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>

1 files changed, 8 insertions, 4 deletions

diff --git a/sysdeps/generic/ldsodefs.h b/sysdeps/generic/ldsodefs.h
index fd67871f4b..6e50fcd7cd 100644
--- a/sysdeps/generic/ldsodefs.h
+++ b/sysdeps/generic/ldsodefs.h
@@ -355,7 +355,7 @@ struct rtld_global
       void (*free) (void *);
     } _ns_unique_sym_table;
     /* Keep track of changes to each namespace' list.  */
-    struct r_debug _ns_debug;
+    struct r_debug_extended _ns_debug;
   } _dl_ns[DL_NNS];
   /* One higher than index of last used namespace.  */
   EXTERN size_t _dl_nns;
@@ -1099,12 +1099,16 @@ extern void _dl_sort_maps (struct link_map **maps, unsigned int nmaps,
 extern void _dl_debug_state (void);
 rtld_hidden_proto (_dl_debug_state)
 
-/* Initialize `struct r_debug' if it has not already been done.  The
-   argument is the run-time load address of the dynamic linker, to be put
-   in the `r_ldbase' member.  Returns the address of the structure.  */
+/* Initialize `struct r_debug_extended' for the namespace NS.  LDBASE
+   is the run-time load address of the dynamic linker, to be put in the
+   `r_ldbase' member.  Return the address of the structure.  */
 extern struct r_debug *_dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
      attribute_hidden;
 
+/* Update the `r_map' member and return the address of `struct r_debug'
+   of the namespace NS.  */
+extern struct r_debug *_dl_debug_update (Lmid_t ns) attribute_hidden;
+
 /* Initialize the basic data structure for the search paths.  SOURCE
    is either "LD_LIBRARY_PATH" or "--library-path".
    GLIBC_HWCAPS_PREPEND adds additional glibc-hwcaps subdirectories to