ci: add spack package for a tsan-instrumented libstdc++

- gcc ships no supported switch to build libstdc++ with -fsanitize=thread,
  and spack's gcc recipe filters all flags out of the target-library build
  (CXXFLAGS_FOR_TARGET is owned by its generated --with-build-config=spack
  makefile), so provide a dedicated libstdcxx-tsan package in a custom repo
- build only the libstdc++-v3 subtree from the matching gcc release tarball,
  configured standalone against the already-installed toolchain (recipe
  modeled on https://iree.dev/developers/debugging/sanitizers/), instead of
  rebuilding all of gcc
- the result is a drop-in runtime replacement for the compiler's libstdc++
  (same soname and symbol versions), to be loaded only by the instrumented
  test executables
- normalize the install layout after make install: the standalone build puts
  the runtime libraries into the multilib os dir (lib64 on x86_64) regardless
  of --libdir, and --with-toolexeclibdir only applies to cross builds
- register the repo in the setup-deps action before creating the env

.github/actions/setup-deps/action.yml

@@ -69,6 +69,7 @@ runs:
       shell: spack-bash {0}
       run: |
         echo "::group::Install dependencies"
+        spack repo add "$GITHUB_WORKSPACE/test/ci/spack_repo/fairmq_ci"
         spack env create fairmq test/ci/spack-${{ inputs.env }}.yaml
         spack -e fairmq add gcc@${{ inputs.gcc }}
         spack -e fairmq config add "packages:all:require:'%gcc@${{ inputs.gcc }}'"

test/ci/spack_repo/fairmq_ci/packages/libstdcxx_tsan/package.py

@@ -0,0 +1,90 @@
+import os
+import shutil
+
+from spack_repo.builtin.build_systems.generic import Package
+
+from spack.package import *
+
+
+class LibstdcxxTsan(Package):
+    """ThreadSanitizer-instrumented build of GCC's libstdc++.
+
+    GCC ships no supported way to produce a tsan-instrumented libstdc++ (and
+    spack's gcc package offers no hook into the target-library flags), so this
+    package builds only the libstdc++-v3 subtree from the GCC release tarball
+    matching the toolchain, with -fsanitize=thread. The result is a drop-in
+    runtime replacement for the compiler's own libstdc++ (same soname and
+    symbol versions) that lets tsan observe the synchronization inside the
+    C++ standard library (e.g. std::locale/std::regex lazy initialization).
+
+    Select it via LD_LIBRARY_PATH in the environment of the instrumented
+    executables only. Like any shared library built with gcc
+    -fsanitize=thread it carries unresolved __tsan_* symbols satisfied by the
+    executable's libtsan, so loading it into an uninstrumented executable
+    fails.
+
+    Recipe modeled on https://iree.dev/developers/debugging/sanitizers/.
+    """
+
+    homepage = "https://gcc.gnu.org/onlinedocs/libstdc++/"
+    url = "https://ftp.gnu.org/gnu/gcc/gcc-15.2.0/gcc-15.2.0.tar.xz"
+
+    # Keep in lockstep with the gcc version used by the tsan CI job: a
+    # libstdc++ older than the compiler may lack GLIBCXX symbol versions
+    # that binaries built by that compiler reference. Checksums match the
+    # version() directives in spack's gcc package.
+    version("15.2.0", sha256="438fd996826b0c82485a29da03a72d71d6e3541a83ec702df4271f6fe025d24e")
+    version("14.3.0", sha256="e0dc77297625631ac8e50fa92fffefe899a4eb702592da5c32ef04e2293aca3a")
+
+    depends_on("c", type="build")
+    depends_on("cxx", type="build")
+    depends_on("gmake", type="build")
+
+    def install(self, spec, prefix):
+        # gthr-default.h only materializes in a configured libgcc build dir;
+        # on POSIX targets it is a verbatim copy of gthr-posix.h. Providing it
+        # up front spares building libgcc (and the in-tree compiler).
+        gthr_include = join_path(self.stage.source_path, "spack-gthr")
+        mkdirp(gthr_include)
+        copy(
+            join_path(self.stage.source_path, "libgcc", "gthr-posix.h"),
+            join_path(gthr_include, "gthr-default.h"),
+        )
+
+        flags = f"-I{gthr_include} -O2 -g -fno-omit-frame-pointer -fsanitize=thread"
+        build_dir = join_path(self.stage.source_path, "spack-build")
+        mkdirp(build_dir)
+        with working_dir(build_dir):
+            configure = Executable(
+                join_path(self.stage.source_path, "libstdc++-v3", "configure")
+            )
+            configure(
+                f"--prefix={prefix}",
+                f"--libdir={prefix.lib}",
+                "--disable-multilib",
+                "--disable-libstdcxx-pch",
+                "--enable-libstdcxx-threads=yes",
+                "--with-default-libstdcxx-abi=new",
+                f"CFLAGS={flags}",
+                f"CXXFLAGS={flags}",
+                "LDFLAGS=-fsanitize=thread",
+            )
+            make()
+            make("install")
+
+        # The runtime libraries land in the multilib os dir (lib64 on
+        # x86_64), --libdir notwithstanding (--with-toolexeclibdir only
+        # applies to cross builds); normalize to lib/ for the consumer.
+        if os.path.isdir(prefix.lib64):
+            mkdirp(prefix.lib)
+            for entry in os.listdir(prefix.lib64):
+                shutil.move(join_path(prefix.lib64, entry), join_path(prefix.lib, entry))
+            os.rmdir(prefix.lib64)
+
+        # Only the runtime library is consumed -- compilation uses the
+        # compiler's own (identical) headers. Drop the rest to keep the
+        # buildcache entry small.
+        for directory in ("include", "share"):
+            path = join_path(prefix, directory)
+            if os.path.isdir(path):
+                shutil.rmtree(path)

test/ci/spack_repo/fairmq_ci/repo.yaml

@@ -0,0 +1,3 @@
+repo:
+  namespace: fairmq_ci
+  api: v2.0