libstdc++: Fix --enable-cstdio=stdio_pure [PR110574]

When configured with --enable-cstdio=stdio_pure we need to consistently
use fseek and not mix seeks on the file descriptor with reads and writes
on the FILE stream.

There are also a number of bugs related to error handling and return
values, because fread and fwrite return 0 on error, not -1, and fseek
returns 0 on success, not the file offset.

libstdc++-v3/ChangeLog:

	PR libstdc++/110574
	* acinclude.m4 (GLIBCXX_CHECK_LFS): Check for fseeko and ftello
	and define _GLIBCXX_USE_FSEEKO_FTELLO.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* config/io/basic_file_stdio.cc (xwrite) [_GLIBCXX_USE_STDIO_PURE]:
	Check for fwrite error correctly.
	(__basic_file<char>::xsgetn) [_GLIBCXX_USE_STDIO_PURE]: Check for
	fread error correctly.
	(get_file_offset): New function.
	(__basic_file<char>::seekoff) [_GLIBCXX_USE_STDIO_PURE]: Use
	fseeko if available. Use get_file_offset instead of return value
	of fseek.
	(__basic_file<char>::showmanyc): Use get_file_offset.

1 files changed, 66 insertions, 0 deletions

diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index c8d5508..36f217c 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -19940,6 +19940,72 @@ $as_echo "$glibcxx_cv_LFS" >&6; }
 $as_echo "#define _GLIBCXX_USE_LFS 1" >>confdefs.h
 
   fi
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for fseeko and ftello" >&5
+$as_echo_n "checking for fseeko and ftello... " >&6; }
+if ${glibcxx_cv_posix_lfs+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    if test x$gcc_no_link = xyes; then
+  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <stdio.h>
+
+int
+main ()
+{
+FILE* fp;
+       fseeko(fp, 0, SEEK_CUR);
+       ftello(fp);
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_posix_lfs=yes
+else
+  glibcxx_cv_posix_lfs=no
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+else
+  if test x$gcc_no_link = xyes; then
+  as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
+fi
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <stdio.h>
+
+int
+main ()
+{
+FILE* fp;
+       fseeko(fp, 0, SEEK_CUR);
+       ftello(fp);
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_link "$LINENO"; then :
+  glibcxx_cv_posix_lfs=yes
+else
+  glibcxx_cv_posix_lfs=no
+fi
+rm -f core conftest.err conftest.$ac_objext \
+    conftest$ac_exeext conftest.$ac_ext
+fi
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_posix_lfs" >&5
+$as_echo "$glibcxx_cv_posix_lfs" >&6; }
+  if test $glibcxx_cv_posix_lfs = yes; then
+
+$as_echo "#define _GLIBCXX_USE_FSEEKO_FTELLO 1" >>confdefs.h
+
+  fi
+
   CXXFLAGS="$ac_save_CXXFLAGS"
   ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'