diff --git a/pkgs/build-support/cc-wrapper/default.nix b/pkgs/build-support/cc-wrapper/default.nix
index eecaacbd6fea..ad4adaee5e29 100644
--- a/pkgs/build-support/cc-wrapper/default.nix
+++ b/pkgs/build-support/cc-wrapper/default.nix
@@ -728,12 +728,7 @@ stdenvNoCC.mkDerivation {
     ''
     # GCC NG friendly libc++
     + optionalString (libcxx != null && libcxx.isGNU or false) ''
-      for dir in ${getDev libcxx}/include/c++/*; do
-        echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
-      done
-      for dir in ${getDev libcxx}/include/c++/*/${targetPlatform.config}; do
-        echo "-isystem $dir" >> $out/nix-support/libcxx-cxxflags
-      done
+      echo "-isystem ${getDev libcxx}/include" >> $out/nix-support/libcxx-cxxflags
     ''
 
     ##
diff --git a/pkgs/development/compilers/gcc/ng/15/gcc/custom-threading-model.patch b/pkgs/development/compilers/gcc/ng/15/gcc/custom-threading-model.patch
deleted file mode 100644
index fb82e194263f..000000000000
--- a/pkgs/development/compilers/gcc/ng/15/gcc/custom-threading-model.patch
+++ /dev/null
@@ -1,162 +0,0 @@
-From 46280d27a5c96b2efa7a61f49ee8dc14f7e10d0c Mon Sep 17 00:00:00 2001
-From: John Ericson <git@JohnEricson.me>
-Date: Sun, 22 Aug 2021 01:14:22 -0400
-Subject: [PATCH] Factor out thread model detection with `GCC_AC_THREAD_MODEL`
-MIME-Version: 1.0
-Content-Type: text/plain; charset=UTF-8
-Content-Transfer-Encoding: 8bit
-
-This macro deduplicates the
-
-    $CC -v 2>&1 | sed -n 's/^Thread model: //p'
-
-check that was occurring in various runtime libs.
-
-Additionally, as a bit of an Easter egg, this also allows overriding
-what the compiler would return by setting the
-`gcc_cv_target_thread_file` cache variable first. I admit that it is in
-fact this Easter egg that led me to write the patch. The use-case for it
-is for making multilib builds where the library sets do not all share
-the same thread model easier. See also `THREAD_MODEL_SPEC` for more
-about the varying thread models use-case.
-
-Arguably one could could try to define on `THREAD_MODEL_SPEC` on more
-platforms (besides e.g. AIX) but the ramifications of this are a bit
-unclear. Setting `gcc_cv_target_thread_file` directly is a "low tech"
-solution that will work for now for sure. Of course, since setting a
-cache variable like this a hacky trick, I will not expect this to be at
-all stable/guaranteed to work, going forward.
-
-Thanks to Arsen who on IRC discussed these things with me, including in
-particular making it a cache var not `--with-model` flag, to not
-prematurely foster expectations that this is stable.
-
-Suggested-by: Arsen Arsenović <arsen@aarsen.me>
----
- config/gthr.m4              | 23 +++++++++++++++++++++++
- libatomic/configure.ac      |  4 +---
- libgcc/configure.ac         |  4 +---
- libphobos/m4/druntime/os.m4 |  2 +-
- libstdc++-v3/acinclude.m4   |  8 +++-----
- 5 files changed, 29 insertions(+), 12 deletions(-)
-
-diff --git a/config/gthr.m4 b/config/gthr.m4
-index 11996247f15..e8fac4a5721 100644
---- a/config/gthr.m4
-+++ b/config/gthr.m4
-@@ -5,6 +5,26 @@ dnl Public License, this file may be distributed as part of a program
- dnl that contains a configuration script generated by Autoconf, under
- dnl the same distribution terms as the rest of that program.
- 
-+dnl Define thread model
-+
-+dnl usage: GCC_AC_THREAD_MODEL
-+AC_DEFUN([GCC_AC_THREAD_MODEL],
-+[
-+# Specify the threading model for this GCC runtime library
-+# Pass with no value to take from compiler's metadata
-+# Pass with a value to specify a thread package
-+# 'single' means single threaded -- without threads.
-+AC_CACHE_CHECK([for the threading model used by GCC], [gcc_cv_target_thread_file], [
-+  # Set new cache variable
-+  gcc_cv_target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'`
-+])
-+# Set variable name (not prefixed enough to be a good cache variable
-+# name) traditionally used for this purpose, to avoid having to change
-+# a bunch of configure scripts.
-+target_thread_file="$gcc_cv_target_thread_file"
-+])
-+
-+
- dnl Define header location by thread model
- 
- dnl usage: GCC_AC_THREAD_HEADER([thread_model])
-@@ -23,6 +43,9 @@ case $1 in
-     vxworks)	thread_header=config/gthr-vxworks.h ;;
-     win32)	thread_header=config/i386/gthr-win32.h ;;
-     mcf)	thread_header=config/i386/gthr-mcf.h ;;
-+    *)
-+        AC_MSG_ERROR([No known header for threading model '$1'.])
-+        ;;
- esac
- AC_SUBST(thread_header)
- ])
-diff --git a/libatomic/configure.ac b/libatomic/configure.ac
-index aafae71028d..a1aa3bdf69f 100644
---- a/libatomic/configure.ac
-+++ b/libatomic/configure.ac
-@@ -162,9 +162,7 @@ libtool_VERSION=3:0:2
- AC_SUBST(libtool_VERSION)
