[5.0] Future-proof the ARM64 ABI by not reserving the entire top byte #21474
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Targets that want to use armv8.5a memory tagging will need this. Hopefully nobody comes up with a brilliant reason they need to use anything else.
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Please test with following pull request: @swift-ci please test |
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@AnnaZaks this is now failing for a different reason: |
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AnnaZaks
approved these changes
Dec 21, 2018
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Targets that want to use armv8.5a memory tagging will need this. Hopefully nobody comes up with a brilliant reason they need to use anything else.
I considered whether to push this to other 64-bit targets and decided that it was pretty architecture-specific. If somehow x86-64 adds a similar feature, there's no reason to think it'll look exactly the same down to the range of bits it claims. (Intel is probably also less likely to be willing to sacrifice address space, whereas ARM already made that decision due to TBI.)
This is the 5.0 version of #21453, which means it is a re-submission of #21015, the 5.0 version of #21000. It is contingent on a fix to
Stringto no longer assume that that it can use the entire top 8 bits (master #21310, 5.0 #21392) and a corresponding fix to LLDB (master apple/swift-lldb#1168, 5.0 apple/swift-lldb#1169).This is ABI-affecting.