Correct a bug when remapping textrel segments on nommu

From: Alan Davis <adavis@ti.com>

On C6X, when trying to execute a program that has a textrel DSO, it
fails to load. The telltale line in the LD_DEBUG output is:

_dl_get_ready_to_run:779:       file='';  needed by './a.out'

The corresponding DT_NEEDED entry has 'libc.so.0', but here the
filename is empty. This is what is happening in
_dl_elf_shared_library():

First, map all segments according to their permissions. Text gets
initially mapped read-only.

Then, parse the dynamic information. The dynamic table is in RW but
some of the tags may point to RO. For example, DT_NEEDED points to a
string in .dynstr which is in RO. These pointers get computed
according to the loadmap from the original mapping.

Then, in response to a DT_TEXTREL tag, the RO segment gets remapped,
thereby invaliding anything that points to it, in particular certain
dynamic tags such as DT_NEEDED.

The following patch re-parses the dynamic info after the remapping so
as to re-compute any invalid pointers.

Signed-off-by: Alan Davis <adavis@ti.com>
Signed-off-by: Bernd Schmidt <bernds@codesourcery.com>

ldso/ldso/dl-elf.c

@@ -714,6 +714,9 @@ struct elf_resolve *_dl_load_elf_shared_library(int secure,
 				DL_UPDATE_LOADADDR_HDR(lib_loadaddr,
 						       new_addr + (ppnt->p_vaddr & ADDR_ALIGN),
 						       ppnt);
+				/* This has invalidated all pointers into the previously readonly segment.
+				   Update any them to point into the remapped segment.  */
+				_dl_parse_dynamic_info(dpnt, dynamic_info, NULL, lib_loadaddr);
 #endif
 			}
 		}