- 
- # Check for used threading-model
--AC_MSG_CHECKING([for thread model used by GCC])
--target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'`
--AC_MSG_RESULT([$target_thread_file])
-+GCC_AC_THREAD_MODEL
- 
- case "$target" in
-  *aarch64*)
-diff --git a/libgcc/configure.ac b/libgcc/configure.ac
-index 85e4f1bc48b..d44493f9653 100644
---- a/libgcc/configure.ac
-+++ b/libgcc/configure.ac
-@@ -305,9 +305,7 @@ AC_SUBST([use_tm_clone_registry])
- 
- AC_LIB_PROG_LD_GNU
- 
--AC_MSG_CHECKING([for thread model used by GCC])
--target_thread_file=`$CC -v 2>&1 | sed -n 's/^Thread model: //p'`
--AC_MSG_RESULT([$target_thread_file]) 
-+GCC_AC_THREAD_MODEL
- 
- # Check for assembler CFI support.
- AC_CACHE_CHECK([whether assembler supports CFI directives], [libgcc_cv_cfi],
-diff --git a/libphobos/m4/druntime/os.m4 b/libphobos/m4/druntime/os.m4
-index ef8ca434407..7bb91362dbe 100644
---- a/libphobos/m4/druntime/os.m4
-+++ b/libphobos/m4/druntime/os.m4
-@@ -32,7 +32,7 @@ case $1 in
-     # TODO: These targets need porting.
-     dce|mipssde|rtems|tpf|vxworks)
- 	    DCFG_THREAD_MODEL="Single" ;;
--    *)	    as_fn_error "Thread implementation '$1' not recognised" "$LINENO" 5 ;;
-+    *)	    AC_MSG_ERROR([Thread implementation '$1' not recognised]) ;;
- esac
- AC_SUBST(DCFG_THREAD_MODEL)
- ])
-diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
-index a0094c2dd95..66fc3abe4fd 100644
---- a/libstdc++-v3/acinclude.m4
-+++ b/libstdc++-v3/acinclude.m4
-@@ -4345,9 +4345,7 @@ dnl Substs:
- dnl  thread_header
- dnl
- AC_DEFUN([GLIBCXX_ENABLE_THREADS], [
--  AC_MSG_CHECKING([for thread model used by GCC])
--  target_thread_file=`$CXX -v 2>&1 | sed -n 's/^Thread model: //p'`
--  AC_MSG_RESULT([$target_thread_file])
-+  GCC_AC_THREAD_MODEL
-   GCC_AC_THREAD_HEADER([$target_thread_file])
- ])
- 
-@@ -4357,7 +4355,8 @@ dnl Check if gthread implementation defines the types and functions
- dnl required by the c++0x thread library.  Conforming gthread
- dnl implementations can define __GTHREADS_CXX0X to enable use with c++0x.
- dnl
--dnl GLIBCXX_ENABLE_SYMVERS must be done before this.
-+dnl GLIBCXX_ENABLE_SYMVERS and GLIBCXX_ENABLE_THREADS must be done
-+dnl before this.
- dnl
- AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [
-   GLIBCXX_ENABLE(libstdcxx-threads,auto,,[enable C++11 threads support])
-@@ -4372,7 +4371,6 @@ AC_DEFUN([GLIBCXX_CHECK_GTHREADS], [
-   CXXFLAGS="$CXXFLAGS -fno-exceptions \
- 	-I${toplevel_srcdir}/libgcc -I${toplevel_builddir}/libgcc"
- 
--  target_thread_file=`$CXX -v 2>&1 | sed -n 's/^Thread model: //p'`
-   case $target_thread_file in
-     posix)
-       CXXFLAGS="$CXXFLAGS -DSUPPORTS_WEAK -DGTHREAD_USE_WEAK -D_PTHREADS"
--- 
-2.47.2
-
diff --git a/pkgs/development/compilers/gcc/ng/15/libgcc/force-regular-dirs.patch b/pkgs/development/compilers/gcc/ng/15/libgcc/force-regular-dirs.patch
new file mode 100644
index 000000000000..c67f2f4498ea
--- /dev/null
+++ b/pkgs/development/compilers/gcc/ng/15/libgcc/force-regular-dirs.patch
@@ -0,0 +1,49 @@
+From bb3277895d3bd77bcacb7c489ebb1390478bbc12 Mon Sep 17 00:00:00 2001
+From: John Ericson <John.Ericson@Obsidian.Systems>
+Date: Thu, 17 Jul 2025 11:00:07 -0400
+Subject: [PATCH 2/2] Force regular dirs
+
+Override directories in libgcc so they are normal $out/lib and
+$dev/include. This is not suitable for upstreaming, but is done on top
+of a different patch which is, and which makes this smaller.
+
+---
+ libgcc/Makefile.in  | 6 +++---
+ libgcc/configure.ac | 3 ---
+ 2 files changed, 3 insertions(+), 6 deletions(-)
+
+diff --git a/libgcc/Makefile.in b/libgcc/Makefile.in
+index 4661c36703d..986cd035148 100644
+--- a/libgcc/Makefile.in
++++ b/libgcc/Makefile.in
+@@ -202,10 +202,10 @@ STRIP = @STRIP@
+ STRIP_FOR_TARGET = $(STRIP)
+ 
+ # Used to install the shared libgcc.
+-slibdir = @slibdir@
++slibdir = $(libdir)
+ # Maybe used for DLLs on Windows targets.
+-toolexecdir = @toolexecdir@
+-toolexeclibdir = @toolexeclibdir@
++toolexecdir = $(bindir)
++toolexeclibdir = $(libdir)
+ 
+ export AR_FOR_TARGET
+ export AR_CREATE_FOR_TARGET
+diff --git a/libgcc/configure.ac b/libgcc/configure.ac
+index 5fdac5d95f2..89044cb65c9 100644
+--- a/libgcc/configure.ac
++++ b/libgcc/configure.ac
+@@ -479,9 +479,6 @@ if test x"$enable_as_accelerator_for" != x; then
+   accel_dir_suffix=/accel/${target_noncanonical}
+   real_host_noncanonical=${enable_as_accelerator_for}
+ fi
+-# Directory in which the compiler finds libraries etc.
+-libdir=${orig_libdir}/gcc/${real_host_noncanonical}/'$(version)'${accel_dir_suffix}
+-includedir=${libdir}/include
+ 
+ if test x"$enable_offload_targets" != x; then
+   extra_parts="${extra_parts} crtoffloadbegin.o crtoffloadend.o"
