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Add opt-out from merging cc_lib object files in bindgen #2959

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Add opt-out from merging cc_lib object files in bindgen #2959

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Commits on Oct 24, 2024

  1. Add opt-out from merging cc_lib object files in bindgen 

    This is a ~rollback of
bazelbuild#2590, as it turns out the
current behavior is incomatible with
https://bazel.build/docs/user-manual#dynamic-mode (which is very hard to
use in the OSS because of
bazelbuild/bazel#4135).

In short, the dynamic mode works as follows:

* Each cc_library produces object files that are used to produce
    * a static library (often not materialized but objects get passed as
      `--start-lib`/`--end-lib` to the linker),
    * a shared library (only
      containing the objects, not transitive dependencies),
    * and an interface library (produced from .so by "stripping function
      bodies").
* When linking binaries, by default we use the static linking.
* When linking tests, by default we use interface libraries for linking,
  and shared libraries for test execution.

The motivation for this is to avoid lengthy linking actions when all
that has changed between previous build is the method body (therefore
Bazel produces the same interface library, so we don't need to reexecute
linking action).

We do not support dynamic mode in rules_rust yet.

The current bindgen behavior works by taking object from `cc_lib`, and
merging them into the `rlib` output. When dynamic_mode is on, we now
have a linking action that has the rlib early on the command line, and then
interface libraries of dependencies of the `cc_lib`, and then the interface library of the `cc_lib`. For reasons,
lld prefers statically defined symbols, it sees that the `rlib` defines the same symbols as `cc_lib` but statically, and errors
out with `backward reference detected`, even though `cc_lib` is
positioned correctly.

The fix for us is to not merge objects.
    @hlopko
    hlopko committed Oct 24, 2024
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  2. Regenerate documentation

    @hlopko
    hlopko committed Oct 24, 2024
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