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authorGravatar Yun Peng <pcloudy@google.com>2017-09-15 15:59:14 +0200
committerGravatar László Csomor <laszlocsomor@google.com>2017-09-18 11:25:37 +0200
commit394211bf88b88c25036429e99894fa7c60eaaace (patch)
treea5a99354a9f3b8530bb0d98d61d8844b21348ecd /tools/def_parser
parentf8480fac37692083b2f9c4e69b9b9e9e2c9b1853 (diff)
Bazel now can build dynamic library from cc_library
Working towards: https://github.com/bazelbuild/bazel/issues/3311 When building dynamic library on Windows, Bazel builds an import library and a DLL. Bazel provides a feature called windows_export_all_symbols, if this feature is enabled(and no_windows_export_all_symbols is not) for a cc_library, then Bazel parses object files of that cc_library to generate a DEF file that will be used during linking time to export symbols from DLL. This feature can be specified at crosstool, package, target and command line level. A few differences from Unix platforms: 1. We don't build the shared library on Windows by default, users have to specifiy --output_groups=dynamic_library for building dynamic libraries. This output group is also available on other platforms. 2. By default, cc_test is dynamically linked on Unix, but it will be statically linked on Windows by default. (meaning the default value of linkstatic in cc_test is 1 on Windows, and 0 on other platforms) 3. For global data symbols, __declspec(dllimport) must still be used in source files. Remaining issues: 1. Extensions for import library and DLL are not correct yet. 2. DLLs are not guaranteed to be available during runtime yet. 3. Diamond problem If a cc_library A is specified as linkstatic=0, then no dynamic library will be built for it, so if another cc_library B depends on it, A will be statically linked into B, and if a cc_binary C depends on B, A will also be statically linked into C and B will be dynamically linked to C. This is wrong because A is duplicated in both B and C. It is essentially a diamond problem describled in C++ Transitive Library. (https://docs.google.com/document/d/1-tv0_79zGyBoDmaP_pYWaBVUwHUteLpAs90_rUl-VY8/edit?usp=sharing) Hopefully, we can avoid this by using cc_shared_library rule in future. Change-Id: I23640d4caf8afe65d60b1522af6368536d7a8408 PiperOrigin-RevId: 168829958
Diffstat (limited to 'tools/def_parser')
-rw-r--r--tools/def_parser/BUILD18
-rw-r--r--tools/def_parser/BUILD.tools13
-rw-r--r--tools/def_parser/no_op.bat17
3 files changed, 48 insertions, 0 deletions
diff --git a/tools/def_parser/BUILD b/tools/def_parser/BUILD
new file mode 100644
index 0000000000..7070bebf00
--- /dev/null
+++ b/tools/def_parser/BUILD
@@ -0,0 +1,18 @@
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+ name = "srcs",
+ srcs = glob(["**"]),
+)
+
+# cc_toolchain now implicitly depends on @bazel_tools//tools/def_parser:def_parser
+# We need to make sure @bazel_tools//tools/def_parser:def_parser is not
+# a cc_binary, because otherwise, we'll introduce a cycle in dependency graph:
+# .-> @bazel_tools//tools/def_parser:def_parser (cc_binary)
+# | cc_toolchain
+# `-- @bazel_tools//tools/def_parser:def_parser (cc_binary)
+
+filegroup(
+ name = "def_parser",
+ srcs = ["no_op.bat"],
+)
diff --git a/tools/def_parser/BUILD.tools b/tools/def_parser/BUILD.tools
new file mode 100644
index 0000000000..bd1b891fa8
--- /dev/null
+++ b/tools/def_parser/BUILD.tools
@@ -0,0 +1,13 @@
+package(default_visibility = ["//visibility:public"])
+
+filegroup(
+ name = "def_parser",
+ srcs = select({
+ "//src:host_windows": ["def_parser.exe"],
+ "//src:host_windows_msvc": ["def_parser.exe"],
+ "//src:host_windows_msys": ["def_parser.exe"],
+ "//conditions:default": [
+ "no_op.bat",
+ ],
+ }),
+)
diff --git a/tools/def_parser/no_op.bat b/tools/def_parser/no_op.bat
new file mode 100644
index 0000000000..b422585831
--- /dev/null
+++ b/tools/def_parser/no_op.bat
@@ -0,0 +1,17 @@
+:: Copyright 2016 The Bazel Authors. All rights reserved.
+::
+:: Licensed under the Apache License, Version 2.0 (the "License");
+:: you may not use this file except in compliance with the License.
+:: You may obtain a copy of the License at
+::
+:: http://www.apache.org/licenses/LICENSE-2.0
+::
+:: Unless required by applicable law or agreed to in writing, software
+:: distributed under the License is distributed on an "AS IS" BASIS,
+:: WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+:: See the License for the specific language governing permissions and
+:: limitations under the License.
+
+:: Invoke the python script under pydir with the same basename
+@echo OFF
+echo IGNORING: %0 %*