On Thu, 20 Oct 2022 at 16:53, Arsen Arsenović via Libstdc++
<libstd...@gcc.gnu.org> wrote:
>
> This enables us to provide symbols for placeholders and numeric limits,
I'm not convinced this is worth doing.
The placeholders and the numeric_limits members are all inline
variables for C++17 and later, and C++17 is the compiler's default
mode. The placeholders aren't even required to exist for freestanding
prior to C++23. For the numeric_limits definitions, I suppose it is a
problem that users can't take their address in freestanding today
unless they compile as C++17.
> and allows users to mess about with linker flags less.
i.e. they don't have to use -nostdlib and/or link with gcc -lsupc++,
but can just use g++?
That seems more compelling than providing definitions of the
placeholders and limits members.
>
> libstdc++-v3/ChangeLog:
>
> * Makefile.am [!_GLIBCXX_HOSTED]: Enable src/ subdirectory.
> * Makefile.in: Regenerate.
> * src/Makefile.am [!_GLIBCXX_HOSTED]: Omit compatibility files.
> There's no history to be compatible with.
> * src/c++11/Makefile.am [!_GLIBCXX_HOSTED]: Omit hosted-only
> source files from the build.
> * src/c++17/Makefile.am [!_GLIBCXX_HOSTED]: Likewise.
> * src/c++20/Makefile.am [!_GLIBCXX_HOSTED]: Likewise.
> * src/c++98/Makefile.am [!_GLIBCXX_HOSTED]: Likewise.
> * src/Makefile.in: Regenerate.
> * src/c++11/Makefile.in: Regenerate.
> * src/c++17/Makefile.in: Regenerate.
> * src/c++20/Makefile.in: Regenerate.
> * src/c++98/Makefile.in: Regenerate.
> ---
> Afternoon,
>
> With these changes, when we aren't hosted, we get a libstdc++ library that
> contains only library facilities available in freestanding (i.e. placeholders
> and limits.cc). This is, AFAICT, the only code in libstdc++.{a,so} that can
> (and should) be available in freestanding.
>
> As an implementation note, this could be a little bit faster (at
> build/configure time), though not necessarily nicer, by having
> src/Makefile.am not try to build convenience libraries for versions of
> C++ that provide nothing. I opted not to do this since it'd make
> src/Makefile.am even more complex, and make future changes harder to
> implement.
> libstdc++ also isn't that slow to build, anyway.
>
> Tested on i686-elf.
>
> Have a good day!
>
> libstdc++-v3/Makefile.am | 4 ++--
> libstdc++-v3/Makefile.in | 4 ++--
> libstdc++-v3/src/Makefile.am | 6 +++++
> libstdc++-v3/src/Makefile.in | 8 +++++--
> libstdc++-v3/src/c++11/Makefile.am | 16 ++++++++++---
> libstdc++-v3/src/c++11/Makefile.in | 37 +++++++++++++++++++-----------
> libstdc++-v3/src/c++17/Makefile.am | 4 ++++
> libstdc++-v3/src/c++17/Makefile.in | 6 +++--
> libstdc++-v3/src/c++20/Makefile.am | 4 ++++
> libstdc++-v3/src/c++20/Makefile.in | 6 +++--
> libstdc++-v3/src/c++98/Makefile.am | 4 ++++
> libstdc++-v3/src/c++98/Makefile.in | 6 +++--
> 12 files changed, 77 insertions(+), 28 deletions(-)
>
> diff --git a/libstdc++-v3/Makefile.am b/libstdc++-v3/Makefile.am
> index 0d147ad3ffe..d7f2b6e76a5 100644
> --- a/libstdc++-v3/Makefile.am
> +++ b/libstdc++-v3/Makefile.am
> @@ -24,11 +24,11 @@ include $(top_srcdir)/fragment.am
>
> if GLIBCXX_HOSTED
> ## Note that python must come after src.
> - hosted_source = src doc po testsuite python
> + hosted_source = doc po testsuite python
> endif
>
> ## Keep this list sync'd with acinclude.m4:GLIBCXX_CONFIGURE.
