C++: Checks in prototype of cc_shared_libraryA
Design doc at:
https://docs.google.com/document/d/13nolQXvXDsJ4yjWP1FRd-WscP2-rHZcR3Zb__js6mLA/edit?ts=5dc40747#
RELNOTES:none
PiperOrigin-RevId: 279939859
Change-Id: Ib68ef39e42237962c53e72f79f0389906c4e61a5
diff --git a/examples/experimental_cc_shared_library.bzl b/examples/experimental_cc_shared_library.bzl
new file mode 100644
index 0000000..716e02c
--- /dev/null
+++ b/examples/experimental_cc_shared_library.bzl
@@ -0,0 +1,219 @@
+""" This is an experimental implementation of cc_shared_library. We may change
+the implementation at any moment or even delete this file. Do not rely on this.
+It requires bazel >1.2 and passing the flag
+--experimental_cc_shared_library
+"""
+
+load("//cc:find_cc_toolchain.bzl", "find_cc_toolchain")
+
+# TODO(#5200): Add export_define to library_to_link and cc_library
+
+GraphNodeInfo = provider(
+ fields = {
+ "children": "Other GraphNodeInfo from dependencies of this target",
+ "label": "Label of the target visited",
+ "linked_statically_by": "The value of this attribute if the target has it",
+ },
+)
+CcSharedLibraryInfo = provider(
+ fields = {
+ "dynamic_deps": "All shared libraries depended on transitively",
+ "linker_input": "the resulting linker input artifact for the shared library",
+ "exports": "cc_libraries that are linked statically and exported",
+ },
+)
+
+def _separate_static_and_dynamic_link_libraries(direct_children, can_be_linked_dynamically):
+ node = None
+ all_children = list(direct_children)
+ link_statically_labels = {}
+ link_dynamically_labels = {}
+
+ # Horrible I know. Perhaps Starlark team gives me a way to prune a tree.
+ for i in range(1, 2147483647):
+ if len(all_children) == 0:
+ break
+ node = all_children.pop(0)
+
+ if node.label in can_be_linked_dynamically:
+ link_dynamically_labels[node.label] = None
+ else:
+ link_statically_labels[node.label] = node.linked_statically_by
+ all_children.extend(node.children)
+ return (link_statically_labels, link_dynamically_labels)
+
+def _create_linker_context(ctx, static_linker_inputs, dynamic_linker_inputs):
+ linker_inputs = []
+ linker_inputs.extend(dynamic_linker_inputs)
+ linker_inputs.extend(static_linker_inputs)
+
+ return cc_common.create_linking_context(
+ linker_inputs = depset(linker_inputs),
+ )
+
+def _merge_cc_shared_library_infos(ctx):
+ dynamic_deps = []
+ transitive_dynamic_deps = []
+ for dep in ctx.attr.dynamic_deps:
+ dynamic_dep_entry = (
+ dep[CcSharedLibraryInfo].exports,
+ dep[CcSharedLibraryInfo].linker_input,
+ )
+ dynamic_deps.append(dynamic_dep_entry)
+ transitive_dynamic_deps.append(dep[CcSharedLibraryInfo].dynamic_deps)
+
+ return depset(direct = dynamic_deps, transitive = transitive_dynamic_deps)
+
+def _build_exports_map_from_only_dynamic_deps(merged_shared_library_infos):
+ exports_map = {}
+ for entry in merged_shared_library_infos.to_list():
+ exports = entry[0]
+ linker_input = entry[1]
+ for export in exports:
+ str_export_label = str(export.label)
+ if str_export_label in exports_map:
+ fail("Two shared libraries in dependencies export the same symbols. Both " +
+ exports_map[str_export_label].libraries[0].dynamic_library.short_path +
+ " and " + linker_input.dynamic_library.short_path +
+ " export " + str_export_label)
+ exports_map[str(export.label)] = linker_input
+ return exports_map
+
+def _filter_inputs(ctx, transitive_exports):
+ static_linker_inputs = []
+ dynamic_linker_inputs = []
+
+ graph_structure_aspect_nodes = []
+ linker_inputs = []
+ for export in ctx.attr.exports:
+ linker_inputs.extend(export[CcInfo].linking_context.linker_inputs.to_list())
+ graph_structure_aspect_nodes.append(export[GraphNodeInfo])
+
+ can_be_linked_dynamically = {}
+ for linker_input in linker_inputs:
+ owner = str(linker_input.owner)
+ if owner in transitive_exports:
+ can_be_linked_dynamically[owner] = True
+
+ (link_statically_labels, link_dynamically_labels) = _separate_static_and_dynamic_link_libraries(
+ graph_structure_aspect_nodes,
+ can_be_linked_dynamically,
+ )
+
+ already_linked_dynamically = {}
+ for linker_input in linker_inputs:
+ owner = str(linker_input.owner)
+ if owner in link_dynamically_labels:
+ dynamic_linker_input = transitive_exports[owner]
+ if str(dynamic_linker_input.owner) not in already_linked_dynamically:
+ already_linked_dynamically[str(dynamic_linker_input.owner)] = True
+ dynamic_linker_inputs.append(dynamic_linker_input)
+ elif owner in link_statically_labels:
+ can_be_linked_statically = False
+ for linked_statically_by in link_statically_labels[owner]:
+ if linked_statically_by == str(ctx.label):
+ can_be_linked_statically = True
+ static_linker_inputs.append(linker_input)
+ break
+ if not can_be_linked_statically:
+ fail("We can't link " +
+ str(owner) + " either statically or dynamically")
+ else:
+ fail("Implementation error, this should not happen")
+
+ # Every direct dynamic_dep of this rule will be linked dynamically even if we
+ # didn't reach a cc_library exported by one of these dynamic_deps. In other
+ # words, the shared library might link more shared libraries than we need
+ # in the cc_library graph.
