| commit | 13affd7298c436a4b725a979fae876888ff6acb6 | [log] [tgz] |
|---|---|---|
| author | Googler <plf@google.com> | Fri Oct 14 06:05:43 2022 -0700 |
| committer | Copybara-Service <copybara-worker@google.com> | Fri Oct 14 06:07:17 2022 -0700 |
| tree | ef9efebc082f748c232ab46f62568f814079ee16 | |
| parent | 4779553eb5814025a465ebadbbced5c158996660 [diff] |
Add empty linker_input object in Starlark cc_library
This was a difference between the native implementation of cc_library and its Starlark counter part. The linker_input objects are propagated via the linking_context in the CcInfo provider. Each linker_input object contains an owner; the owner is represented by the label of the target creating the linker_input.
In the case of native cc_library, even if a target didn't add any new user_link_flags, files or object files, it still created a linker_input object while Starlark cc_library didn't. An example target that wouldn't create an empty linker_input object in the Starlark implementation would be:
cc_libary(
name = "foo",
deps = [
":bar",
":baz",
]
)
At the same time, the cc_shared_library logic would use the owners that it would see in the graph to make conclusions about what to link where. The Starlark implementation of cc_library would cause problems in the following case (using foo from above):
cc_shared_library(
name = "foo_shared",
roots = [":foo"],
static_deps = [ # This attribute is irrelevant for this problem.
"//..."
]
)
cc_binary(
name = "main",
srcs = ["main.cc"],
dynamic_deps = [":foo_shared"],
deps = [":foo"]
)
Since foo (a root is considered an export) doesn't create a linker_input, we don't detect it here and prune its subtree: https://cs.opensource.google/bazel/bazel/+/master:src/main/starlark/builtins_bzl/common/cc/experimental_cc_shared_library.bzl;drc=ff927f72644b4d1c3036ea8b3b821c58c34c92fa;l=89. That's because it's not added to the can_be_linked_dynamically dictionary here: https://cs.opensource.google/bazel/bazel/+/master:src/main/starlark/builtins_bzl/common/cc/experimental_cc_shared_library.bzl;drc=ff927f72644b4d1c3036ea8b3b821c58c34c92fa;l=258
Therefore,if experimental_link_static_libraries_once is off (which is the case for Tensorflow) the algorithm in cc_shared_library deciding what to link into the cc_binary will link bar and baz again into the binary even though they were already linked into foo_shared. The error would have been caught earlier if the flag experimental_link_static_libraries_once had been True but the right behavior is not to attempt to link bar and baz into the binary since these targets are not reachable without going through a library that was exported by a shared library (i.e. the library foo which we didn't detect).
Fixes #16296
RELNOTES:none
PiperOrigin-RevId: 481127757
Change-Id: Ieb4a98002cc77ff751a9ae15773998aab350ece6
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