Re: A Famous Security Bug

On 2024-03-22, James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

And the C standard imposes no requirement that such behavior occur as
described by the abstract semantics. Only actual observable behavior, as
that term is defined by the C standard, must occur as if those semantics
were followed - whether or not they actually were.

But there is something. Though not normative text, EXAMPLE 1 gives
the range of possibilities for optimization:

  EXAMPLE 1 An implementation might define a one-to-one correspondence
  between abstract and actual semantics: at every sequence point, the
  values of the actual objects would agree with those specified by the
  abstract semantics. The keyword volatile would then be redundant.

  Alternatively, an implementation might perform various optimizations
  within each translation unit, such that the actual semantics would agree
  with the abstract semantics only when making function calls across
  translation unit boundaries.

I believe the intent of this example is to give the two extremes
representing the full range of what is envisioned as permissible.

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