ld.so: Support moving versioned symbols between sonames [BZ #24741]

This change should be fully backwards-compatible because the old
code aborted the load if a soname mismatch was encountered
(instead of searching further for a matching symbol).  This means
that no different symbols are found.

The soname check was explicitly disabled for the skip_map != NULL
case.  However, this only happens with dl(v)sym and RTLD_NEXT,
and those lookups do not come with a verneed entry that could be used
for the check.

The error check was already explicitly disabled for the skip_map !=
NULL case, that is, when dl(v)sym was called with RTLD_NEXT.  But
_dl_vsym always sets filename in the struct r_found_version argument
to NULL, so the check was not active anyway.  This means that
symbol lookup results for the skip_map != NULL case do not change,
either.

1 files changed, 6 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 650b81a2e7..6c7de105ac 100644
--- a/NEWS
+++ b/NEWS
@@ -34,6 +34,12 @@ Major new features:
   pointer subtraction within the allocated object, where results might
   overflow the ptrdiff_t type.
 
+* The dynamic linker no longer refuses to load objects which reference
+  versioned symbols whose implementation has moved to a different soname
+  since the object has been linked.  The old error message, symbol
+  FUNCTION-NAME, version SYMBOL-VERSION not defined in file DSO-NAME with
+  link time reference, is gone.
+
 Deprecated and removed features, and other changes affecting compatibility:
 
 * The copy_file_range function fails with ENOSYS if the kernel does not