Compiler.default_libc

Some logic to detect what libc the c / cxx compilers use by default,
based on `-dynamic-linker`.

The function `compiler.default_libc()` returns a `Spec` of the form
`glibc@x.y` or `musl@x.y` with the `external_path` property set.

The idea is this can be injected as a dependency.

If we can't run the dynamic linker directly, fall back to `ldd` relative
to the prefix computed from `ld.so.`

etc/spack/defaults/packages.yaml

@@ -35,6 +35,7 @@ packages:
       java: [openjdk, jdk, ibm-java]
       jpeg: [libjpeg-turbo, libjpeg]
       lapack: [openblas, amdlibflame]
+      libc: [glibc, musl]
       libgfortran: [ gcc-runtime ]
       libglx: [mesa+glx, mesa18+glx]
       libifcore: [ intel-oneapi-runtime ]

lib/spack/spack/compiler.py

@@ -8,9 +8,11 @@
 import os
 import platform
 import re
+import shlex
 import shutil
 import sys
 import tempfile
+from subprocess import PIPE, run
 from typing import List, Optional, Sequence
 
 import llnl.path
@@ -184,6 +186,113 @@ def _parse_non_system_link_dirs(string: str) -> List[str]:
     return list(p for p in link_dirs if not in_system_subdirectory(p))
 
 
+def _parse_dynamic_linker(output: str):
+    """Parse -dynamic-linker /path/to/ld.so from compiler output"""
+    for line in reversed(output.splitlines()):
+        if "-dynamic-linker" not in line:
+            continue
+        args = shlex.split(line)
+
+        for idx in reversed(range(1, len(args))):
+            arg = args[idx]
+            if arg == "-dynamic-linker" or args == "--dynamic-linker":
+                return args[idx + 1]
+            elif arg.startswith("--dynamic-linker=") or arg.startswith("-dynamic-linker="):
+                return arg.split("=", 1)[1]
+
+
+def _libc_from_ldd(ldd: str) -> Optional["spack.spec.Spec"]:
+    try:
+        result = run([ldd, "--version"], stdout=PIPE, stderr=PIPE, check=False)
+        stdout = result.stdout.decode("utf-8")
+    except Exception:
+        return None
+
+    if not re.search("gnu|glibc", stdout, re.IGNORECASE):
+        return None
+
+    version_str = re.match(r".+\(.+\) (.+)", stdout)
+    if not version_str:
+        return None
+    try:
+        return spack.spec.Spec(f"glibc@={version_str.group(1)}")
+    except Exception:
+        return None
+
+
+def _libc_from_dynamic_linker(dynamic_linker: str) -> Optional["spack.spec.Spec"]:
+    if not os.path.exists(dynamic_linker):
+        return None
+
+    # The dynamic linker is usually installed in the same /lib(64)?/ld-*.so path across all
+    # distros. The rest of libc is elsewhere, e.g. /usr. Typically the dynamic linker is then
+    # a symlink into /usr/lib, which we use to for determining the actual install prefix of
+    # libc.
+    realpath = os.path.realpath(dynamic_linker)
+
+    prefix = os.path.dirname(realpath)
+    # Remove the multiarch suffix if it exists
+    if os.path.basename(prefix) not in ("lib", "lib64"):
+        prefix = os.path.dirname(prefix)
+
+    # Non-standard install layout -- just bail.
+    if os.path.basename(prefix) not in ("lib", "lib64"):
+        return None
+
+    prefix = os.path.dirname(prefix)
+
+    # Now try to figure out if glibc or musl, which is the only ones we support.
+    # In recent glibc we can simply execute the dynamic loader. In musl that's always the case.
+    try:
+        result = run([dynamic_linker, "--version"], stdout=PIPE, stderr=PIPE, check=False)
+        stdout = result.stdout.decode("utf-8")
+        stderr = result.stderr.decode("utf-8")
+    except Exception:
+        return None
+
+    # musl prints to stderr
+    if stderr.startswith("musl libc"):
+        version_str = re.search(r"^Version (.+)$", stderr, re.MULTILINE)
+        if not version_str:
+            return None
+        try:
+            spec = spack.spec.Spec(f"musl@={version_str.group(1)}")
+            spec.external_path = prefix
+            return spec
+        except Exception:
+            return None
+    elif re.search("gnu|glibc", stdout, re.IGNORECASE):
+        # output is like "ld.so (...) stable release version 2.33." write a regex for it
+        match = re.search(r"version (\d+\.\d+(?:\.\d+)?)", stdout)
+        if not match:
+            return None
+        try:
+            version = match.group(1)
+            spec = spack.spec.Spec(f"glibc@={version}")
+            spec.external_path = prefix
+            return spec
+        except Exception:
+            return None
+    else:
+        # Could not get the version by running the dynamic linker directly. Instead locate `ldd`
+        # relative to the dynamic linker.
+        ldd = os.path.join(prefix, "bin", "ldd")
+        if not os.path.exists(ldd):
+            # If `/lib64/ld.so` was not a symlink to `/usr/lib/ld.so` we can try to use /usr as
+            # prefix. This is the case on ubuntu 18.04 where /lib != /usr/lib.
+            if prefix != "/":
+                return None
+            prefix = "/usr"
+            ldd = os.path.join(prefix, "bin", "ldd")
+            if not os.path.exists(ldd):
+                return None
+        maybe_spec = _libc_from_ldd(ldd)
+        if not maybe_spec:
+            return None
+        maybe_spec.external_path = prefix
+        return maybe_spec
+
+
 def in_system_subdirectory(path):
     system_dirs = [
         "/lib/",
@@ -417,17 +526,33 @@ def real_version(self):
                 self._real_version = self.version
         return self._real_version
 
