f375
--- /dev/null
+++ b/stdio-common/tst-scanf-binary-c2x.c
@@ -0,0 +1,31 @@
+/* Test scanf functions with C2X binary integers (narrow strings,
+   no extensions).
+   Copyright (C) 2022-2023 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/>.  */
+
+/* Some versions of GCC supported for building glibc do not support
+   -std=c2x.  */
+#undef _GNU_SOURCE
+#define _ISOC2X_SOURCE
+
+#define CHAR char
+#define FNW
+#define L_(C) C
+#define TEST_C2X 1
+#define STD "c2x"
+
+#include <tst-scanf-binary-main.c>
diff --git a/stdio-common/tst-scanf-binary-gnu11.c b/stdio-common/tst-scanf-binary-gnu11.c
new file mode 100644
index 0000000000..4bd49700d7
--- /dev/null
+++ b/stdio-common/tst-scanf-binary-gnu11.c
@@ -0,0 +1,26 @@
+/* Test scanf functions with C2X binary integers (narrow strings,
+   GNU extensions to C11).
+   Copyright (C) 2022-2023 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 CHAR char
+#define FNW
+#define L_(C) C
+#define TEST_C2X 1
+#define STD "gnu11"
+
+#include <tst-scanf-binary-main.c>
diff --git a/stdio-common/tst-scanf-binary-gnu89.c b/stdio-common/tst-scanf-binary-gnu89.c
new file mode 100644
index 0000000000..5325732f7c
--- /dev/null
+++ b/stdio-common/tst-scanf-binary-gnu89.c
@@ -0,0 +1,26 @@
+/* Test scanf functions with C2X binary integers (narrow strings,
+   GNU extensions to C89).
+   Copyright (C) 2022-2023 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 CHAR char
+#define FNW
+#define L_(C) C
+#define TEST_C2X 0
+#define STD "gnu89"
+
+#include <tst-scanf-binary-main.c>
diff --git a/stdio-common/tst-scanf-binary-main.c b/stdio-common/tst-scanf-binary-main.c
new file mode 100644
index 0000000000..6b75cb32e5
--- /dev/null
+++ b/stdio-common/tst-scanf-binary-main.c
@@ -0,0 +1,189 @@
+/* Test scanf functions with C2X binary integers.
+   Copyright (C) 2022-2023 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 <stdarg.h>
+#include <stdio.h>
+#include <wchar.h>
+
+#include <support/check.h>
+#include <support/xstdio.h>
+
+#define CONCAT_(X, Y, Z) X ## Y ## Z
+#define CONCAT(X, Y, Z) CONCAT_ (X, Y, Z)
+#define FNX(FN1, FN2) CONCAT (FN1, FNW, FN2)
+#ifndef STDX
+# define STDX ""
+#endif
+
+#define INFILE OBJPFX "/tst-" STDX "scanf-binary-" STD "-in"
+
+static int
+wrap_vfscanf (FILE *fp, const CHAR *format, ...)
+{
+  va_list ap;
+  va_start (ap, format);
+  int ret = FNX (vf, scanf) (fp, format, ap);
+  va_end (ap);
+  return ret;
+}
+
+static int
+wrap_vscanf (const CHAR *format, ...)
+{
+  va_list ap;
+  va_start (ap, format);
+  int ret = FNX (v, scanf) (format, ap);
+  va_end (ap);
+  return ret;
+}
+
+static int
+wrap_vsscanf (const CHAR *s, const CHAR *format, ...)
+{
+  va_list ap;
+  va_start (ap, format);
+  int ret = FNX (vs, scanf) (s, format, ap);
+  va_end (ap);
+  return ret;
+}
+
+static void
+one_check (const CHAR *s, int expected, char expected_c)
+{
+  int ret;
+  FILE *fp;
+  int ret_i;
+  long int ret_l;
+  long long int ret_ll;
+  char ret_c;
+  fp = xfopen (INFILE, "w");
+  ret = FNX (fput, s) (s, fp);
+  TEST_VERIFY_EXIT (0 <= ret);
+  xfclose (fp);
+
+  if (!TEST_C2X)
+    {
+      expected = 0;
+      expected_c = s[0] == L_('-') ? s[2] : s[1];
+    }
+
+  ret = FNX (s, scanf) (s, L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = FNX (f, scanf) (fp, L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = FNX (, scanf) (L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  ret = wrap_vsscanf (s, L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = wrap_vfscanf (fp, L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = wrap_vscanf (L_("%i %c"), &ret_i, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_i, expected);
+  TEST_COMPARE (ret_c, expected_c);
+
+  ret = FNX (s, scanf) (s, L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = FNX (f, scanf) (fp, L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = FNX (, scanf) (L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  ret = wrap_vsscanf (s, L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = wrap_vfscanf (fp, L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = wrap_vscanf (L_("%li %c"), &ret_l, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_l, expected);
+  TEST_COMPARE (ret_c, expected_c);
+
+  ret = FNX (s, scanf) (s, L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = FNX (f, scanf) (fp, L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = FNX (, scanf) (L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  ret = wrap_vsscanf (s, L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  fp = xfopen (INFILE, "r");
+  ret = wrap_vfscanf (fp, L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+  xfclose (fp);
+  fp = xfreopen (INFILE, "r", stdin);
+  ret = wrap_vscanf (L_("%lli %c"), &ret_ll, &ret_c);
+  TEST_COMPARE (ret, 2);
+  TEST_COMPARE (ret_ll, expected);
+  TEST_COMPARE (ret_c, expected_c);
+}
+
+static int
+do_test (void)
+{
+  one_check (L_("0b101 x"), 5, 'x');
+  one_check (L_("0B101 x"), 5, 'x');
+  one_check (L_("-0b11111 y"), -31, 'y');
+  one_check (L_("-0B11111 y"), -31, 'y');
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/stdio-common/vfscanf-internal.c b/stdio-common/vfscanf-internal.c
index 4fec12345c..d9675bd4b1 100644
--- a/stdio-common/vfscanf-internal.c
+++ b/stdio-common/vfscanf-internal.c
@@ -1428,6 +1428,16 @@ __vfscanf_internal (FILE *s, const char *format, va_list argptr,
 		      c = inchar ();
 		    }
 		}
+	      else if ((mode_flags & SCANF_ISOC23_BIN_CST) != 0
+		       && base == 0
+		       && width != 0
+		       && TOLOWER (c) == L_('b'))
+		{
+		  base = 2;
+		  if (width > 0)
+		    --width;
+		  c = inchar ();
+		}
 	      else if (base == 0)
 		base = 8;
 	    }