Commits on Sep 24, 2024

1. bodies_by_type[SVt_PVNV]: handle __float128 NV alignment on 32-bit …

   Perl SV body structures include xmg_stash and xmg_u fields at the
   front, which are only valid for type SVt_PVMG and higher.
   
   This allows those fields to be at a constant offset from the start
   of the body.
   
   To save memory perl generally allocates the bodies where
   type < SVt_PVMG without the space needed for these two fields,
   offsetting the body pointer back by the size of the two fields.  At
   least for the first body in an arena this is technically
   undefined behaviour, but we've done it forever.
   
   With -msse __float128 requires 16 byte alignment, but for XPVNV
   bodies the hack used here means that the base of the XPVNV
   body ends up mis-aligned on 32-bit systems.
   
   On 64-bit systems the combined size of those fields is 16-bytes so
   the modified pointer is still properly aligned.
   
   To fix this allocate the full XPVNV structure when 16 byte alignment
   is required for NV, NV is more than 8 bytes and pointers are small
   enough that the NV would have been mis-aligned.
   
   Fixes Perl#22577

   

   tonycoz committed Sep 24, 2024
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