kc3-lang/SDL/src/cpuinfo

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• Hash : 02daab87
  Author :
  Date : 2021-07-29T18:09:38
  

  Fix pointer provenance in SDL_SIMDRealloc
  
  This is needed to support CHERI, and thus Arm's experimental Morello
  prototype, where pointers are implemented using unforgeable capabilities
  that include bounds and permissions metadata to provide fine-grained
  spatial and referential memory safety, as well as revocation by sweeping
  memory to provide heap temporal memory safety.
  
  The C standard does not guarantee that if two pointers compare equal
  they are the same pointer, as C pointers have a notion of provenance,
  and compilers have been known to exploit this during optimisation. For
  CHERI, this becomes even more important, as in-place expansion can
  result in realloc returning a capability to the same address but with
  increased capability bounds, and so reusing the old capability will trap
  trying to access outside the bounds of the original allocation.
  
  In the case that ptr == mem, memdiff and ptrdiff should still be equal,
  so the only overhead is a small amount of pointer arithmetic and a store
  of the new pointer (which is required per the C standard in order to not
  be undefined behaviour when next loaded).
  
  This also fixes the calculation of oldmem to use uintptr_t rather than
  size_t as casting the pointer to size_t on CHERI will strip the
  capability metadata, including the validity tag, with the subsequent
  cast back to void * resulting in a null-derived capability whose
  validity tag is clear and thus cannot be dereferenced without trapping.
  

• Files

• SDL_cpuinfo.c

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