> -SUBDIRS = include libsupc++ $(hosted_source)
> +SUBDIRS = include libsupc++ src $(hosted_source)
>
> ACLOCAL_AMFLAGS = -I . -I .. -I ../config
>
> diff --git a/libstdc++-v3/src/Makefile.am b/libstdc++-v3/src/Makefile.am
> index b83c222d51d..4eb78e76297 100644
> --- a/libstdc++-v3/src/Makefile.am
> +++ b/libstdc++-v3/src/Makefile.am
> @@ -121,7 +121,13 @@ cxx11_sources = \
> ${cxx0x_compat_sources} \
> ${ldbl_alt128_compat_sources}
>
> +if GLIBCXX_HOSTED
> libstdc___la_SOURCES = $(cxx98_sources) $(cxx11_sources)
> +else
> +# When freestanding, there's currently no compatibility to preserve. Should
> +# that change, any compatibility sources can be added here.
> +libstdc___la_SOURCES =
> +endif
>
> libstdc___la_LIBADD = \
> $(GLIBCXX_LIBS) \
> diff --git a/libstdc++-v3/src/c++11/Makefile.am
> b/libstdc++-v3/src/c++11/Makefile.am
> index ecd46aafc01..72f05100c98 100644
> --- a/libstdc++-v3/src/c++11/Makefile.am
> +++ b/libstdc++-v3/src/c++11/Makefile.am
> @@ -51,6 +51,10 @@ else
> cxx11_abi_sources =
> endif
>
> +sources_freestanding = \
> + limits.cc \
> + placeholders.cc
> +
> sources = \
> chrono.cc \
> codecvt.cc \
> @@ -66,9 +70,7 @@ sources = \
> hashtable_c++0x.cc \
> ios.cc \
> ios_errcat.cc \
> - limits.cc \
> mutex.cc \
> - placeholders.cc \
> random.cc \
> regex.cc \
> shared_ptr.cc \
> @@ -118,7 +120,15 @@ endif
>
> vpath % $(top_srcdir)/src/c++11
>
> -libc__11convenience_la_SOURCES = $(sources) $(inst_sources)
> +if !GLIBCXX_HOSTED
> +libc__11convenience_la_SOURCES = $(sources_freestanding)
> +else
> +libc__11convenience_la_SOURCES = \
> + $(sources_freestanding) \
> + $(sources) \
> + $(inst_sources)
> +endif
> +
>
> # Use special rules for the hashtable.cc file so that all
> # the generated template functions are also instantiated.
> diff --git a/libstdc++-v3/src/c++17/Makefile.am
> b/libstdc++-v3/src/c++17/Makefile.am
> index 3d53f652fac..72095f5b087 100644
> --- a/libstdc++-v3/src/c++17/Makefile.am
> +++ b/libstdc++-v3/src/c++17/Makefile.am
> @@ -60,7 +60,11 @@ sources = \
>
> vpath % $(top_srcdir)/src/c++17
>
> +if GLIBCXX_HOSTED
> libc__17convenience_la_SOURCES = $(sources) $(inst_sources)
> +else
> +libc__17convenience_la_SOURCES =
> +endif
>
> if GLIBCXX_LDBL_ALT128_COMPAT
> floating_from_chars.lo: floating_from_chars.cc
> diff --git a/libstdc++-v3/src/c++20/Makefile.am
> b/libstdc++-v3/src/c++20/Makefile.am
> index d4c1e26e40e..5c937f7e804 100644
> --- a/libstdc++-v3/src/c++20/Makefile.am
> +++ b/libstdc++-v3/src/c++20/Makefile.am
> @@ -40,7 +40,11 @@ sources =
>
> vpath % $(top_srcdir)/src/c++20
>
> +if GLIBCXX_HOSTED
> libc__20convenience_la_SOURCES = $(sources) $(inst_sources)
> +else
> +libc__20convenience_la_SOURCES =
> +endif
>
> # AM_CXXFLAGS needs to be in each subdirectory so that it can be
> # modified in a per-library or per-sub-library way. Need to manually
> diff --git a/libstdc++-v3/src/c++98/Makefile.am
> b/libstdc++-v3/src/c++98/Makefile.am
> index b96588bd95c..f7134d80027 100644
> --- a/libstdc++-v3/src/c++98/Makefile.am
> +++ b/libstdc++-v3/src/c++98/Makefile.am
> @@ -148,7 +148,11 @@ sources = \
>
> vpath % $(top_srcdir)/src/c++98
>
> +if GLIBCXX_HOSTED
> libc__98convenience_la_SOURCES = $(sources)
> +else
> +libc__98convenience_la_SOURCES =
> +endif
>
> # Use special rules to compile with -fimplicit-templates.
> c++locale.lo: c++locale.cc
> # Use special rules for the deprecated source files so that they find
> --
> 2.38.1
>
