Introduce --argv0 option

This option is useful for tracing multi-call executables which interpret
argv[0], such as busybox or kmod.

* NEWS: Mention this.
* doc/strace.1.in: Document this.
* src/strace.c (usage): Likewise.
(argv0): New variable.
(startup_child): Use it.
(GETOPT_ARGV0): New enum constant.
(longopts, init): Use it.

Co-authored-by: Dmitry V. Levin <ldv@strace.io>
Resolves: https://github.com/strace/strace/pull/248

3 files changed, 20 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index bcb3c1a94..e1d3f12c8 100644
--- a/NEWS
+++ b/NEWS
@@ -8,6 +8,7 @@ Noteworthy changes in release ?.? (????-??-??)
     that operate on the specified set of file descriptors.
   * Implemented --syscall-limit option to automatically detach tracees
     after capturing the specified number of syscalls.
+  * Implemented --argv0 option to set argv[0] of the command being executed.
   * Implemented decoding of PR_GET_MDWE and PR_SET_MDWE operations of prctl
     syscall.
   * Implemented decoding of IP_LOCAL_PORT_RANGE socket option.
diff --git a/doc/strace.1.in b/doc/strace.1.in
index 986e97eee..4d5730ed6 100644
--- a/doc/strace.1.in
+++ b/doc/strace.1.in
@@ -353,6 +353,12 @@ This option is only useful when running as root and enables the
 correct execution of setuid and/or setgid binaries.
 Unless this option is used setuid and setgid programs are executed
 without effective privileges.
+.TP
+.BR "\-\-argv0" = \fIname\fR
+Set argv[0] of the command being executed to
+.IR name .
+Useful for tracing multi-call executables which interpret argv[0],
+such as busybox or kmod.
 .SS Tracing
 .TP 12
 .BI "\-b " syscall
diff --git a/src/strace.c b/src/strace.c
index 265c0c6dc..85d69485f 100644
--- a/src/strace.c
+++ b/src/strace.c
@@ -186,6 +186,8 @@ static size_t tcb_wait_tab_size;
 char *program_invocation_name;
 #endif
 
+char *argv0; /* override argv[0] on execve */
+
 unsigned os_release; /* generated from uname()'s u.release */
 
 static void detach(struct tcb *tcp);
@@ -303,6 +305,7 @@ Startup:\n\
                  trace process with process id PID, may be repeated\n\
   -u USERNAME, --user=USERNAME\n\
                  run command as USERNAME handling setuid and/or setgid\n\
+  --argv0=NAME   set PROG argv[0] to NAME\n\
 \n\
 Tracing:\n\
   -b execve, --detach-on=execve\n\
@@ -1675,6 +1678,8 @@ startup_child(char **argv, char **env)
 	params_for_tracee.run_euid = (statbuf.st_mode & S_ISUID) ? statbuf.st_uid : run_uid;
 	params_for_tracee.run_egid = (statbuf.st_mode & S_ISGID) ? statbuf.st_gid : run_gid;
 	params_for_tracee.argv = argv;
+	if (argv0)
+		params_for_tracee.argv[0] = argv0;
 	params_for_tracee.env = env;
 	/*
 	 * On NOMMU, can be safely freed only after execve in tracee.
@@ -2266,6 +2271,7 @@ init(int argc, char *argv[])
 		GETOPT_SYSCALL_LIMIT,
 		GETOPT_TS,
 		GETOPT_TIPS,
+		GETOPT_ARGV0,
 
 		GETOPT_QUAL_TRACE,
 		GETOPT_QUAL_TRACE_FD,
@@ -2327,6 +2333,7 @@ init(int argc, char *argv[])
 		{ "failing-only",	no_argument,	   0, 'Z' },
 		{ "seccomp-bpf",	no_argument,	   0, GETOPT_SECCOMP },
 		{ "tips",		optional_argument, 0, GETOPT_TIPS },
+		{ "argv0",		required_argument, 0, GETOPT_ARGV0 },
 
 		{ "trace",	required_argument, 0, GETOPT_QUAL_TRACE },
 		{ "trace-fds",	required_argument, 0, GETOPT_QUAL_TRACE_FD },
@@ -2564,6 +2571,9 @@ init(int argc, char *argv[])
 			if (parse_tips_arg(optarg ?: ""))
 				error_opt_arg(c, lopt, optarg);
 			break;
+		case GETOPT_ARGV0:
+			argv0 = optarg;
+			break;
 		case GETOPT_QUAL_SECONTEXT:
 			qualify_secontext(optarg ? optarg : secontext_qual);
 			break;
@@ -2634,6 +2644,9 @@ init(int argc, char *argv[])
 		error_msg_and_help("must have PROG [ARGS] or -p PID");
 	}
 
+	if (!argc && argv0)
+		error_msg_and_help("PROG [ARGS] must be specified with --argv0");
+
 	if (daemonized_tracer_long) {
 		if (daemonized_tracer) {
 			error_msg_and_die("-D and --daemonize cannot"