as: AArch64 Mapping Symbols

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1 9.1.7 Mapping Symbols
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1 The AArch64 ELF specification requires that special symbols be inserted
1 into object files to mark certain features:
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1 '$x'
1      At the start of a region of code containing AArch64 instructions.
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1 '$d'
1      At the start of a region of data.
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