elf: Move ld.so error/help output to _dl_usage

Also add a comment to elf/Makefile, explaining why we cannot use
config.status for autoconf template processing.

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

elf/Makefile

@@ -59,7 +59,7 @@ elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \
 # ld.so uses those routines, plus some special stuff for being the program
 # interpreter and operating independent of libc.
 rtld-routines	= rtld $(all-dl-routines) dl-sysdep dl-environ dl-minimal \
-  dl-error-minimal dl-conflict dl-hwcaps
+  dl-error-minimal dl-conflict dl-hwcaps dl-usage
 all-rtld-routines = $(rtld-routines) $(sysdep-rtld-routines)
 
 CFLAGS-dl-runtime.c += -fexceptions -fasynchronous-unwind-tables
@@ -618,6 +618,12 @@ ldso_install: $(inst_rtlddir)/$(rtld-installed-name)
 endif
 
 
+# Workarounds for ${exec_prefix} expansion in configure variables.
+# config.status cannot be used directly for processing ldd.bash.in or
+# expanding variables such as sysconfdir because the expansion
+# contains the literal string ${exec_prefix}, which is not valid in C
+# headers or installed shell scripts.
+
 ldd-rewrite = -e 's%@RTLD@%$(rtlddir)/$(rtld-installed-name)%g' \
 	      -e 's%@VERSION@%$(version)%g' \
 	      -e 's|@PKGVERSION@|$(PKGVERSION)|g' \
@@ -655,6 +661,7 @@ libof-ldconfig = ldconfig
 CFLAGS-dl-cache.c += $(SYSCONF-FLAGS)
 CFLAGS-cache.c += $(SYSCONF-FLAGS)
 CFLAGS-rtld.c += $(SYSCONF-FLAGS)
+CFLAGS-dl-usage.c += $(SYSCONF-FLAGS)
 
 cpp-srcs-left := $(all-rtld-routines:=.os)
 lib := rtld

elf/dl-main.h

@@ -19,7 +19,9 @@
 #ifndef _DL_MAIN
 #define _DL_MAIN
 
+#include <ldsodefs.h>
 #include <limits.h>
+#include <stdlib.h>
 
 /* Length limits for names and paths, to protect the dynamic linker,
    particularly when __libc_enable_secure is active.  */
@@ -95,4 +97,7 @@ call_init_paths (const struct dl_main_state *state)
   _dl_init_paths (state->library_path);
 }
 
+/* Print ld.so usage information and exit.  */
+_Noreturn void _dl_usage (void) attribute_hidden;
+
 #endif /* _DL_MAIN */

elf/dl-usage.c

@@ -0,0 +1,51 @@
+/* Print usage information and help for ld.so.
+   Copyright (C) 1995-2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <dl-cache.h>
+#include <dl-main.h>
+#include <ldsodefs.h>
+
+void
+_dl_usage (void)
+{
+  _dl_fatal_printf ("\
+Usage: ld.so [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\
+loader to load the helper program from this file.  This helper program loads\n\
+the shared libraries needed by the program executable, prepares the program\n\
+to run, and runs it.  You may invoke this helper program directly from the\n\
+command line to load and run an ELF executable file; this is like executing\n\
+that file itself, but always uses this helper program from the file you\n\
+specified, instead of the helper program file specified in the executable\n\
+file you run.  This is mostly of use for maintainers to test new versions\n\
+of this helper program; chances are you did not intend to run this program.\n\
+\n\
+  --list                list all dependencies and how they are resolved\n\
+  --verify              verify that given object really is a dynamically linked\n\
+                        object we can handle\n\
+  --inhibit-cache       Do not use " LD_SO_CACHE "\n\
+  --library-path PATH   use given PATH instead of content of the environment\n\
+                        variable LD_LIBRARY_PATH\n\
+  --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names\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");
+}

elf/rtld.c

@@ -1246,31 +1246,7 @@ dl_main (const ElfW(Phdr) *phdr,
       /* If we have no further argument the program was called incorrectly.
 	 Grant the user some education.  */
       if (_dl_argc < 2)
-	_dl_fatal_printf ("\
-Usage: ld.so [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\
-loader to load the helper program from this file.  This helper program loads\n\
-the shared libraries needed by the program executable, prepares the program\n\
-to run, and runs it.  You may invoke this helper program directly from the\n\
-command line to load and run an ELF executable file; this is like executing\n\
-that file itself, but always uses this helper program from the file you\n\
-specified, instead of the helper program file specified in the executable\n\
-file you run.  This is mostly of use for maintainers to test new versions\n\
-of this helper program; chances are you did not intend to run this program.\n\
-\n\
-  --list                list all dependencies and how they are resolved\n\
-  --verify              verify that given object really is a dynamically linked\n\
-			object we can handle\n\
-  --inhibit-cache       Do not use " LD_SO_CACHE "\n\
-  --library-path PATH   use given PATH instead of content of the environment\n\
-			variable LD_LIBRARY_PATH\n\
-  --inhibit-rpath LIST  ignore RUNPATH and RPATH information in object names\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");
+	_dl_usage ();
 
       ++_dl_skip_args;
       --_dl_argc;