elf: Implement ld.so --help

--help processing is deferred to the point where the executable has
been loaded, so that it is possible to eventually include information
from the main executable in the help output.

As suggested in the GNU command-line interface guidelines, the help
message is printed to standard output, and the exit status is
successful.

Handle usage errors closer to the GNU command-line interface
guidelines.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

1 files changed, 20 insertions, 4 deletions

diff --git a/elf/dl-usage.c b/elf/dl-usage.c
index f3d89d22b7..c1820dca2f 100644
--- a/elf/dl-usage.c
+++ b/elf/dl-usage.c
@@ -19,12 +19,24 @@
 #include <dl-cache.h>
 #include <dl-main.h>
 #include <ldsodefs.h>
+#include <unistd.h>
 
 void
-_dl_usage (void)
+_dl_usage (const char *argv0, const char *wrong_option)
 {
-  _dl_fatal_printf ("\
-Usage: ld.so [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
+  if (wrong_option != NULL)
+    _dl_error_printf ("%s: unrecognized option '%s'\n", argv0, wrong_option);
+  else
+    _dl_error_printf ("%s: missing program name\n", argv0);
+  _dl_error_printf ("Try '%s --help' for more information.\n", argv0);
+  _exit (EXIT_FAILURE);
+}
+
+void
+_dl_help (const char *argv0, struct dl_main_state *state)
+{
+  _dl_printf ("\
+Usage: %s [OPTION]... EXECUTABLE-FILE [ARGS-FOR-PROGRAM...]\n\
 You have invoked `ld.so', the helper program for shared library executables.\n\
 This program usually lives in the file `/lib/ld.so', and special directives\n\
 in executable files using ELF shared libraries tell the system's program\n\
@@ -47,5 +59,9 @@ of this helper program; chances are you did not intend to run this program.\n\
                         in LIST\n\
   --audit LIST          use objects named in LIST as auditors\n\
   --preload LIST        preload objects named in LIST\n\
-  --argv0 STRING        set argv[0] to STRING before running\n");
+  --argv0 STRING        set argv[0] to STRING before running\n\
+  --help                display this help and exit\n\
+",
+              argv0);
+  _exit (EXIT_SUCCESS);
 }