setarch: make <arch> optional

Let's allow to change personality flags without execution domain
modification.

Old way:
  setarch `arch` --addr-no-randomize myprog

New way:
  setarch --addr-no-randomize myprog

Addresses: https://github.com/karelzak/util-linux/issues/668
Signed-off-by: Karel Zak <kzak@redhat.com>

2 files changed, 39 insertions, 15 deletions

diff --git a/sys-utils/setarch.8 b/sys-utils/setarch.8
index 2a701fa57..d0fd5b945 100644
--- a/sys-utils/setarch.8
+++ b/sys-utils/setarch.8
@@ -1,27 +1,36 @@
 .TH SETARCH 8 "December 2017" "util-linux" "System Administration"
 .SH NAME
-setarch \- change reported architecture in new program environment and set personality flags
+setarch \- change reported architecture in new program environment and/or set personality flags
 .SH SYNOPSIS
 .B setarch
-.I arch
+.RI [ arch ]
 [options]
 .RI [ program
 .RI [ argument ...]]
 .sp
+.B setarch
+.BR \-\-list | \-h | \-V
+.sp
 .B arch
 [options]
 .RI [ program
 .RI [ argument ...]]
-.sp
-.B setarch
-.BR \-\-list | \-h | \-V
 .SH DESCRIPTION
 .B setarch
-currently only affects the output of \fBuname -m\fR.
+modifies execution domains and process personality flags.
+.PP
+The execution domains currently only affects the output of \fBuname -m\fR.
 For example, on an AMD64 system, running \fBsetarch i386 \fIprogram\fR
 will cause \fIprogram\fR to see i686 instead of x86_64 as the machine type.
 It also allows to set various personality options.
 The default \fIprogram\fR is \fB/bin/sh\fR.
+.PP
+Since version 2.33 the
+.I arch
+comnand line argument is optional and
+.B setarch
+may be used to change personality flags (ADDR_LIMIT_*, SHORT_INODE, etc) without
+modification of the execution domain.
 .SH OPTIONS
 .TP
 .B \-\-list
@@ -105,6 +114,8 @@ Display version information and exit.
 .BR \-h , " \-\-help"
 Display help text and exit.
 .SH EXAMPLES
+setarch --addr-no-randomize mytestprog
+.br
 setarch ppc32 rpmbuild --target=ppc --rebuild foo.src.rpm
 .br
 setarch ppc32 -v -vL3 rpmbuild --target=ppc --rebuild bar.src.rpm
@@ -118,6 +129,10 @@ Elliot Lee
 .MT jnovy@redhat.com
 Jindrich Novy
 .ME
+.br
+.MT kzak@redhat.com
+Karel Zak
+.ME
 .SH "SEE ALSO"
 .BR personality (2),
 .BR select (2)
diff --git a/sys-utils/setarch.c b/sys-utils/setarch.c
index fc5764f82..a733f7b3c 100644
--- a/sys-utils/setarch.c
+++ b/sys-utils/setarch.c
@@ -94,7 +94,7 @@ static void __attribute__((__noreturn__)) usage(int archwrapper)
 {
 	fputs(USAGE_HEADER, stdout);
 	if (!archwrapper)
-		printf(_(" %s <arch> [options] [<program> [<argument>...]]\n"), program_invocation_short_name);
+		printf(_(" %s [<arch>] [options] [<program> [<argument>...]]\n"), program_invocation_short_name);
 	else
 		printf(_(" %s [options] [<program> [<argument>...]]\n"), program_invocation_short_name);
 
@@ -385,19 +385,26 @@ int main(int argc, char *argv[])
 		}
 	}
 
-	if (!arch)
-		errx(EXIT_FAILURE, _("no architecture argument specified"));
+	if (!arch && !options)
+		errx(EXIT_FAILURE, _("no architecture argument or personality flags specified"));
 
 	argc -= optind;
 	argv += optind;
 
-	doms = init_arch_domains();
+	/* get execution domain (architecture) */
+	if (arch) {
+		doms = init_arch_domains();
+		target = get_arch_domain(doms, arch);
 
-	target = get_arch_domain(doms, arch);
-	if (!target)
-		errx(EXIT_FAILURE, _("%s: Unrecognized architecture"), arch);
+		if (!target)
+			errx(EXIT_FAILURE, _("%s: Unrecognized architecture"), arch);
+		pers_value = target->perval;
+	}
+
+	/* add personality flags */
+	pers_value |= options;
 
-	pers_value = target->perval | options;
+	/* call kernel */
 	if (personality(pers_value) < 0) {
 		/*
 		 * Depending on architecture and kernel version, personality
@@ -411,7 +418,9 @@ int main(int argc, char *argv[])
 			err(EXIT_FAILURE, _("failed to set personality to %s"), arch);
 	}
 
-	verify_arch_domain(target, arch);
+	/* make sure architecture is set as expected */
+	if (arch)
+		verify_arch_domain(target, arch);
 
 	if (verbose) {
 		printf(_("Execute command `%s'.\n"), argc ? argv[0] : "/bin/sh");