+-- 
+2.47.2
+
diff --git a/pkgs/development/compilers/gcc/ng/15/libgfortran/force-regular-dirs.patch b/pkgs/development/compilers/gcc/ng/15/libgfortran/force-regular-dirs.patch
new file mode 100644
index 000000000000..fc7b69ea6e6e
--- /dev/null
+++ b/pkgs/development/compilers/gcc/ng/15/libgfortran/force-regular-dirs.patch
@@ -0,0 +1,53 @@
+From 7a0c8ca8872a73c6886940448ba9b3203b13268d Mon Sep 17 00:00:00 2001
+From: John Ericson <git@JohnEricson.me>
+Date: Mon, 21 Jul 2025 11:42:13 -0400
+Subject: [PATCH] libgfortran: Force regular include/lib dir
+
+---
+ libgfortran/Makefile.am | 13 +++++--------
+ 1 file changed, 5 insertions(+), 8 deletions(-)
+
+diff --git a/libgfortran/Makefile.am b/libgfortran/Makefile.am
+index 21b35c76a06..3d38cde5b42 100644
+--- a/libgfortran/Makefile.am
++++ b/libgfortran/Makefile.am
+@@ -42,14 +42,13 @@ extra_darwin_ldflags_libgfortran += -Wc,-nodefaultrpaths
+ extra_darwin_ldflags_libgfortran += -Wl,-rpath,@loader_path
+ endif
+ 
+-gfor_c_HEADERS = ISO_Fortran_binding.h
+-gfor_cdir = $(libdir)/gcc/$(target_alias)/$(gcc_version)/include
++include_HEADERS = ISO_Fortran_binding.h
+ 
+ LTLDFLAGS = $(shell $(SHELL) $(top_srcdir)/../libtool-ldflags $(LDFLAGS)) \
+ 	    $(lt_host_flags)
+ 
+-toolexeclib_LTLIBRARIES = libgfortran.la
+-toolexeclib_DATA = libgfortran.spec
++lib_LTLIBRARIES = libgfortran.la
++toolexeclib_DATA = libgfortran.spec # needs "exec" in name
+ libgfortran_la_LINK = $(LINK) $(libgfortran_la_LDFLAGS)
+ libgfortran_la_LDFLAGS = -version-info `grep -v '^\#' $(srcdir)/libtool-version` \
+ 	$(LTLDFLAGS) $(LIBQUADLIB) ../libbacktrace/libbacktrace.la \
+@@ -58,16 +57,14 @@ libgfortran_la_LDFLAGS = -version-info `grep -v '^\#' $(srcdir)/libtool-version`
+ 	$(version_arg) -Wc,-shared-libgcc
+ libgfortran_la_DEPENDENCIES = $(version_dep) libgfortran.spec $(LIBQUADLIB_DEP)
+ 
+-cafexeclib_LTLIBRARIES = libcaf_single.la
+-cafexeclibdir = $(libdir)/gcc/$(target_alias)/$(gcc_version)$(MULTISUBDIR)
++lib_LTLIBRARIES += libcaf_single.la
+ libcaf_single_la_SOURCES = caf/single.c
+ libcaf_single_la_LDFLAGS = -static
+ libcaf_single_la_DEPENDENCIES = caf/libcaf.h
+ libcaf_single_la_LINK = $(LINK) $(libcaf_single_la_LDFLAGS)
+ 
+ if IEEE_SUPPORT
+-fincludedir = $(libdir)/gcc/$(target_alias)/$(gcc_version)$(MULTISUBDIR)/finclude
+-nodist_finclude_HEADERS = ieee_arithmetic.mod ieee_exceptions.mod ieee_features.mod
++nodist_include_HEADERS = ieee_arithmetic.mod ieee_exceptions.mod ieee_features.mod
+ endif
+ 
+ ## io.h conflicts with a system header on some platforms, so
+-- 
+2.47.2
+
diff --git a/pkgs/development/compilers/gcc/ng/15/libssp/force-regular-dirs.patch b/pkgs/development/compilers/gcc/ng/15/libssp/force-regular-dirs.patch
new file mode 100644
index 000000000000..4b15c9a1d8b0
--- /dev/null
+++ b/pkgs/development/compilers/gcc/ng/15/libssp/force-regular-dirs.patch
@@ -0,0 +1,30 @@
+From e7dac0e90f3e4363d858a6f147d7cc4f62815dd6 Mon Sep 17 00:00:00 2001
+From: John Ericson <John.Ericson@Obsidian.Systems>
+Date: Fri, 18 Jul 2025 16:54:17 -0400
+Subject: [PATCH 3/3] Force regular dirs
+
+Override directories in libssp so they are normal $out/lib and
+$dev/include. This is not suitable for upstreaming, but is done on top
+of a different patch which is, and which makes this smaller.
+---
+ libssp/configure.ac | 4 ----
+ 1 file changed, 4 deletions(-)
+
+diff --git a/libssp/configure.ac b/libssp/configure.ac
+index 5b9fa4fbecc..f1723dc33ce 100644
+--- a/libssp/configure.ac
++++ b/libssp/configure.ac
+@@ -207,10 +207,6 @@ esac
+ AC_SUBST(toolexecdir)
+ AC_SUBST(toolexeclibdir)
+ 
+-# Directory in which the compiler finds libraries etc.
+-libdir='$(toolexeclibdir)'
+-includedir=${orig_libdir}/gcc/${host_noncanonical}/'$(version)/include'
+-
+ if test ${multilib} = yes; then
+   multilib_arg="--enable-multilib"
+ else
+-- 
+2.47.2
+
diff --git a/pkgs/development/compilers/gcc/ng/15/libstdcxx/force-regular-dirs.patch b/pkgs/development/compilers/gcc/ng/15/libstdcxx/force-regular-dirs.patch
new file mode 100644
index 000000000000..e80cffdce1e7
--- /dev/null
+++ b/pkgs/development/compilers/gcc/ng/15/libstdcxx/force-regular-dirs.patch
@@ -0,0 +1,120 @@
+From db427c55334dd2edc11397d3a92d55dc9c06d1c3 Mon Sep 17 00:00:00 2001
+From: John Ericson <git@JohnEricson.me>
+Date: Sun, 20 Jul 2025 14:20:00 -0400
+Subject: [PATCH] libstdc++: Force regular include/lib dir
+
+Delete a bunch of unneeded logic to do this.
+---
+ libstdc++-v3/acinclude.m4        | 80 ++------------------------------
+ libstdc++-v3/include/Makefile.am |  2 +-
+ 2 files changed, 4 insertions(+), 78 deletions(-)
+
+diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
+index a0094c2dd95..a0718dff394 100644
