Sandra Loosemore <san...@codesourcery.com> writes:
> This patch is for PR 79193 and 88999, problems where libstdc++ is
> mis-configuring itself when building for a bare-metal target because it
> thinks it can link programs without pulling in the BSP that provides
> low-level I/O support. (Specifically, this was observed on nios2-elf
> with Newlib and GDB semihosting.) It'll build just fine if it
> recognizes that it can only compile programs and not link them, but it's
> confused because using an empty program to test for ability to link
> succeeds.
>
> Is this configure change OK, and suitable for stage 4?
>
> BTW, I did run autoconf in every subdirectory that contains a
> configure.ac, but it appears only libstc++-v3 actually uses this test;
> all the other regenerated configure scripts were unchanged.
LGTM FWIW. AIUI the effect will be to use the hard-coded list of
supported newlib features (as intended) instead of trying to detech them
at configure time. But I guess there's a risk that this could unmask
latent problems on other targets by enabling features that some BSPs don't
support, either due to a limited libgloss or due to some other restriction.
Jeff's autotesters will probably pick that up though.
Thanks,
Richard
>
> -Sandra
>
> From 44b769a9b5e01a58c9b89b24ca5a00fc1ff53012 Mon Sep 17 00:00:00 2001
> From: Sandra Loosemore <san...@codesourcery.com>
> Date: Wed, 5 Feb 2020 10:03:58 -0800
> Subject: [PATCH] Use a non-empty test program to test ability to link.
>
> On bare-metal targets, I/O support is typically provided by a BSP and
> requires a linker script and/or hosting library to be specified on the
> linker command line. Linking an empty program with the default linker
> script may succeed, however, which confuses libstdc++ configuration
> when programs that probe for the presence of various I/O features fail
> with link errors.
>
> 2020-02-05 Sandra Loosemore <san...@codesourcery.com>
>
> PR libstdc++/79193
> PR libstdc++/88999
>
> config/
> * no-executables.m4: Use a non-empty program to test for linker
> support.
>
> libstdc++v-3/
> * configure: Regenerated.
> ---
> config/ChangeLog | 8 ++++++++
> config/no-executables.m4 | 4 +++-
> libstdc++-v3/ChangeLog | 7 +++++++
> libstdc++-v3/configure | 4 ++--
> 4 files changed, 20 insertions(+), 3 deletions(-)
>
> diff --git a/config/ChangeLog b/config/ChangeLog
> index f1fec81..d2a12bd 100644
> --- a/config/ChangeLog
> +++ b/config/ChangeLog
> @@ -1,3 +1,11 @@
> +2020-02-05 Sandra Loosemore <san...@codesourcery.com>
> +
> + PR libstdc++/79193
> + PR libstdc++/88999
> +
> + * no-executables.m4: Use a non-empty program to test for linker
> + support.
> +
> 2020-02-01 Andrew Burgess <andrew.burg...@embecosm.com>
>
> * lib-link.m4 (AC_LIB_LINKFLAGS_BODY): Update shell syntax.
> diff --git a/config/no-executables.m4 b/config/no-executables.m4
> index 9061624..6842f84 100644
> --- a/config/no-executables.m4
> +++ b/config/no-executables.m4
> @@ -25,7 +25,9 @@ AC_BEFORE([$0], [_AC_COMPILER_EXEEXT])
> AC_BEFORE([$0], [AC_LINK_IFELSE])
>
> m4_define([_AC_COMPILER_EXEEXT],
> -[AC_LANG_CONFTEST([AC_LANG_PROGRAM()])
> +[AC_LANG_CONFTEST([AC_LANG_PROGRAM(
> + [#include <stdio.h>],
> + [printf ("hello world\n");])])
> # FIXME: Cleanup?
> AS_IF([AC_TRY_EVAL(ac_link)], [gcc_no_link=no], [gcc_no_link=yes])
> if test x$gcc_no_link = xyes; then
> diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
> index 76a6e2b..46ab7c0 100644
> --- a/libstdc++-v3/ChangeLog
> +++ b/libstdc++-v3/ChangeLog
> @@ -1,3 +1,10 @@
> +2020-02-05 Sandra Loosemore <san...@codesourcery.com>
> +
> + PR libstdc++/79193
> + PR libstdc++/88999
> +
> + * configure: Regenerated.
> +
> 2020-02-05 Jonathan Wakely <jwak...@redhat.com>
>
> * include/bits/iterator_concepts.h (iter_reference_t)
> diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
> index a39c33b..9f9c5a2 100755
> --- a/libstdc++-v3/configure
> +++ b/libstdc++-v3/configure
> @@ -4130,11 +4130,11 @@ done
>
> cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> /* end confdefs.h. */
> -
> +#include <stdio.h>
> int
> main ()
> {
> -
> +printf ("hello world\n");
> ;
> return 0;
> }
