diff options
author | Yun Peng <pcloudy@google.com> | 2017-09-15 15:59:14 +0200 |
---|---|---|
committer | László Csomor <laszlocsomor@google.com> | 2017-09-18 11:25:37 +0200 |
commit | 394211bf88b88c25036429e99894fa7c60eaaace (patch) | |
tree | a5a99354a9f3b8530bb0d98d61d8844b21348ecd /tools/def_parser | |
parent | f8480fac37692083b2f9c4e69b9b9e9e2c9b1853 (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/BUILD | 18 | ||||
-rw-r--r-- | tools/def_parser/BUILD.tools | 13 | ||||
-rw-r--r-- | tools/def_parser/no_op.bat | 17 |
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 %* |