scons: Use either the "build" or "gem5.build" as build anchor.

If gem5.build already exists within a directory, then that build
directory can be used without having to worry about variants.

If it doesn't exist and we find a build/${VARIANT} style path, then we
use that as the anchor.

In either case, the variant name is the final component of the build
path. The parse_build_path function had been separating that out, but it
was just put back onto the path again anyway by the only caller, and
then split out again when that path was consumed. We save a step by not
splitting it out in parse_build_path.

Change-Id: I8705b3dbb7664748f5525869cb188df70319d403

SConstruct

@@ -240,27 +240,9 @@ def makePathListAbsolute(path_list, root=GetLaunchDir()):
 # doesn't work (obviously!).
 BUILD_TARGETS[:] = makePathListAbsolute(BUILD_TARGETS)
 
-# Generate a list of the unique build roots and configs that the
-# collected targets reference.
-variant_paths = set()
-build_root = None
-for t in BUILD_TARGETS:
-    this_build_root, variant = parse_build_path(t)
-
-    # Make sure all targets use the same build root.
-    if not build_root:
-        build_root = this_build_root
-    elif this_build_root != build_root:
-        error("build targets not under same build root\n  %s\n  %s" %
-            (build_root, this_build_root))
-
-    # Collect all the variants into a set.
-    variant_paths.add(os.path.join('/', build_root, variant))
-
-# Make sure build_root exists (might not if this is the first build there)
-if not isdir(build_root):
-    mkdir(build_root)
-main['BUILDROOT'] = build_root
+# Generate a list of the unique build directories that the collected targets
+# reference.
+variant_paths = set(map(parse_build_path, BUILD_TARGETS))
 
 
 ########################################################################
@@ -395,7 +377,7 @@ for variant_path in variant_paths:
     env = main.Clone()
     env['BUILDDIR'] = variant_path
 
-    gem5_build = os.path.join(build_root, variant_path, 'gem5.build')
+    gem5_build = os.path.join(variant_path, 'gem5.build')
     env['GEM5BUILD'] = gem5_build
     Execute(Mkdir(gem5_build))
 

site_scons/gem5_scons/__init__.py

@@ -39,6 +39,7 @@
 # OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 import os
+import os.path
 import pickle
 import sys
 import tempfile
@@ -56,7 +57,7 @@ termcap = get_termcap()
 def strip_build_path(path, env):
     path = str(path)
     build_base = "build/"
-    variant_base = env["BUILDROOT"] + os.path.sep
+    variant_base = os.path.dirname(env["BUILDDIR"]) + os.path.sep
     if path.startswith(variant_base):
         path = path[len(variant_base) :]
     elif path.startswith(build_base):
@@ -117,7 +118,7 @@ class Transform:
         source = source[0 : self.max_sources]
 
         def strip(f):
-            return strip_build_path(str(f), env)
+            return strip_build_path(f, env)
 
         if len(source) > 0:
             srcs = list(map(strip, source))
@@ -255,18 +256,21 @@ def error(*args, **kwargs):
 def parse_build_path(target):
     path_dirs = target.split("/")
 
-    # Pop off the target file.
+    # Search backwards for a directory with a gem5.build sub-directory, or a
+    # directory who's parent is called "build". gem5.build identifies an
+    # existing gem5 build directory. A directory called "build" is an anchor
+    # for a legacy "build/${VARIANT}/${TARGET}" style build path, where the
+    # variant selects a default config to use.
+    while path_dirs:
+        dot_gem5 = os.path.join("/", *path_dirs, "gem5.build")
+        if (
+            os.path.isdir(dot_gem5)
+            or len(path_dirs) > 1
+            and path_dirs[-2] == "build"
+        ):
+            return os.path.join("/", *path_dirs)
         path_dirs.pop()
-
-    # Search backwards for the "build" directory. Whatever was just before it
-    # was the name of the variant.
-    variant_dir = path_dirs.pop()
-    while path_dirs and path_dirs[-1] != "build":
-        variant_dir = path_dirs.pop()
-    if not path_dirs:
-        error("No non-leaf 'build' dir found on target path.", target)
-
-    return os.path.join("/", *path_dirs), variant_dir
+    error(f"No existing build directory and no variant for {target}")
 
 
 # The MakeAction wrapper, and a SCons tool to set up the *COMSTR variables.