-    def implicit_rpaths(self):
+    def implicit_rpaths(self) -> List[str]:
         if self.enable_implicit_rpaths is False:
             return []
 
-        # Put CXX first since it has the most linking issues
-        # And because it has flags that affect linking
-        link_dirs = self._get_compiler_link_paths()
+        output = self.compiler_verbose_output
+
+        if not output:
+            return []
+
+        link_dirs = _parse_non_system_link_dirs(output)
 
         all_required_libs = list(self.required_libs) + Compiler._all_compiler_rpath_libraries
         return list(paths_containing_libs(link_dirs, all_required_libs))
 
+    def default_libc(self) -> Optional["spack.spec.Spec"]:
+        output = self.compiler_verbose_output
+
+        if not output:
+            return None
+
+        dynamic_linker = _parse_dynamic_linker(output)
+
+        if not dynamic_linker:
+            return None
+
+        return _libc_from_dynamic_linker(dynamic_linker)
+
     @property
     def required_libs(self):
         """For executables created with this compiler, the compiler libraries
@@ -436,17 +561,17 @@ def required_libs(self):
         # By default every compiler returns the empty list
         return []
 
-    def _get_compiler_link_paths(self):
+    @property
+    def compiler_verbose_output(self) -> Optional[str]:
+        """Verbose output from compiling a dummy C source file. Output is cached."""
+        if not hasattr(self, "_compile_c_source_output"):
+            self._compile_c_source_output = self._compile_dummy_c_source()
+        return self._compile_c_source_output
+
+    def _compile_dummy_c_source(self) -> Optional[str]:
         cc = self.cc if self.cc else self.cxx
         if not cc or not self.verbose_flag:
-            # Cannot determine implicit link paths without a compiler / verbose flag
-            return []
-
-        # What flag types apply to first_compiler, in what order
-        if cc == self.cc:
-            flags = ["cflags", "cppflags", "ldflags"]
-        else:
-            flags = ["cxxflags", "cppflags", "ldflags"]
+            return None
 
