[4.2] [runtime] Backwards-deployment support for class_getImageName #18076
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…ss_getImageName [runtime] Backwards-deployment support for class_getImageName https://bugs.swift.org/browse/SR-1917 rdar://problem/41535552 (cherry picked from commit 6f42fcc)
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@swift-ci Please test |
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Explanation: Follow-up to [4.2] Override ObjC's class_getImageName to handle Swift classes #17930. The hook for adding capabilities to
class_getImageNameis only present on new builds of the 2018 Apple OSs. That means we need a different answer on older OSs, and the best one we came up with (mostly @gparker42) is to overwrite symbol tables directly, to substitute in our implementation ofclass_getImageName.Scope: Sets up the new dyld image loading hook on all OSs that don't have the new
objc_setHook_getImageName. Also undoes the change to link arclite more often, since the feature we thought we'd need there is now just in the Swift runtime itself.Issue: SR-1917, rdar://problem/41535552
Risk: Medium. Patching symbol tables like this is a brazen idea, but it means that if we got something wrong we'd likely know about it immediately. The actual patched-in code is pretty straightforward.
Testing: Ran previously-added tests on iPhone, macOS, and iOS simulator environments with older OSs, verifying that the formerly XFAILing parts are now passisng.
Reviewed by: @mikeash, patching parts also reviewed by me (originally by @gparker42)