+ for dep in ctx.attr.dynamic_deps:
+ has_a_used_export = False
+ for export in dep[CcSharedLibraryInfo].exports:
+ if str(export.label) in link_dynamically_labels:
+ has_a_used_export = True
+ break
+ if not has_a_used_export:
+ dynamic_linker_inputs.append(dep[CcSharedLibraryInfo].linker_input)
+
+ return (static_linker_inputs, dynamic_linker_inputs)
+
+def _cc_shared_library_impl(ctx):
+ cc_toolchain = find_cc_toolchain(ctx)
+ feature_configuration = cc_common.configure_features(
+ ctx = ctx,
+ cc_toolchain = cc_toolchain,
+ requested_features = ctx.features,
+ unsupported_features = ctx.disabled_features,
+ )
+
+ merged_cc_shared_library_info = _merge_cc_shared_library_infos(ctx)
+ exports_map = _build_exports_map_from_only_dynamic_deps(merged_cc_shared_library_info)
+ for export in ctx.attr.exports:
+ if str(export.label) in exports_map:
+ fail("Trying to export a library already exported by a different shared library: " + str(export.label))
+ (static_linker_inputs, dynamic_linker_inputs) = _filter_inputs(ctx, exports_map)
+
+ linking_context = _create_linker_context(ctx, static_linker_inputs, dynamic_linker_inputs)
+
+ user_link_flags = []
+ additional_inputs = []
+ if ctx.file.visibility_file != None:
+ user_link_flags = [
+ "-Wl,--no-undefined", # Just here for testing.
+ "-Wl,--version-script=" + ctx.file.visibility_file.path,
+ ]
+ additional_inputs = [ctx.file.visibility_file]
+
+ linking_outputs = cc_common.link(
+ actions = ctx.actions,
+ feature_configuration = feature_configuration,
+ cc_toolchain = cc_toolchain,
+ linking_contexts = [linking_context],
+ user_link_flags = user_link_flags,
+ additional_inputs = additional_inputs,
+ name = ctx.label.name,
+ output_type = "dynamic_library",
+ )
+
+ return [
+ DefaultInfo(files = depset([linking_outputs.library_to_link.resolved_symlink_dynamic_library])),
+ CcSharedLibraryInfo(
+ dynamic_deps = merged_cc_shared_library_info,
+ exports = ctx.attr.exports,
+ linker_input = cc_common.create_linker_input(owner = ctx.label, libraries = depset([linking_outputs.library_to_link])),
+ ),
+ ]
+
+def _graph_structure_aspect_impl(target, ctx):
+ children = []
+
+ if hasattr(ctx.rule.attr, "deps"):
+ for dep in ctx.rule.attr.deps:
+ if GraphNodeInfo in dep:
+ children.append(dep[GraphNodeInfo])
+
+ linked_statically_by = []
+ if hasattr(ctx.rule.attr, "linked_statically_by"):
+ linked_statically_by = ctx.rule.attr.linked_statically_by
+
+ return [GraphNodeInfo(
+ label = str(ctx.label),
+ linked_statically_by = linked_statically_by,
+ children = children,
+ )]
+
+graph_structure_aspect = aspect(
+ attr_aspects = ["*"],
+ implementation = _graph_structure_aspect_impl,
+)
+
+cc_shared_library = rule(
+ implementation = _cc_shared_library_impl,
+ attrs = {
+ "dynamic_deps": attr.label_list(providers = [CcSharedLibraryInfo]),
+ "visibility_file": attr.label(allow_single_file = True),
+ "exports": attr.label_list(aspects = [graph_structure_aspect]),
+ "_cc_toolchain": attr.label(default = "@bazel_tools//tools/cpp:current_cc_toolchain"),
+ },
+ toolchains = ["//cc:toolchain_type"],
+ fragments = ["cpp"],
+)