         try:
             tmpdir = tempfile.mkdtemp(prefix="spack-implicit-link-info")
@@ -458,20 +583,19 @@ def _get_compiler_link_paths(self):
                     "int main(int argc, char* argv[]) { (void)argc; (void)argv; return 0; }\n"
                 )
             cc_exe = spack.util.executable.Executable(cc)
-            for flag_type in flags:
+            for flag_type in ["cflags" if cc == self.cc else "cxxflags", "cppflags", "ldflags"]:
                 cc_exe.add_default_arg(*self.flags.get(flag_type, []))
 
             with self.compiler_environment():
-                output = cc_exe(self.verbose_flag, fin, "-o", fout, output=str, error=str)
-            return _parse_non_system_link_dirs(output)
+                return cc_exe(self.verbose_flag, fin, "-o", fout, output=str, error=str)
         except spack.util.executable.ProcessError as pe:
             tty.debug("ProcessError: Command exited with non-zero status: " + pe.long_message)
-            return []
+            return None
         finally:
             shutil.rmtree(tmpdir, ignore_errors=True)
 
     @property
-    def verbose_flag(self):
+    def verbose_flag(self) -> Optional[str]:
         """
         This property should be overridden in the compiler subclass if a
         verbose flag is available.

lib/spack/spack/compilers/nag.py

@@ -64,7 +64,7 @@ def verbose_flag(self):
         #
         # This way, we at least enable the implicit rpath detection, which is
         # based on compilation of a C file (see method
-        # spack.compiler._get_compiler_link_paths): in the case of a mixed
+        # spack.compiler._compile_dummy_c_source): in the case of a mixed
         # NAG/GCC toolchain, the flag will be passed to g++ (e.g.
         # 'g++ -Wl,-v ./main.c'), otherwise, the flag will be passed to nagfor
         # (e.g. 'nagfor -Wl,-v ./main.c' - note that nagfor recognizes '.c'

lib/spack/spack/solver/asp.py

@@ -566,6 +566,23 @@ def _spec_with_default_name(spec_str, name):
     return spec
 
 
+def _external_config_with_implictit_externals():
+    # Read packages.yaml and normalize it, so that it will not contain entries referring to
+    # virtual packages.
+    packages_yaml = _normalize_packages_yaml(spack.config.get("packages"))
+
+    # Add externals for libc from compilers on Linux
+    if spack.platforms.host().name != "linux":
+        return packages_yaml
+
+    for compiler in all_compilers_in_config():
+        libc = compiler.default_libc()
+        if libc:
+            entry = {"spec": f"{libc} %{compiler.spec}", "prefix": libc.external_path}
+            packages_yaml.setdefault(libc.name, {}).setdefault("externals", []).append(entry)
+    return packages_yaml
+
+
 class ErrorHandler:
     def __init__(self, model):
         self.model = model
@@ -1554,12 +1571,8 @@ def emit_facts_from_requirement_rules(self, rules: List[RequirementRule]):
                 requirement_weight += 1
 
     def external_packages(self):
-        """Facts on external packages, as read from packages.yaml"""
-        # Read packages.yaml and normalize it, so that it
-        # will not contain entries referring to virtual
-        # packages.
-        packages_yaml = spack.config.get("packages")
-        packages_yaml = _normalize_packages_yaml(packages_yaml)
+        """Facts on external packages, from packages.yaml and implicit externals."""
+        packages_yaml = _external_config_with_implictit_externals()
 
         self.gen.h1("External packages")
         for pkg_name, data in packages_yaml.items():
@@ -3185,12 +3198,8 @@ def no_flags(self, node, flag_type):
         self._specs[node].compiler_flags[flag_type] = []
 
     def external_spec_selected(self, node, idx):
-        """This means that the external spec and index idx
-        has been selected for this package.
-        """
-
-        packages_yaml = spack.config.get("packages")
-        packages_yaml = _normalize_packages_yaml(packages_yaml)
+        """This means that the external spec and index idx has been selected for this package."""
+        packages_yaml = _external_config_with_implictit_externals()
         spec_info = packages_yaml[node.pkg]["externals"][int(idx)]
         self._specs[node].external_path = spec_info.get("prefix", None)
         self._specs[node].external_modules = spack.spec.Spec._format_module_list(