+--- a/libstdc++-v3/acinclude.m4
++++ b/libstdc++-v3/acinclude.m4
+@@ -727,85 +727,11 @@ dnl
+ dnl This logic must match gcc/configure.ac's setting of gcc_gxx_include_dir.
+ dnl config/gxx-include-dir.m4 must be kept consistant with this as well.
+ AC_DEFUN([GLIBCXX_EXPORT_INSTALL_INFO], [
+-  glibcxx_toolexecdir=no
+-  glibcxx_toolexeclibdir=no
++  glibcxx_toolexecdir='$(libdir)'
++  glibcxx_toolexeclibdir='$(libdir)'
++  gxx_include_dir='$(includedir)'
+   glibcxx_prefixdir=$prefix
+ 
+-  AC_MSG_CHECKING([for gxx-include-dir])
+-  AC_ARG_WITH([gxx-include-dir],
+-    AC_HELP_STRING([--with-gxx-include-dir=DIR],
+-		   [installation directory for include files]),
+-    [case "$withval" in
+-      yes) AC_MSG_ERROR([Missing directory for --with-gxx-include-dir]) ;;
+-      no)  gxx_include_dir=no ;;
+-      *)   gxx_include_dir=$withval ;;
+-     esac],
+-    [gxx_include_dir=no])
+-  AC_MSG_RESULT($gxx_include_dir)
+-
+-  AC_MSG_CHECKING([for --enable-version-specific-runtime-libs])
+-  AC_ARG_ENABLE([version-specific-runtime-libs],
+-    AC_HELP_STRING([--enable-version-specific-runtime-libs],
+-		   [Specify that runtime libraries should be installed in a compiler-specific directory]),
+-    [case "$enableval" in
+-      yes) version_specific_libs=yes ;;
+-      no)  version_specific_libs=no ;;
+-      *)   AC_MSG_ERROR([Unknown argument to enable/disable version-specific libs]);;
+-     esac],
+-    [version_specific_libs=no])
+-  AC_MSG_RESULT($version_specific_libs)
+-
+-  GCC_WITH_TOOLEXECLIBDIR
+-
+-  # Default case for install directory for include files.
+-  if test $version_specific_libs = no && test $gxx_include_dir = no; then
+-    gxx_include_dir='include/c++/${gcc_version}'
+-    if test -n "$with_cross_host" &&
+-       test x"$with_cross_host" != x"no"; then
+-      gxx_include_dir='${prefix}/${target_alias}/'"$gxx_include_dir"
+-    else
+-      gxx_include_dir='${prefix}/'"$gxx_include_dir"
+-    fi
+-  fi
+-
+-  # Version-specific runtime libs processing.
+-  if test $version_specific_libs = yes; then
+-    # Need the gcc compiler version to know where to install libraries
+-    # and header files if --enable-version-specific-runtime-libs option
+-    # is selected.  FIXME: these variables are misnamed, there are
+-    # no executables installed in _toolexecdir or _toolexeclibdir.
+-    if test x"$gxx_include_dir" = x"no"; then
+-      gxx_include_dir='${libdir}/gcc/${host_alias}/${gcc_version}/include/c++'
+-    fi
+-    glibcxx_toolexecdir='${libdir}/gcc/${host_alias}'
+-    glibcxx_toolexeclibdir='${toolexecdir}/${gcc_version}$(MULTISUBDIR)'
+-  fi
+-
+-  # Calculate glibcxx_toolexecdir, glibcxx_toolexeclibdir
+-  # Install a library built with a cross compiler in tooldir, not libdir.
+-  if test x"$glibcxx_toolexecdir" = x"no"; then
+-    if test -n "$with_cross_host" &&
+-       test x"$with_cross_host" != x"no"; then
+-      glibcxx_toolexecdir='${exec_prefix}/${host_alias}'
+-      case ${with_toolexeclibdir} in
+-	no)
+-	  glibcxx_toolexeclibdir='${toolexecdir}/lib'
+-	  ;;
+-	*)
+-	  glibcxx_toolexeclibdir=${with_toolexeclibdir}
+-	  ;;
+-      esac
+-    else
+-      glibcxx_toolexecdir='${libdir}/gcc/${host_alias}'
+-      glibcxx_toolexeclibdir='${libdir}'
+-    fi
+-    multi_os_directory=`$CXX -print-multi-os-directory`
+-    case $multi_os_directory in
+-      .) ;; # Avoid trailing /.
+-      *) glibcxx_toolexeclibdir=$glibcxx_toolexeclibdir/$multi_os_directory ;;
+-    esac
+-  fi
+-
+   AC_MSG_CHECKING([for install location])
+   AC_MSG_RESULT($gxx_include_dir)
+ 
+diff --git a/libstdc++-v3/include/Makefile.am b/libstdc++-v3/include/Makefile.am
+index 537774c2668..c0bfeb43b44 100644
+--- a/libstdc++-v3/include/Makefile.am
++++ b/libstdc++-v3/include/Makefile.am
+@@ -1048,7 +1048,7 @@ endif
+ 
+ host_srcdir = ${glibcxx_srcdir}/$(OS_INC_SRCDIR)
+ host_builddir = ./${host_alias}/bits
+-host_installdir = ${gxx_include_dir}/${host_alias}$(MULTISUBDIR)/bits
++host_installdir = ${gxx_include_dir}/bits
+ host_headers = \
+ 	${host_srcdir}/ctype_base.h \
+ 	${host_srcdir}/ctype_inline.h \
+-- 
+2.47.2
+
diff --git a/pkgs/development/compilers/gcc/ng/common/libatomic/default.nix b/pkgs/development/compilers/gcc/ng/common/libatomic/default.nix
index ab5632313b76..49fef931007a 100644
--- a/pkgs/development/compilers/gcc/ng/common/libatomic/default.nix
+++ b/pkgs/development/compilers/gcc/ng/common/libatomic/default.nix
@@ -5,35 +5,81 @@
   release_version,
   version,
   getVersionFile,
-  autoreconfHook269,
   monorepoSrc ? null,
+  fetchpatch,
+  autoreconfHook269,
   runCommand,
 }:
 stdenv.mkDerivation (finalAttrs: {
   pname = "libatomic";
   inherit version;
 
