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Itanium Windows hot-patching replaced the first instruction bundle with a long branch

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

Itanium’s fixed-size instruction bundles let hot-patching replace the first bundle with a conditional long branch, without reserving spare space. The example shows how instruction-set details shape low-level update mechanisms.

What

Itanium Windows supported hot-patching by replacing a function's first instruction bundle with a long branch.

How

The branch accepts a 64-bit target and fits in the bundle as a double-wide instruction; no spare hot-patch space was needed.

Why it matters

The fixed bundle format explains how this hot-patching method could redirect execution without adding padding before functions.

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