[all-commits] [llvm/llvm-project] 895a72: [lld/mac] Support writing zippered dylibs and bundles

[Nico Weber via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 895a72111b0f1b6b29683d254dae4ebda9081eb4
      https://github.com/llvm/llvm-project/commit/895a72111b0f1b6b29683d254dae4ebda9081eb4
  Author: Nico Weber <thakis at chromium.org>
  Date:   2022-05-04 (Wed, 04 May 2022)

  Changed paths:
    M lld/MachO/Config.h
    M lld/MachO/Driver.cpp
    M lld/MachO/Writer.cpp
    M lld/test/MachO/platform-version.s
    M lld/test/MachO/zippered.yaml

  Log Message:
  -----------
  [lld/mac] Support writing zippered dylibs and bundles

With -platform_version flags for two distinct platforms,
this writes a LC_BUILD_VERSION header for each.

The motivation is that this is needed for self-hosting with lld as linker
after D124059.

To create a zippered output at the clang driver level, pass

    -target arm64-apple-macos -darwin-target-variant arm64-apple-ios-macabi

to create a zippered dylib.

(In Xcode's clang, `-darwin-target-variant` is spelled just `-target-variant`.)

(If you pass `-target arm64-apple-ios-macabi -target-variant arm64-apple-macos`
instead, ld64 crashes!)

This results in two -platform_version flags being passed to the linker.

ld64 also verifies that the iOS SDK version is at least 13.1. We don't do that
yet. But ld64 also does that for other platforms and we don't. So we need to
do that at some point, but not in this patch.

Only dylib and bundle outputs can be zippered.

I verified that a Catalyst app linked against a dylib created with

    clang -shared foo.cc -o libfoo.dylib \
          -target arm64-apple-macos \
          -target-variant arm64-apple-ios-macabi \
          -Wl,-install_name, at rpath/libfoo.dylib \
          -fuse-ld=$PWD/out/gn/bin/ld64.lld

runs successfully. (The app calls a function `f()` in libfoo.dylib
that returns a const char* "foo", and NSLog(@"%s")s it.)

ld64 is a bit more permissive when writing zippered outputs,
see references to "unzippered twins". That's not implemented yet.
(If anybody wants to implement that, D124275 is a good start.)

Differential Revision: https://reviews.llvm.org/D124887