[PATCH] D142410: [AArch64] ARMv8.5-A implies both FEAT_SB and FEAT_SSBS

Tue Jan 24 02:58:06 PST 2023

lenary added a comment.

In D142410#4076389 <https://reviews.llvm.org/D142410#4076389>, @philipp.tomsich wrote:

> When looking at "ARM DDI 0487G.a", on page A2-68 under the heading "Additional functionality added to Armv8.0 in later releases" in the definition-list item "FEAT_SSBS, Speculative Store Bypass Safe":
>
>> This feature is OPTIONAL in Armv8.0 implementations and mandatory in Armv8.5 implementations.
>
> There is a to FEAT_SBSS in the backlink in "A2.8 The Armv8.5 architecture extension", under the subsection "A2.8.3 Features added to earlier extensions", in the bullet-list labeled "The features that have been added to earlier architectural extensions are:"

I cited version `I.a`, which is later than version `G.a`. Looking at the errata for version `G.b`, erratum R18653 (page 93) is where it was relaxed to not be mandatory from v8.5a. Errata document link: https://developer.arm.com/documentation/102105/gb-05/?lang=en (I'm just happy this was in the first errata document I looked for!)

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