lib/spack/spack/solver/os_compatibility.lp

@@ -12,16 +12,3 @@
 % macOS
 os_compatible("monterey", "bigsur").
 os_compatible("bigsur", "catalina").
-
-% Ubuntu
-os_compatible("ubuntu22.04", "ubuntu21.10").
-os_compatible("ubuntu21.10", "ubuntu21.04").
-os_compatible("ubuntu21.04", "ubuntu20.10").
-os_compatible("ubuntu20.10", "ubuntu20.04").
-os_compatible("ubuntu20.04", "ubuntu19.10").
-os_compatible("ubuntu19.10", "ubuntu19.04").
-os_compatible("ubuntu19.04", "ubuntu18.10").
-os_compatible("ubuntu18.10", "ubuntu18.04").
-
-%EL8
-os_compatible("rhel8", "rocky8").

lib/spack/spack/test/compilers/basics.py

@@ -14,6 +14,7 @@
 import spack.compilers
 import spack.spec
 import spack.util.environment
+import spack.util.module_cmd
 from spack.compiler import Compiler
 from spack.util.executable import Executable, ProcessError
 
@@ -137,14 +138,6 @@ def __init__(self):
             environment={},
         )
 
-    def _get_compiler_link_paths(self):
-        # Mock os.path.isdir so the link paths don't have to exist
-        old_isdir = os.path.isdir
-        os.path.isdir = lambda x: True
-        ret = super()._get_compiler_link_paths()
-        os.path.isdir = old_isdir
-        return ret
-
     @property
     def name(self):
         return "mockcompiler"
@@ -162,34 +155,25 @@ def verbose_flag(self):
     required_libs = ["libgfortran"]
 
 
-def test_implicit_rpaths(dirs_with_libfiles, monkeypatch):
+@pytest.mark.not_on_windows("Not supported on Windows (yet)")
+def test_implicit_rpaths(dirs_with_libfiles):
     lib_to_dirs, all_dirs = dirs_with_libfiles
-
-    def try_all_dirs(*args):
-        return all_dirs
-
-    monkeypatch.setattr(MockCompiler, "_get_compiler_link_paths", try_all_dirs)
-
-    expected_rpaths = set(lib_to_dirs["libstdc++"] + lib_to_dirs["libgfortran"])
-
     compiler = MockCompiler()
+    compiler._compile_c_source_output = "ld " + " ".join(f"-L{d}" for d in all_dirs)
     retrieved_rpaths = compiler.implicit_rpaths()
-    assert set(retrieved_rpaths) == expected_rpaths
+    assert set(retrieved_rpaths) == set(lib_to_dirs["libstdc++"] + lib_to_dirs["libgfortran"])
 
 
-no_flag_dirs = ["/path/to/first/lib", "/path/to/second/lib64"]
-no_flag_output = "ld -L%s -L%s" % tuple(no_flag_dirs)
-
-flag_dirs = ["/path/to/first/with/flag/lib", "/path/to/second/lib64"]
-flag_output = "ld -L%s -L%s" % tuple(flag_dirs)
+without_flag_output = "ld -L/path/to/first/lib -L/path/to/second/lib64"
+with_flag_output = "ld -L/path/to/first/with/flag/lib -L/path/to/second/lib64"
 
 
 def call_compiler(exe, *args, **kwargs):
     # This method can replace Executable.__call__ to emulate a compiler that
     # changes libraries depending on a flag.
     if "--correct-flag" in exe.exe:
-        return flag_output
-    return no_flag_output
+        return with_flag_output
+    return without_flag_output
 