-  src = monorepoSrc;
+  src = runCommand "libatomic-src-${version}" { src = monorepoSrc; } ''
+    runPhase unpackPhase
+
+    mkdir -p "$out/gcc"
+    cp gcc/BASE-VER "$out/gcc"
+    cp gcc/DATESTAMP "$out/gcc"
+
+    cp -r libatomic "$out"
+
+    cp -r config "$out"
+    cp -r multilib.am "$out"
+    cp -r libtool.m4 "$out"
+
+    cp config.guess "$out"
+    cp config.rpath "$out"
+    cp config.sub "$out"
+    cp config-ml.in "$out"
+    cp ltmain.sh "$out"
+    cp install-sh "$out"
+    cp mkinstalldirs "$out"
+
+    [[ -f MD5SUMS ]]; cp MD5SUMS "$out"
+  '';
 
   patches = [
-    (getVersionFile "gcc/custom-threading-model.patch")
+    (fetchpatch {
+      name = "custom-threading-model.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250716204545.1063669-1-git@JohnEricson.me/raw";
+      hash = "sha256-kxNntY2r4i/+XHQSpf9bYV2Jg+FD/pD5TiMn5hd4ckk=";
+      includes = [
+        "config/*"
+        "libatomic/*"
+      ];
+    })
   ];
 
