[PATCH] libstdc++: Fix up bits/std.cc symlink installation

[Jakub Jelinek]

On Wed, Jun 24, 2026 at 06:56:57AM -0300, Alexandre Oliva wrote:
> 
> libstdc++-v3 in gcc-15 gained uses of a make function that was added
> in GNU make 3.81, but ppc-vx6 is GNU make 3.80, so calling the
> function returns an empty string, and the build fails.
> 
> gcc/doc/install.texi states GCC requires make 3.80 to build, so
> rewrite those bits to avoid the new function.
> 
> Install locations don't need abspath because they're already supposed
> to be absolute, since installation can't work with relative paths and
> DESTDIR is supposed to be prependable.
> 
> $? may gain the srcdir VPATH, which would complicate dropping abspath,
> so iterate over the two filenames.
> 
> Regstrapped on x86_64-linux-gnu.  Also tested with ppc-vx6's make for
> i686-linux-gnu with gcc-15.  Ok to install?
> 
> 
> for  libstdc++-v3/ChangeLog
> 
> 	* src/c++23/Makefile.am (libstdc++.modules.json): Rewrite
> 	without abspath make function.
> 	(stamp-modules-bits): Likewise.
> 	* src/c++23/Makefile.in: Rebuilt.

This change broke various module tests (and got backported even to 15 :( ).
I'm using objdir as a subdirectory of the gcc tree, so ../configure ...

> @@ -57,7 +57,9 @@ std.compat.cc: std.compat.cc.in std-clib.cc.in
>  # Also put the interface units in the build-includes bits directory.
>  stamp-modules-bits: $(includebits_DATA)
>  	@-mkdir -p $(top_builddir)/include/bits
> -	-cd $(top_builddir)/include/bits && $(LN_S) $(abspath $?) . 2>/dev/null
> +	-for f in $(includebits_DATA); do \
> +	  $(LN_S) $(abs_srcdir)/$$f $(top_builddir)/include/bits; \
> +	done 2>/dev/null
>  	@$(STAMP) $@
>  
>  all-local: stamp-module-manifest stamp-modules-bits

Before this change, the
/home/jakub/src/gcc/obj38/x86_64-pc-linux-gnu/libstdc++-v3/include/bits
std.cc symlink used to point to
/home/jakub/src/gcc/obj38/x86_64-pc-linux-gnu/libstdc++-v3/src/c++23/std.cc
Now it points to
/home/jakub/src/gcc/obj40/x86_64-pc-linux-g~-v3/../../../libstdc++-v3/src/c++23/std.cc
which doesn't exist, the source directory only has std.cc.in file from which
the std.cc file is generated in the build directory.

The following patch fixes it by using abs_builddir instead of abs_srcdir.

Fixes up
-FAIL: g++.dg/modules/compile-std1.C -std=c++29 (test for excess errors)
-FAIL: g++.dg/modules/compile-std1.C -std=c++29 module-cmi std (gcm.cache/std.gcm)
-FAIL: g++.dg/modules/compile-std1.C -std=c++29 module-cmi std.compat (gcm.cache/std.compat.gcm)
-FAIL: g++.dg/plugin/std-module-exports-c++20.C -fplugin=./std_module_exports_plugin.so (test for excess errors)
-FAIL: g++.dg/plugin/std-module-exports-c++23.C -fplugin=./std_module_exports_plugin.so (test for excess errors)
-FAIL: g++.dg/plugin/std-module-exports-c++26.C -fplugin=./std_module_exports_plugin.so (test for excess errors)

Ok for trunk/release branches?

2026-06-25  Jakub Jelinek  <jakub@redhat.com>

	* src/c++23/Makefile.am (stamp-modules-bits): Use abs_builddir instead
	of abs_srcdir.
	* src/c++23/Makefile.in: Regenerate.

--- libstdc++-v3/src/c++23/Makefile.am.jj	2026-06-25 00:10:29.319324548 +0200
+++ libstdc++-v3/src/c++23/Makefile.am	2026-06-25 09:09:35.276266154 +0200
@@ -58,7 +58,7 @@ std.compat.cc: std.compat.cc.in std-clib
 stamp-modules-bits: $(includebits_DATA)
 	@-mkdir -p $(top_builddir)/include/bits
 	-for f in $(includebits_DATA); do \
-	  $(LN_S) $(abs_srcdir)/$$f $(top_builddir)/include/bits; \
+	  $(LN_S) $(abs_builddir)/$$f $(top_builddir)/include/bits; \
 	done 2>/dev/null
 	@$(STAMP) $@
 
--- libstdc++-v3/src/c++23/Makefile.in.jj	2026-06-25 00:10:29.319324548 +0200
+++ libstdc++-v3/src/c++23/Makefile.in	2026-06-25 09:09:59.614642142 +0200
@@ -866,7 +866,7 @@ std.compat.cc: std.compat.cc.in std-clib
 stamp-modules-bits: $(includebits_DATA)
 	@-mkdir -p $(top_builddir)/include/bits
 	-for f in $(includebits_DATA); do \
-	  $(LN_S) $(abs_srcdir)/$$f $(top_builddir)/include/bits; \
+	  $(LN_S) $(abs_builddir)/$$f $(top_builddir)/include/bits; \
 	done 2>/dev/null
 	@$(STAMP) $@
 

	Jakub