[PATCH] elf: Restore how vDSO dependency is printed with LD_TRACE_LOADED_OBJECTS (BZ #29539)

[Adhemerval Zanella]

The d7703d3176d225d5743b21811d888619eba39e82 changed how vDSO like
dependencies are printed, instead of just the name and address it
follows other libraries mode and prints 'name => path'.

Unfortunately, this broke some ldd consumer that uses the output to
filter out the program's dependencies.  For instance CMake
bundleutilities module [1], where GetPrequirite uses the regex to filter
out 'name => path' [2].

This patch restore the previous way to print just the name and the
mapping address.

Checked on x86_64-linux-gnu.

[1] https://github.com/Kitware/CMake/tree/master/Tests/BundleUtilities
[2] https://github.com/Kitware/CMake/blob/master/Modules/GetPrerequisites.cmake#L733
---
 elf/rtld.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/elf/rtld.c b/elf/rtld.c
index cbbaf4a331..3e771a93d8 100644
--- a/elf/rtld.c
+++ b/elf/rtld.c
@@ -2122,6 +2122,12 @@ dl_main (const ElfW(Phdr) *phdr,
 	    if (l->l_faked)
 	      /* The library was not found.  */
 	      _dl_printf ("\t%s => not found\n",  l->l_libname->name);
+	    else if (strcmp (l->l_libname->name, l->l_name) == 0)
+	      /* Print vDSO like libraries without duplicate name.  Some
+		 consumers depend of this format.  */
+	      _dl_printf ("\t%s (0x%0*Zx)\n", l->l_libname->name,
+			  (int) sizeof l->l_map_start * 2,
+			  (size_t) l->l_map_start);
 	    else
 	      _dl_printf ("\t%s => %s (0x%0*Zx)\n",
 			  DSO_FILENAME (l->l_libname->name),
-- 
2.34.1