+  postUnpack = ''
+    mkdir -p ./build
+    buildRoot=$(readlink -e "./build")
+  '';
+
+  preAutoreconf = ''
+    sourceRoot=$(readlink -e "./libatomic")
+    cd $sourceRoot
+  '';
+
   enableParallelBuilding = true;
 
   nativeBuildInputs = [
     autoreconfHook269
   ];
 
-  postPatch = ''
-    sourceRoot=$(readlink -e "./libatomic")
-  '';
+  configurePlatforms = [
+    "build"
+    "host"
+  ];
+
+  configureFlags = [
+    "--disable-dependency-tracking"
+    "cross_compiling=true"
+    "--disable-multilib"
+  ];
 
   preConfigure = ''
-    mkdir ../build
-    cd ../build
+    cd "$buildRoot"
     configureScript=$sourceRoot/configure
-    chmod +x "$configureScript"
   '';
 
   doCheck = true;
diff --git a/pkgs/development/compilers/gcc/ng/common/libgcc/default.nix b/pkgs/development/compilers/gcc/ng/common/libgcc/default.nix
index 907534c8f6f8..a1372a69e123 100644
--- a/pkgs/development/compilers/gcc/ng/common/libgcc/default.nix
+++ b/pkgs/development/compilers/gcc/ng/common/libgcc/default.nix
@@ -6,6 +6,7 @@
   version,
   getVersionFile,
   monorepoSrc ? null,
+  fetchpatch,
   autoreconfHook269,
   buildGccPackages,
   buildPackages,
@@ -37,7 +38,32 @@ stdenv.mkDerivation (finalAttrs: {
   ];
 
   patches = [
-    (getVersionFile "gcc/custom-threading-model.patch")
+    (fetchpatch {
+      name = "delete-MACHMODE_H.patch";
+      url = "https://github.com/gcc-mirror/gcc/commit/493aae4b034d62054d5e7e54dc06cd9a8be54e29.diff";
+      hash = "sha256-oEk0lnI96RlpALWpb7J+GnrtgQsFVqDO57I/zjiqqTk=";
+    })
+    (fetchpatch {
+      name = "custom-threading-model.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250716204545.1063669-1-git@JohnEricson.me/raw";
+      hash = "sha256-NgiC4cFeFInXXg27me1XpSeImPaL0WHs50Tf1YHz4ps=";
+    })
+    (fetchpatch {
+      name = "libgcc.mvars-less-0.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250716234028.1153560-1-John.Ericson@Obsidian.Systems/raw";
+      hash = "sha256-NEcieDCsy+7IRU3qQKVD3i57OuwGZKB/rmNF8X2I1n0=";
+    })
+    (fetchpatch {
+      name = "libgcc.mvars-less-1.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250716234028.1153560-2-John.Ericson@Obsidian.Systems/raw";
+      hash = "sha256-nfRC4f6m3kHDro4+6E4y1ZPs+prxBQmn0H2rzIjaMWM=";
+    })
+    (fetchpatch {
+      name = "regular-libdir-includedir.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250717174911.1536129-1-git@JohnEricson.me/raw";
+      hash = "sha256-Cn7rvg1FI7H/26GzSe4pv5VW/gvwbwGqivAqEeawkwk=";
+    })
+    (getVersionFile "libgcc/force-regular-dirs.patch")
   ];
 
   autoreconfFlags = "--install --force --verbose . libgcc";
@@ -95,7 +121,6 @@ stdenv.mkDerivation (finalAttrs: {
         tm.h \
         options.h \
         insn-constants.h \
-        insn-modes.h \
         version.h
       )
       mkdir -p "$buildRoot/gcc/include"
@@ -186,11 +211,7 @@ stdenv.mkDerivation (finalAttrs: {
   makeFlags = [ "MULTIBUILDTOP:=../" ];
 
   postInstall = ''
-    cp gthr-default.h "$out/lib/gcc/${stdenv.hostPlatform.config}/${version}/include"
-    moveToOutput "lib/gcc/${stdenv.hostPlatform.config}/${version}/include" "$dev"
-    mkdir -p "$out/lib" "$dev/include"
-    ln -s "$out/lib/gcc/${stdenv.hostPlatform.config}/${version}"/* "$out/lib"
-    ln -s "$dev/lib/gcc/${stdenv.hostPlatform.config}/${version}/include"/* "$dev/include/"
+    install -c -m 644 gthr-default.h "$dev/include"
   '';
 
   doCheck = true;
diff --git a/pkgs/development/compilers/gcc/ng/common/libgfortran/default.nix b/pkgs/development/compilers/gcc/ng/common/libgfortran/default.nix
index 7e2c5bc4fcd7..5b77efbb4ce2 100644
--- a/pkgs/development/compilers/gcc/ng/common/libgfortran/default.nix
+++ b/pkgs/development/compilers/gcc/ng/common/libgfortran/default.nix
@@ -5,10 +5,11 @@
   gcc_meta,
   release_version,
   version,
+  getVersionFile,
   monorepoSrc ? null,
-  buildPackages,
   autoreconfHook269,
   libiberty,
+  buildPackages,
   libgcc,
   libbacktrace,
 }:
@@ -32,6 +33,10 @@ stdenv.mkDerivation (finalAttrs: {
     gfortran
   ];
 
