commit ea85e7d55087075376a29261e722e4fae14ecbe7
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Jul 4 21:46:30 2025 +0200

    elf: Restore support for _r_debug interpositions and copy relocations
    
    The changes in commit a93d9e03a31ec14405cb3a09aa95413b67067380
    ("Extend struct r_debug to support multiple namespaces [BZ #15971]")
    break the dyninst dynamic instrumentation tool.  It brings its
    own definition of _r_debug (rather than a declaration).
    
    Furthermore, it turns out it is rather hard to use the proposed
    handshake for accessing _r_debug via DT_DEBUG. If applications want
    to access _r_debug, they can do so directly if the relevant code has
    been built as PIC.  To protect against harm from accidental copy
    relocations due to linker relaxations, this commit restores copy
    relocation support by adjusting both copies if interposition or
    copy relocations are in play.  Therefore, it is possible to
    use a hidden reference in ld.so to access _r_debug.
    
    Only perform the copy relocation initialization if libc has been
    loaded.  Otherwise, the ld.so search scope can be empty, and the
    lookup of the _r_debug symbol mail fail.
    
    Reviewed-by: H.J. Lu <hjl.tools@gmail.com>

commit a93d9e03a31ec14405cb3a09aa95413b67067380
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Tue Aug 17 19:35:48 2021 -0700

    Extend struct r_debug to support multiple namespaces [BZ #15971]
    
    Glibc does not provide an interface for debugger to access libraries
    loaded in multiple namespaces via dlmopen.
    
    The current rtld-debugger interface is described in the file:
    
    elf/rtld-debugger-interface.txt
    
    under the "Standard debugger interface" heading.  This interface only
    provides access to the first link-map (LM_ID_BASE).
    
    1. Bump r_version to 2 when multiple namespaces are used.  This triggers
    the GDB bug:
    
    https://sourceware.org/bugzilla/show_bug.cgi?id=28236
    
    2. Add struct r_debug_extended to extend struct r_debug into a linked-list,
    where each element correlates to an unique namespace.
    3. Initialize the r_debug_extended structure.  Bump r_version to 2 for
    the new namespace and add the new namespace to the namespace linked list.
    4. Add _dl_debug_update to return the address of struct r_debug' of a
    namespace.
    5. Add a hidden symbol, _r_debug_extended, for struct r_debug_extended.
    6. Provide the symbol, _r_debug, with size of struct r_debug, as an alias
    of _r_debug_extended, for programs which reference _r_debug.
    
    This fixes BZ #15971.
    
    Reviewed-by: Florian Weimer <fweimer@redhat.com>