Windows on AArch64 also provides for hot-patching, but it’s much simpler than on x86

This article discusses how Windows on AArch64 implements hot-patching with simpler mechanics compared to x86 due to its fixed-length instruction set. It explains the use of patch points and the atomicity of instruction updates.

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I have noted in the past that x86-32 and x86-64 versions of Windows are careful to start each function with a patch point. But what about AArch64 (known in Windows as arm64)?

Windows also inserts patch points for functions on AArch64, but they are much simpler due to the fixed-length instruction set. You don’t have to worry about patching an instruction when the instruction pointer happens to be in the middle of the byte sequence, because the instruction pointer is never in the middle of the byte sequence. The instruction pointer is always on a multiple of 4.

Therefore, there is no special restriction on the first instruction of a function. All instructions meet the requirements of being atomically updatable without risk of the instruction pointer being in the middle of the instruction.

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