Commits on Jan 4, 2022

1. match: Properly align heapframes for CHERI/Arm's Morello prototype …

   On CHERI, and thus Arm's Morello prototype, pointers are represented as
   hardware capabilities, which consist of both an integer address and
   additional metadata, meaning they are twice the size of the platform's
   size_t type, i.e. 16 bytes on a 64-bit system. The ovector member of
   heapframe happens to only be 8 byte aligned, and so computing frame_size
   ends up with a multiple of 8 but not 16. Whilst the first frame is
   always suitably aligned, this then misaligns the frame that follows it,
   resulting in an alignment fault when storing a pointer to Fecode at the
   start of match.
   
   Thus, round up frame_size to a multiple of heapframe's alignment to
   ensure alignment is preserved. This can be completely optimised away on
   traditional architectures and, since CHERI's capabilities are in fact
   2 * sizeof(PCRE2_SIZE) bytes in size, the variable part of the
   expression is also proven to be a multiple of the alignment and so the
   aligning gets folded into the offsetof part by adding an additional 8,
   so no dynamic alignment code is needed even on CHERI architectures.

   

   jrtc27 committed Jan 4, 2022
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