[all-commits] [llvm/llvm-project] 108ab4: [Clang] Disable use of the counted_by attribute fo...

[Bill Wendling via All-commits]

  Branch: refs/heads/release/19.x
  Home:   https://github.com/llvm/llvm-project
  Commit: 108ab46cf57d769795c8310cebcf73e3a0c189ad
      https://github.com/llvm/llvm-project/commit/108ab46cf57d769795c8310cebcf73e3a0c189ad
  Author: Bill Wendling <morbo at google.com>
  Date:   2024-10-29 (Tue, 29 Oct 2024)

  Changed paths:
    M clang/lib/CodeGen/CGBuiltin.cpp
    M clang/test/CodeGen/attr-counted-by.c

  Log Message:
  -----------
  [Clang] Disable use of the counted_by attribute for whole struct pointers (#112636)

The whole struct is specificed in the __bdos. The calculation of the
whole size of the structure can be done in two ways:

    1) sizeof(struct S) + count * sizeof(typeof(fam))
    2) offsetof(struct S, fam) + count * sizeof(typeof(fam))

The first will add any remaining whitespace that might exist after
allocation while the second method is more precise, but not quite
expected from programmers. See [1] for a discussion of the topic.

GCC isn't (currently) able to calculate __bdos on a pointer to the whole
structure. Therefore, because of the above issue, we'll choose to match
what GCC does for consistency's sake.

[1] https://lore.kernel.org/lkml/ZvV6X5FPBBW7CO1f@archlinux/

Co-authored-by: Eli Friedman <efriedma at quicinc.com>



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