New subject: [Bug 57700] NTDLL under-aligns implicit module TLS

20 Jan 2025

      https://bugs.winehq.org/show_bug.cgi?id=57700

            Bug ID: 57700
           Summary: NTDLL under-aligns implicit module TLS
           Product: Wine
           Version: 10.0-rc6
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ntdll
          Assignee: wine-bugs(a)winehq.org
          Reporter: me(a)purplesyringa.moe
      Distribution: ---

Created attachment 77888
  --> https://bugs.winehq.org/attachment.cgi?id=77888
Reproducer

alloc_tls_slot in dlls/ntdll/loader.c spells:

    if (!(new_ptr = RtlAllocateHeap( GetProcessHeap(), 0, size +
dir->SizeOfZeroFill ))) return -1;

This allocates the thread-local storage without an alignment. MSDN says that
the correct alignment is specified in the Characteristics field of the TLS
directory, which Wine promptly ignores.
(https://learn.microsoft.com/en-us/windows/win32/debug/pe-format#the-tls-dire...)
This leads to unsatisfied alignment requirements in programs that expect it,
often leading to crashes, as seen in
https://github.com/rust-lang/rust/issues/135719.

For testing, I have attached a small example built with MSVC that allocates a
page-aligned thread local and prints its address. The compiled executable is at
https://mega.nz/file/AJhyVAyA#3JDbONv0-TIQPqLKpUW7zg9DLRjP9IqHsdOIpxUHSUs. The
alignment specified in the TLS directory is 4096, matching the source code, as
verified by `dumpbin /tls`.

If you'd like me to attach the executable to the ticket directly or need more
information, please do tell.

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[Bug 57700] New: NTDLL under-aligns implicit module TLS

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