 
 @pytest.mark.not_on_windows("Not supported on Windows (yet)")
@@ -203,8 +187,8 @@ def call_compiler(exe, *args, **kwargs):
         ("cc", "cppflags"),
     ],
 )
-@pytest.mark.enable_compiler_link_paths
-def test_get_compiler_link_paths(monkeypatch, exe, flagname):
+@pytest.mark.enable_compiler_execution
+def test_compile_dummy_c_source_adds_flags(monkeypatch, exe, flagname):
     # create fake compiler that emits mock verbose output
     compiler = MockCompiler()
     monkeypatch.setattr(Executable, "__call__", call_compiler)
@@ -221,40 +205,38 @@ def test_get_compiler_link_paths(monkeypatch, exe, flagname):
         assert False
 
     # Test without flags
-    assert compiler._get_compiler_link_paths() == no_flag_dirs
+    assert compiler._compile_dummy_c_source() == without_flag_output
 
     if flagname:
         # set flags and test
         compiler.flags = {flagname: ["--correct-flag"]}
-        assert compiler._get_compiler_link_paths() == flag_dirs
+        assert compiler._compile_dummy_c_source() == with_flag_output
 
 
-def test_get_compiler_link_paths_no_path():
+@pytest.mark.enable_compiler_execution
+def test_compile_dummy_c_source_no_path():
     compiler = MockCompiler()
     compiler.cc = None
     compiler.cxx = None
-    compiler.f77 = None
-    compiler.fc = None
-    assert compiler._get_compiler_link_paths() == []
+    assert compiler._compile_dummy_c_source() is None
 
 
-def test_get_compiler_link_paths_no_verbose_flag():
+@pytest.mark.enable_compiler_execution
+def test_compile_dummy_c_source_no_verbose_flag():
     compiler = MockCompiler()
     compiler._verbose_flag = None
-    assert compiler._get_compiler_link_paths() == []
+    assert compiler._compile_dummy_c_source() is None
 
 
 @pytest.mark.not_on_windows("Not supported on Windows (yet)")
-@pytest.mark.enable_compiler_link_paths
-def test_get_compiler_link_paths_load_env(working_env, monkeypatch, tmpdir):
+@pytest.mark.enable_compiler_execution
+def test_compile_dummy_c_source_load_env(working_env, monkeypatch, tmpdir):
     gcc = str(tmpdir.join("gcc"))
     with open(gcc, "w") as f:
         f.write(
-            """#!/bin/sh
+            f"""#!/bin/sh
 if [ "$ENV_SET" = "1" ] && [ "$MODULE_LOADED" = "1" ]; then
-  echo '"""
-            + no_flag_output
-            + """'
+  printf '{without_flag_output}'
 fi
 """
         )
@@ -274,7 +256,7 @@ def module(*args):
     compiler.environment = {"set": {"ENV_SET": "1"}}
     compiler.modules = ["turn_on"]
 
-    assert compiler._get_compiler_link_paths() == no_flag_dirs
+    assert compiler._compile_dummy_c_source() == without_flag_output
 
 
 # Get the desired flag from the specified compiler spec.

lib/spack/spack/test/conftest.py

@@ -34,6 +34,7 @@
 import spack.binary_distribution
 import spack.caches
 import spack.cmd.buildcache
+import spack.compiler
 import spack.compilers
 import spack.config
 import spack.database
@@ -269,10 +270,6 @@ def clean_test_environment():
     ev.deactivate()
 
 
-def _verify_executables_noop(*args):
-    return None
-
-
 def _host():
     """Mock archspec host so there is no inconsistency on the Windows platform
     This function cannot be local as it needs to be pickleable"""
@@ -298,9 +295,7 @@ def mock_compiler_executable_verification(request, monkeypatch):
 
     If a test is marked in that way this is a no-op."""
     if "enable_compiler_verification" not in request.keywords:
-        monkeypatch.setattr(
-            spack.compiler.Compiler, "verify_executables", _verify_executables_noop
-        )
+        monkeypatch.setattr(spack.compiler.Compiler, "verify_executables", _return_none)
 
 
 # Hooks to add command line options or set other custom behaviors.
@@ -934,26 +929,16 @@ def dirs_with_libfiles(tmpdir_factory):
     yield lib_to_dirs, all_dirs
 
