gcc: generate spec file and fix external libc default paths after install from cache (#43839)

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

3 files changed, 69 insertions, 0 deletions

diff --git a/var/spack/repos/builtin/packages/gcc/package.py b/var/spack/repos/builtin/packages/gcc/package.py
index b70ff7586d..6d94e2785d 100644
--- a/var/spack/repos/builtin/packages/gcc/package.py
+++ b/var/spack/repos/builtin/packages/gcc/package.py
@@ -16,6 +16,7 @@ from llnl.util.symlink import readlink
 
 import spack.platforms
 import spack.util.executable
+import spack.util.libc
 from spack.operating_systems.mac_os import macos_sdk_path, macos_version
 from spack.package import *
 
@@ -1152,3 +1153,63 @@ class Gcc(AutotoolsPackage, GNUMirrorPackage):
             )
         # 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)}")
+
+    def _post_buildcache_install_hook(self):
+        if not self.spec.satisfies("platform=linux"):
+            return
+
+        # Setting up the runtime environment shouldn't be necessary here.
+        relocation_args = []
+        gcc = self.spec["gcc"].command
+        specs_file = os.path.join(self.spec_dir, "specs")
+        dryrun = gcc("test.c", "-###", output=os.devnull, error=str).strip()
+        if not dryrun:
+            tty.warn(f"Cannot relocate {specs_file}, compiler might not be working properly")
+            return
+        dynamic_linker = spack.util.libc.parse_dynamic_linker(dryrun)
+        if not dynamic_linker:
+            tty.warn(f"Cannot relocate {specs_file}, compiler might not be working properly")
+            return
+
+        libc = spack.util.libc.libc_from_dynamic_linker(dynamic_linker)
+
+        # We search for crt1.o ourselves because `gcc -print-prile-name=crt1.o` can give a rather
+        # convoluted relative path from a different prefix.
+        startfile_prefix = spack.util.libc.startfile_prefix(libc.external_path, dynamic_linker)
+
+        gcc_can_locate = lambda p: os.path.isabs(
+            gcc(f"-print-file-name={p}", output=str, error=os.devnull).strip()
+        )
+
+        if not gcc_can_locate("crt1.o"):
+            relocation_args.append(f"-B{startfile_prefix}")
+
+        # libc headers may also be in a multiarch subdir.
+        header_dir = spack.util.libc.libc_include_dir_from_startfile_prefix(
+            libc.external_path, startfile_prefix
+        )
+        if header_dir and all(
+            os.path.exists(os.path.join(header_dir, h))
+            for h in libc.package_class.representative_headers
+        ):
+            relocation_args.append(f"-isystem {header_dir}")
+        else:
+            tty.warn(
+                f"Cannot relocate {specs_file} include directories, "
+                f"compiler might not be working properly"
+            )
+
+        # Delete current spec files.
+        try:
+            os.unlink(specs_file)
+        except OSError:
+            pass
+
+        # Write a new one and append flags for libc
+        self.write_specs_file()
+
+        if relocation_args:
+            with open(specs_file, "a") as f:
+                print("*self_spec:", file=f)
+                print(f"+ {' '.join(relocation_args)}", file=f)
+                print(file=f)
diff --git a/var/spack/repos/builtin/packages/glibc/package.py b/var/spack/repos/builtin/packages/glibc/package.py
index 16315c4bbc..f09f455ab6 100644
--- a/var/spack/repos/builtin/packages/glibc/package.py
+++ b/var/spack/repos/builtin/packages/glibc/package.py
@@ -22,6 +22,10 @@ class Glibc(AutotoolsPackage, GNUMirrorPackage):
     build_directory = "build"
     tags = ["runtime"]
 
+    # This is used when the package is external and we need to find the actual default include path
+    # which may be in a multiarch subdir.
+    representative_headers = ["ieee754.h"]
+
     license("LGPL-2.1-or-later")
 
     provides("libc")
diff --git a/var/spack/repos/builtin/packages/musl/package.py b/var/spack/repos/builtin/packages/musl/package.py
index 4b503feb64..622bd004e8 100644
--- a/var/spack/repos/builtin/packages/musl/package.py
+++ b/var/spack/repos/builtin/packages/musl/package.py
@@ -29,6 +29,10 @@ class Musl(MakefilePackage):
 
     license("MIT")
 
+    # This is used when the package is external and we need to find the actual default include path
+    # which may be in a multiarch subdir.
+    representative_headers = ["iso646.h"]
+
     provides("libc")
 
     version("1.2.4", sha256="7a35eae33d5372a7c0da1188de798726f68825513b7ae3ebe97aaaa52114f039")