+  patches = [
+    (getVersionFile "libgfortran/force-regular-dirs.patch")
+  ];
+
   autoreconfFlags = "--install --force --verbose . libgfortran";
 
   postUnpack = ''
@@ -161,6 +166,7 @@ stdenv.mkDerivation (finalAttrs: {
     "gcc_cv_target_thread_file=single"
     # $CC cannot link binaries, let alone run then
     "cross_compiling=true"
+    "--with-toolexeclibdir=${builtins.placeholder "dev"}/lib"
   ];
 
   # Set the variable back the way it was, see corresponding code in
@@ -171,13 +177,6 @@ stdenv.mkDerivation (finalAttrs: {
 
   makeFlags = [ "MULTIBUILDTOP:=../" ];
 
-  postInstall = ''
-    moveToOutput "lib/gcc/${stdenv.hostPlatform.config}/${version}/include" "$dev"
-    mkdir -p "$out/lib" "$dev/include"
-    ln -s "$out/lib/gcc/${stdenv.hostPlatform.config}/${version}"/* "$out/lib"
-    ln -s "$dev/lib/gcc/${stdenv.hostPlatform.config}/${version}/include"/* "$dev/include/"
-  '';
-
   doCheck = true;
 
   passthru = {
diff --git a/pkgs/development/compilers/gcc/ng/common/libssp/default.nix b/pkgs/development/compilers/gcc/ng/common/libssp/default.nix
index 3c4cc19582c5..bcc5d4b9c2e3 100644
--- a/pkgs/development/compilers/gcc/ng/common/libssp/default.nix
+++ b/pkgs/development/compilers/gcc/ng/common/libssp/default.nix
@@ -4,7 +4,10 @@
   gcc_meta,
   release_version,
   version,
+  getVersionFile,
   monorepoSrc ? null,
+  fetchpatch,
+  autoreconfHook269,
   runCommand,
 }:
 stdenv.mkDerivation (finalAttrs: {
@@ -20,6 +23,9 @@ stdenv.mkDerivation (finalAttrs: {
 
     cp -r libssp "$out"
 
+    cp -r config "$out"
+    cp -r multilib.am "$out"
+
     cp config.guess "$out"
     cp config.rpath "$out"
     cp config.sub "$out"
@@ -31,23 +37,50 @@ stdenv.mkDerivation (finalAttrs: {
     [[ -f MD5SUMS ]]; cp MD5SUMS "$out"
   '';
 
-  sourceRoot = "${finalAttrs.src.name}/libssp";
+  outputs = [
+    "out"
+    "dev"
+  ];
+
+  patches = [
+    (fetchpatch {
+      name = "regular-libdir-includedir.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250720172933.2404828-1-git@JohnEricson.me/raw";
+      hash = "sha256-W7dcy1Tm3O2reK7kx83DRv8W97qUfaqDbKLiLXIegRw=";
+    })
+    (getVersionFile "libssp/force-regular-dirs.patch")
+  ];
+
+  postUnpack = ''
+    mkdir -p ./build
+    buildRoot=$(readlink -e "./build")
+  '';
+
+  preAutoreconf = ''
+    sourceRoot=$(readlink -e "./libssp")
+    cd $sourceRoot
+  '';
+
+  enableParallelBuilding = true;
+
+  nativeBuildInputs = [
+    autoreconfHook269
+  ];
 
   configurePlatforms = [
     "build"
     "host"
   ];
+
   configureFlags = [
     "--disable-dependency-tracking"
-    "--with-toolexeclibdir=${builtins.placeholder "out" + "/lib"}"
     "cross_compiling=true"
     "--disable-multilib"
   ];
 
   preConfigure = ''
-    mkdir ../../build
-    cd ../../build
-    configureScript=../$sourceRoot/configure
+    cd "$buildRoot"
+    configureScript=$sourceRoot/configure
   '';
 
   hardeningDisable = [
diff --git a/pkgs/development/compilers/gcc/ng/common/libstdcxx/default.nix b/pkgs/development/compilers/gcc/ng/common/libstdcxx/default.nix
index c8fbc047c515..c7108fced4f4 100644
--- a/pkgs/development/compilers/gcc/ng/common/libstdcxx/default.nix
+++ b/pkgs/development/compilers/gcc/ng/common/libstdcxx/default.nix
@@ -6,25 +6,62 @@
   version,
   getVersionFile,
   monorepoSrc ? null,
-  runCommand,
+  fetchpatch,
   autoreconfHook269,
+  runCommand,
   gettext,
 }:
 stdenv.mkDerivation (finalAttrs: {
   pname = "libstdcxx";
   inherit version;
 
