[llvm-bugs] [Bug 40120] New: thread_local variables are not aligned properly on NetBSD

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=40120

            Bug ID: 40120
           Summary: thread_local variables are not aligned properly on
                    NetBSD
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: -New Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: mgorny at gentoo.org
                CC: htmldeveloper at gmail.com, llvm-bugs at lists.llvm.org,
                    neeilans at live.com, richard-llvm at metafoo.co.uk

Demonstration program:

  #include <cstdio>

  struct alignas(64) a {
    int x;
  };

  void b() {
    thread_local a as_tls;

    printf("as tls: %p\n", &as_tls);
  }

  int main() {
    b();
    return 0;
  }

The result is:

  as tls: 0x7f7ff7efe068

which is clearly not aligned properly.  However, clang/llvm seems to assume the
alignment will take place and generates MOVAPS instructions that segfault due
to wrong alignment.

FWIU, this is a bug in NetBSD ld.so but it's not expected to be fixed anytime
soon.  Is there any chance for a short-term solution that would e.g. add make
LLVM take more TLS space and round the returned address to obtain necessary
alignment?

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