http://sourceware.org/ml/gdb-patches/2010-03/msg01000.html
Subject: [patch 2/6] PIE: Attach binary even after ld.so re-prelinked  underneath

Hi,

when I have seen the PIE-binary-changed-sice-start tested also
ld.so-changed-since-start and it did not work.

There is questionable when to print and when to not to print non-fatal memory
read errors.  Similar change I requested in
	Re: [RFC/ia64] memory error when reading wrong core file
	http://sourceware.org/ml/gdb-patches/2010-02/msg00001.html
so that GDB prints at least as a warning
	Cannot access memory at address ...
when some unexpected error happens.

Contrary to it there is not such warning present in the code below as in the
case of non-valgrind PIE with re-prelinked ld.so the memory read error happens
there.  Some GDB code rework could probably avoid it.

Just for example all the memory read errors in read_program_header or even
- primarily - scan_dyntag are currently IMO-incorrectly silent and others.
Therefore posted the patch this way, making all these warnings printed and
possibly fixing code attempting incorrect reads along the way could be done by
a different patch.

No regressions on {x86_64,x86_64-m32,i686}-fedora12-linux-gnu for the whole
patch series together.


Thanks,
Jan


gdb/
2010-03-29  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* auxv.c (ld_so_xfer_auxv): Do not error on failed read of data_address.

gdb/testsuite/
2010-03-29  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.base/break-interp.exp (test_attach): Keep $interp changed.  Move
	its restore after the <$relink_args != ""> loop.  new comment.

--- a/gdb/auxv.c
+++ b/gdb/auxv.c
@@ -96,7 +96,16 @@ ld_so_xfer_auxv (gdb_byte *readbuf,
 
   pointer_address = SYMBOL_VALUE_ADDRESS (msym);
 
-  data_address = read_memory_typed_address (pointer_address, ptr_type);
+  /* While it is an error I am not aware how to solve attaching to PIE under
+     valgrind --db-attach=yes different way when ld.so on-disk file has prelink
+     change in the meantime.  Currently GDB will drop back to procfs_xfer_auxv
+     (so that at least non-valgrind PIE attachments with prelink change of
+     ld.so work).  To make it working even with valgrind is PR 11440 requiring
+     a valgrind extension.  */
+  if (target_read_memory (pointer_address, ptr_buf, ptr_size) != 0)
+    return -1;
+
+  data_address = extract_typed_address (ptr_buf, ptr_type);
 
   /* Possibly still not initialized such as during an inferior startup.  */
   if (data_address == 0)
--- a/gdb/testsuite/gdb.base/break-interp.exp
+++ b/gdb/testsuite/gdb.base/break-interp.exp
@@ -419,12 +419,16 @@ proc test_attach {file displacement {relink_args ""}} {
 	global exec interp_saved interp
 
 	foreach relink {YES NO} {
-	    if {[prelink$relink $relink_args [file tail $exec]]
-	        && [copy $interp_saved $interp]} {
+	    # It would be more correct to also [copy $interp_saved $interp]
+	    # here to really test just different prelink of $exec.
+	    # But we would need a separate test for different prelink of ld.so
+	    # where a bug occured.  It is now all merged into this single test.
+	    if [prelink$relink $relink_args [file tail $exec]] {
 		# /proc/PID/exe cannot be loaded as it is "EXECNAME (deleted)".
 		test_attach_gdb $exec $pid $displacement "attach-relink$relink"
 	    }
 	}
+	copy $interp_saved $interp
     }
 
     remote_exec host "kill -9 $pid"