[PATCH] D110869: [X86] Implement -fzero-call-used-regs option

[James Y Knight via Phabricator via llvm-commits]

jyknight added inline comments.


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Comment at: clang/include/clang/Basic/AttrDocs.td:6271
+This attribute, when attached to a function, causes the compiler to zero a
+subset of all call-used registers before the function returns. It's used to
+increase program security by either mitigating `Return-Oriented Programming`_
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I think we need to define "call-used" here. It's not a very common name for this concept, and it's especially confusing because of the double-use of the word "used". I was really confused by the definition of the "all" choice when first reading it -- thinking "Wait, 'all' also only clears the registers which were used? How's that different than 'used', then? Ooooohhhh, 'call-used' doesn't mean it IS USED in the call, only that it's not guaranteed to be PRESERVED."

Suggestion for text:
The term "call-used" means registers which are not guaranteed to be preserved unchanged for the caller by the current calling convention. This could also be described as "caller-saved" or "not callee-saved".




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https://reviews.llvm.org/D110869