Re: [PATCH] LoongArch: Link c++ header directory in the default ABI to the toplevel.

[Xi Ruoyao <xry111@xry111.site>]

On Wed, 2023-09-06 at 18:06 +0800, Yang Yujie wrote:
> When multilib is enabled, the c++ header directory of the default multilib
> variant needs to be linked to the toplevel since g++ does not search the
> toplevel in this case.
> 
> libstdc++-v3/ChangeLog:
> 
>         * configure.host: Register t-loongarch in tmake_file.
>         * config/cpu/loongarch/t-loongarch: New file.  Link c++ header
>         directory in the default ABI to the toplevel.
> ---
>  libstdc++-v3/config/cpu/loongarch/t-loongarch | 12 ++++++++++++
>  libstdc++-v3/configure.host                   |  5 ++++-
>  2 files changed, 16 insertions(+), 1 deletion(-)
>  create mode 100644 libstdc++-v3/config/cpu/loongarch/t-loongarch
> 
> diff --git a/libstdc++-v3/config/cpu/loongarch/t-loongarch
> b/libstdc++-v3/config/cpu/loongarch/t-loongarch
> new file mode 100644
> index 00000000000..942eddeb3be
> --- /dev/null
> +++ b/libstdc++-v3/config/cpu/loongarch/t-loongarch
> @@ -0,0 +1,12 @@
> +LA_DEFAULT_MULTIDIR = $(shell $(CXX) --print-multi-directory)
> +TOPLEV_HEADERS = $(DESTDIR)${gxx_include_dir}/${host_alias}/$(LA_DEFAULT_MULTIDIR)
> +
> +.PHONY: install-toplevel-link
> +install: install-toplevel-link
> +install-toplevel-link:
> +       if test x$(MULTIDO) != xtrue && \
> +          test x$(LA_DEFAULT_MULTIDIR) != x.; then \
> +           $(MKDIR_P) "$(dir $(TOPLEV_HEADERS))"; \
> +           rm -rf "$(TOPLEV_HEADERS)"; \
> +           $(LN_S) ../ "$(TOPLEV_HEADERS)"; \

From autoconf info page:

 -- Macro: AC_PROG_LN_S
     If ‘ln -s’ works on the current file system (the operating system
     and file system support symbolic links), set the output variable
     ‘LN_S’ to ‘ln -s’; otherwise, if ‘ln’ works, set ‘LN_S’ to ‘ln’,
     and otherwise set it to ‘cp -pR’.

     If you make a link in a directory other than the current directory,
     its meaning depends on whether ‘ln’ or ‘ln -s’ is used.  To safely
     create links using ‘$(LN_S)’, either find out which form is used
     and adjust the arguments, or always invoke ‘ln’ in the directory
     where the link is to be created.

     In other words, it does not work to do:
          $(LN_S) foo /x/bar

     Instead, do:

          (cd /x && $(LN_S) foo bar)

But for this special case we cannot "cp -pR ../ $(TOPLEV_HEADERS)"
either:

$ cp ../* -pR something
cp: cannot copy a directory, '../g', into itself, 'h/g'

So I guess we'll need something like

if ln -s ../ "$(TOPLEV_HEADERS)"; then
  # OK!
  true
else
  # system does not support symlink :(
  # install another copy of toplevel headers into default multilib subdir
  TODO: ????????
fi

And all libstdc++ patches should Cc: libstdc++@gcc.gnu.org.

> +       fi
> diff --git a/libstdc++-v3/configure.host b/libstdc++-v3/configure.host
> index 9e7c7f02dfd..9dc42ad3edb 100644
> --- a/libstdc++-v3/configure.host
> +++ b/libstdc++-v3/configure.host
> @@ -315,7 +315,10 @@ esac
>  # Set any OS-dependent and CPU-dependent bits.
>  # THIS TABLE IS SORTED.  KEEP IT THAT WAY.
>  case "${host}" in
> -  *-*-linux* | *-*-uclinux*)
> + loongarch*)
> +    tmake_file="cpu/loongarch/t-loongarch"
> +    ;;
> + *-*-linux* | *-*-uclinux*)
>      case "${host_cpu}" in
>        i[567]86)
>          abi_baseline_pair=i486-linux-gnu

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University