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Windows uses a three-instruction trampoline for AArch64 hot-patching

devblogs.microsoft.com by Raymond Chen Editor score 7/10

Windows reserves 12 bytes before each AArch64 function for a three-instruction trampoline, then redirects the function entry with a branch. The fixed-length instruction set simplifies safe patch-point design.

What: • Windows on AArch64 reserves a 12-byte patch space before each function for hot-patching.
How: • A three-instruction trampoline branches from the function entry point to the patch space, then redirects execution to the replacement.
Why it matters: • Fixed-length AArch64 instructions keep the instruction pointer on 4-byte boundaries, allowing atomic instruction updates without risk of landing mid-instruction.

The function entry point branches to a three-instruction patch-space trampoline that redirects to the replacement. Sketched from the article's own text.

Read on devblogs.microsoft.com →

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