On Wed, Jan 7, 2026 at 12:52 PM Jonathan Wakely <[email protected]> wrote:
> As explained in the PR, flockfile and funlockfile are always declared by
newlib and there's no easy way to detect whether they're actually
> defined. Ensure that ac_stdio_locking=no gets set for non-cygwin newlib
> targets.
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/123406
> * acinclude.m4 (GLIBCXX_CHECK_STDIO_LOCKING): Override detection
> of flockfile for non-cygwin newlib targets.
> * configure: Regenerate.
> ---
>
> Tested x86_64-linux, where this doesn't change the generated c++config.h
> file.
>
LGTM. Thanks for fixing it.
>
> Built on cris-elf to verify that the _GLIBCXX_USE_STDIO_LOCKING macro is
> no longer defined in c++config.h.
>
> libstdc++-v3/acinclude.m4 | 9 ++++++++-
> libstdc++-v3/configure | 7 +++++++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
> index 103515c000f4..e6723edf880e 100644
> --- a/libstdc++-v3/acinclude.m4
> +++ b/libstdc++-v3/acinclude.m4
> @@ -5822,13 +5822,20 @@ AC_LANG_SAVE
> AC_MSG_CHECKING([whether flockfile and putc_unlocked are defined in
> <stdio.h>])
> AC_TRY_COMPILE([
> #include <stdio.h>
> + #if __has_include(<newlib.h>)
> + # ifdef __CYGWIN__
> + // Cygwin has working flockfile
> + # else
> + # error No usable flockfile on most newlib targets
> + # endif
> + #endif
> ],[
> FILE* f = ::fopen("", "");
> ::flockfile(f);
> ::putc_unlocked(' ', f);
> ::funlockfile(f);
> ::fclose(f);
> - ], [ac_stdio_locking=yes], [ac_stdio_locking=no])
> + ],[ac_stdio_locking=yes],[ac_stdio_locking=no])
> AC_MSG_RESULT($ac_stdio_locking)
>
> if test "$ac_stdio_locking" = yes; then
> diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
> index 0469cbe0f59c..3d825a69fa2e 100755
> --- a/libstdc++-v3/configure
> +++ b/libstdc++-v3/configure
> @@ -55051,6 +55051,13 @@ $as_echo_n "checking whether flockfile and
> putc_unlocked are defined in <stdio.h
> /* end confdefs.h. */
>
> #include <stdio.h>
> + #if __has_include(<newlib.h>)
> + # ifdef __CYGWIN__
> + // Cygwin has working flockfile
> + # else
> + # error No usable flockfile on most newlib targets
> + # endif
> + #endif
>
> int
> main ()
> --
> 2.52.0
>
>
