From e82d19822ee225e75c22d0362e34e970962adf89 Mon Sep 17 00:00:00 2001
From: Konstantin Belousov <kib@FreeBSD.org>
Date: Sun, 31 May 2020 22:37:33 +0000
Subject: [PATCH] rtld: Add -b option to allow to specify image name different
 from arg0.

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
---
 libexec/rtld-elf/rtld.1 | 14 +++++++++++++-
 libexec/rtld-elf/rtld.c | 32 +++++++++++++++++++++++++++-----
 2 files changed, 40 insertions(+), 6 deletions(-)

diff --git a/libexec/rtld-elf/rtld.1 b/libexec/rtld-elf/rtld.1
index 5eeb17a841bf..ed2ce96eac8f 100644
--- a/libexec/rtld-elf/rtld.1
+++ b/libexec/rtld-elf/rtld.1
@@ -28,7 +28,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 20, 2017
+.Dd June 1, 2020
 .Dt RTLD 1
 .Os
 .Sh NAME
@@ -302,6 +302,7 @@ Execution options may be specified.
 The syntax of the direct invocation is
 .Bd -ragged -offset indent
 .Pa /libexec/ld-elf.so.1
+.Op Fl b Ar exe
 .Op Fl f Ar fd
 .Op Fl p
 .Op Fl -
@@ -311,6 +312,17 @@ The syntax of the direct invocation is
 .Pp
 The options are:
 .Bl -tag -width indent
+.It Fl b Ar exe
+Use the executable
+.Fa exe
+instead of
+.Fa image_path
+for activation.
+If this option is specified,
+.Ar image_path
+is only used to provide the
+.Va argv[0]
+value to the program.
 .It Fl f Ar fd
 File descriptor
 .Ar fd
diff --git a/libexec/rtld-elf/rtld.c b/libexec/rtld-elf/rtld.c
index cf1110d47bd8..82376e85bc07 100644
--- a/libexec/rtld-elf/rtld.c
+++ b/libexec/rtld-elf/rtld.c
@@ -136,7 +136,8 @@ static void objlist_put_after(Objlist *, Obj_Entry *, Obj_Entry *);
 static void objlist_remove(Objlist *, Obj_Entry *);
 static int open_binary_fd(const char *argv0, bool search_in_path,
     const char **binpath_res);
-static int parse_args(char* argv[], int argc, bool *use_pathp, int *fdp);
+static int parse_args(char* argv[], int argc, bool *use_pathp, int *fdp,
+    const char **argv0);
 static int parse_integer(const char *);
 static void *path_enumerate(const char *, path_enum_proc, const char *, void *);
 static void print_usage(const char *argv0);
@@ -467,8 +468,7 @@ _rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
 	    }
 	    dbg("opening main program in direct exec mode");
 	    if (argc >= 2) {
-		rtld_argc = parse_args(argv, argc, &search_in_path, &fd);
-		argv0 = argv[rtld_argc];
+		rtld_argc = parse_args(argv, argc, &search_in_path, &fd, &argv0);
 		explicit_fd = (fd != -1);
 		binpath = NULL;
 		if (!explicit_fd)
@@ -5610,17 +5610,20 @@ open_binary_fd(const char *argv0, bool search_in_path,
  * Parse a set of command-line arguments.
  */
 static int
-parse_args(char* argv[], int argc, bool *use_pathp, int *fdp)
+parse_args(char* argv[], int argc, bool *use_pathp, int *fdp,
+    const char **argv0)
 {
 	const char *arg;
 	char machine[64];
 	size_t sz;
 	int arglen, fd, i, j, mib[2];
 	char opt;
+	bool seen_b, seen_f;
 
 	dbg("Parsing command-line arguments");
 	*use_pathp = false;
 	*fdp = -1;
+	seen_b = seen_f = false;
 
 	for (i = 1; i < argc; i++ ) {
 		arg = argv[i];
@@ -5647,7 +5650,21 @@ parse_args(char* argv[], int argc, bool *use_pathp, int *fdp)
 			if (opt == 'h') {
 				print_usage(argv[0]);
 				_exit(0);
+			} else if (opt == 'b') {
+				if (seen_f) {
+					_rtld_error("Both -b and -f specified");
+					rtld_die();
+				}
+				i++;
+				*argv0 = argv[i];
+				seen_b = true;
+				break;
 			} else if (opt == 'f') {
+				if (seen_b) {
+					_rtld_error("Both -b and -f specified");
+					rtld_die();
+				}
+
 				/*
 				 * -f XX can be used to specify a
 				 * descriptor for the binary named at
@@ -5671,6 +5688,7 @@ parse_args(char* argv[], int argc, bool *use_pathp, int *fdp)
 					rtld_die();
 				}
 				*fdp = fd;
+				seen_f = true;
 				break;
 			} else if (opt == 'p') {
 				*use_pathp = true;
@@ -5700,6 +5718,8 @@ parse_args(char* argv[], int argc, bool *use_pathp, int *fdp)
 		}
 	}
 
+	if (!seen_b)
+		*argv0 = argv[i];
 	return (i);
 }
 
@@ -5734,10 +5754,12 @@ static void
 print_usage(const char *argv0)
 {
 
-	rtld_printf("Usage: %s [-h] [-f <FD>] [-p] [--] <binary> [<args>]\n"
+	rtld_printf(
+	    "Usage: %s [-h] [-b <exe>] [-f <FD>] [-p] [--] <binary> [<args>]\n"
 	    "\n"
 	    "Options:\n"
 	    "  -h        Display this help message\n"
+	    "  -b <exe>  Execute <exe> instead of <binary>, arg0 is <binary>\n"
 	    "  -f <FD>   Execute <FD> instead of searching for <binary>\n"
 	    "  -p        Search in PATH for named binary\n"
 	    "  -v        Display identification information\n"