 
-def _compiler_link_paths_noop(*args):
-    return []
+def _return_none(*args):
+    return None
 
 
 @pytest.fixture(scope="function", autouse=True)
 def disable_compiler_execution(monkeypatch, request):
-    """
-    This fixture can be disabled for tests of the compiler link path
-    functionality by::
-
-        @pytest.mark.enable_compiler_link_paths
-
-    If a test is marked in that way this is a no-op."""
-    if "enable_compiler_link_paths" not in request.keywords:
-        # Compiler.determine_implicit_rpaths actually runs the compiler. So
-        # replace that function with a noop that simulates finding no implicit
-        # RPATHs
-        monkeypatch.setattr(
-            spack.compiler.Compiler, "_get_compiler_link_paths", _compiler_link_paths_noop
-        )
+    """Disable compiler execution to determine implicit link paths and libc flavor and version.
+    To re-enable use `@pytest.mark.enable_compiler_execution`"""
+    if "enable_compiler_execution" not in request.keywords:
+        monkeypatch.setattr(spack.compiler.Compiler, "_compile_dummy_c_source", _return_none)
 
 
 @pytest.fixture(scope="function")

pytest.ini

@@ -12,7 +12,7 @@ markers =
   requires_executables: tests that requires certain executables in PATH to run
   nomockstage: use a stage area specifically created for this test, instead of relying on a common mock stage
   enable_compiler_verification: enable compiler verification within unit tests
-  enable_compiler_link_paths: verifies compiler link paths within unit tests
+  enable_compiler_execution: enable compiler execution to detect link paths and libc
   disable_clean_stage_check: avoid failing tests if there are leftover files in the stage area
   only_clingo: mark unit tests that run only with clingo
   only_original: mark unit tests that are specific to the original concretizer

var/spack/repos/builtin/packages/gcc/package.py

@@ -1185,5 +1185,13 @@ def runtime_constraints(cls, *, spec, pkg):
                 description=f"Add a dependency on '{gfortran_str}' for nodes compiled with "
                 f"{str(spec)} and using the 'fortran' language",
             )
+
+        libc = compiler.default_libc()
+
+        if libc:
+            pkg("*").depends_on(
+                str(libc), when=f"%{str(compiler.spec)}", type="link", description="Add libc"
+            )
+
         # The version of gcc-runtime is the same as the %gcc used to "compile" it
         pkg("gcc-runtime").requires(f"@={str(spec.version)}", when=f"%{str(spec)}")

var/spack/repos/builtin/packages/glibc/package.py

@@ -20,9 +20,12 @@ class Glibc(AutotoolsPackage, GNUMirrorPackage):
     maintainers("haampie")
 
     build_directory = "build"
+    tags = ["runtime"]
 
     license("LGPL-2.1-or-later")
 
+    provides("libc")
+
     version("master", branch="master")
     version("2.39", sha256="97f84f3b7588cd54093a6f6389b0c1a81e70d99708d74963a2e3eab7c7dc942d")
     version("2.38", sha256="16e51e0455e288f03380b436e41d5927c60945abd86d0c9852b84be57dd6ed5e")

var/spack/repos/builtin/packages/musl/package.py

@@ -25,9 +25,12 @@ class Musl(MakefilePackage):
 
     homepage = "https://www.musl-libc.org"
     url = "https://www.musl-libc.org/releases/musl-1.1.23.tar.gz"
+    tags = ["runtime"]
 
     license("MIT")
 
+    provides("libc")
+
     version("1.2.4", sha256="7a35eae33d5372a7c0da1188de798726f68825513b7ae3ebe97aaaa52114f039")
     version("1.2.3", sha256="7d5b0b6062521e4627e099e4c9dc8248d32a30285e959b7eecaa780cf8cfd4a4")
     version("1.2.2", sha256="9b969322012d796dc23dda27a35866034fa67d8fb67e0e2c45c913c3d43219dd")