-  src = monorepoSrc;
+  src = runCommand "libstdcxx-src-${version}" { src = monorepoSrc; } ''
+    runPhase unpackPhase
 
-  enableParallelBuilding = true;
+    mkdir -p "$out/gcc"
+    cp gcc/BASE-VER "$out/gcc"
+    cp gcc/DATESTAMP "$out/gcc"
 
-  nativeBuildInputs = [
-    autoreconfHook269
-    gettext
+    mkdir -p "$out/libgcc"
+    cp libgcc/gthr*.h "$out/libgcc"
+    cp libgcc/unwind-pe.h "$out/libgcc"
+
+    cp -r libstdc++-v3 "$out"
+
+    cp -r libiberty "$out"
+    cp -r include "$out"
+    cp -r contrib "$out"
+
+    cp -r config "$out"
+    cp -r multilib.am "$out"
+
+    cp config.guess "$out"
+    cp config.rpath "$out"
+    cp config.sub "$out"
+    cp config-ml.in "$out"
+    cp ltmain.sh "$out"
+    cp install-sh "$out"
+    cp mkinstalldirs "$out"
+
+    [[ -f MD5SUMS ]]; cp MD5SUMS "$out"
+  '';
+
+  outputs = [
+    "out"
+    "dev"
   ];
 
   patches = [
-    (getVersionFile "gcc/custom-threading-model.patch")
+    (fetchpatch {
+      name = "custom-threading-model.patch";
+      url = "https://inbox.sourceware.org/gcc-patches/20250716204545.1063669-1-git@JohnEricson.me/raw";
+      hash = "sha256-jPP0+MoPLtCwWcW6doO6KHCppwAYK40qNVyriLXcGOg=";
+      includes = [
+        "config/*"
+        "libstdc++-v3/*"
+      ];
+    })
+    (getVersionFile "libstdcxx/force-regular-dirs.patch")
   ];
 
   postUnpack = ''
@@ -37,12 +74,12 @@ stdenv.mkDerivation (finalAttrs: {
     cd $sourceRoot
   '';
 
-  postPatch = ''
-    sed -i \
-      -e 's/AM_ENABLE_MULTILIB(/AM_ENABLE_MULTILIB(NOPE/' \
-      -e 's#glibcxx_toolexeclibdir=no#glibcxx_toolexeclibdir=${builtins.placeholder "out"}/libexec#' \
-      configure.ac
-  '';
+  enableParallelBuilding = true;
+
+  nativeBuildInputs = [
+    autoreconfHook269
+    gettext
+  ];
 
   preConfigure = ''
     cd "$buildRoot"
@@ -50,9 +87,13 @@ stdenv.mkDerivation (finalAttrs: {
     chmod +x "$configureScript"
   '';
 
+  configurePlatforms = [
+    "build"
+    "host"
+  ];
+
   configureFlags = [
     "--disable-dependency-tracking"
-    "--with-toolexeclibdir=${builtins.placeholder "out"}/lib"
     "gcc_cv_target_thread_file=posix"
     "cross_compiling=true"
     "--disable-multilib"
@@ -64,16 +105,15 @@ stdenv.mkDerivation (finalAttrs: {
     "--with-default-libstdcxx-abi=new"
   ];
 
-  outputs = [
-    "out"
-    "dev"
-  ];
-
   hardeningDisable = [
     # PATH_MAX
     "fortify"
   ];
 
+  postInstall = ''
+    moveToOutput lib/libstdc++.modules.json "$dev"
+  '';
+
   doCheck = true;
 
   passthru = {
diff --git a/pkgs/development/compilers/gcc/ng/common/patches.nix b/pkgs/development/compilers/gcc/ng/common/patches.nix
index d69ec0098fab..81d3be9f68bf 100644
--- a/pkgs/development/compilers/gcc/ng/common/patches.nix
+++ b/pkgs/development/compilers/gcc/ng/common/patches.nix
@@ -32,9 +32,29 @@
     }
   ];
 
-  # Submitted: https://gcc.gnu.org/pipermail/gcc-patches/2025-July/689429.html
-  # In Git: https://github.com/Ericson2314/gcc/tree/libgcc-custom-threading-model-15
-  "gcc/custom-threading-model.patch" = [
+  # In Git: https://github.com/Ericson2314/gcc/tree/regular-dirs-in-libgcc-15
+  "libgcc/force-regular-dirs.patch" = [
+    {
+      after = "15";
+      path = ../15;
+    }
+  ];
+  # In Git: https://github.com/Ericson2314/gcc/tree/regular-dirs-in-libssp-15
+  "libssp/force-regular-dirs.patch" = [
+    {
+      after = "15";
+      path = ../15;
+    }
+  ];
+  # In Git: https://github.com/Ericson2314/gcc/tree/libstdcxx-force-regular-dirs-15
+  "libstdcxx/force-regular-dirs.patch" = [
+    {
+      after = "15";
+      path = ../15;
+    }
+  ];
+  # In Git: https://github.com/Ericson2314/gcc/tree/libgfortran-force-regular-dirs-15
+  "libgfortran/force-regular-dirs.patch" = [
     {
       after = "15";
       path = ../15;