Future-proof the ARM64 ABI by not reserving the entire top byte #21453
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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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@swift-ci Please test. |
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Build failed |
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Build failed |
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@swift-ci Please clean test. |
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Both test-suite failures were LLDB failures involving |
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@swift-ci Please test. |
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Apparently my latest test run might have just not included apple/swift-lldb#1168. |
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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 a re-submission of #21000 now that
Stringis no longer assuming that it can use the entire top 8 bits (#21310). I've also added a test that the behavior changes on ARM64.