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, 5 insertions, 5 deletions

diff --git a/elf/dl-open.c b/elf/dl-open.c
index ec386626f9..a25443f6d1 100644
--- a/elf/dl-open.c
+++ b/elf/dl-open.c
@@ -574,7 +574,7 @@ dl_open_worker (void *a)
       if ((mode & RTLD_GLOBAL) && new->l_global == 0)
 	add_to_global_update (new);
 
-      assert (_dl_debug_initialize (0, args->nsid)->r_state == RT_CONSISTENT);
+      assert (_dl_debug_update (args->nsid)->r_state == RT_CONSISTENT);
 
       return;
     }
@@ -630,7 +630,7 @@ dl_open_worker (void *a)
 #endif
 
   /* Notify the debugger all new objects are now ready to go.  */
-  struct r_debug *r = _dl_debug_initialize (0, args->nsid);
+  struct r_debug *r = _dl_debug_update (args->nsid);
   r->r_state = RT_CONSISTENT;
   _dl_debug_state ();
   LIBC_PROBE (map_complete, 3, args->nsid, r, new);
@@ -830,7 +830,7 @@ no more namespaces available for dlmopen()"));
 	  ++GL(dl_nns);
 	}
 
-      _dl_debug_initialize (0, nsid)->r_state = RT_CONSISTENT;
+      _dl_debug_update (nsid)->r_state = RT_CONSISTENT;
     }
   /* Never allow loading a DSO in a namespace which is empty.  Such
      direct placements is only causing problems.  Also don't allow
@@ -899,7 +899,7 @@ no more namespaces available for dlmopen()"));
 	     the flag here.  */
 	}
 
-      assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);
+      assert (_dl_debug_update (args.nsid)->r_state == RT_CONSISTENT);
 
       /* Release the lock.  */
       __rtld_lock_unlock_recursive (GL(dl_load_lock));
@@ -908,7 +908,7 @@ no more namespaces available for dlmopen()"));
       _dl_signal_exception (errcode, &exception, NULL);
     }
 
-  assert (_dl_debug_initialize (0, args.nsid)->r_state == RT_CONSISTENT);
+  assert (_dl_debug_update (args.nsid)->r_state == RT_CONSISTENT);
 
   /* Release the lock.  */
   __rtld_lock_unlock_recursive (GL(dl_load_lock));