kldxref: Add -m filag to print info about modules in one file

kldxref -m <file> will print the same data that the '-d' flag produces,
except restrict the output to one file. This should be the full path to
the file, and the directory name to process is omitted.

Sponsored by:		Netflix
Differential Revision:	https://reviews.freebsd.org/D57902

usr.sbin/kldxref/kldxref.8

@@ -24,7 +24,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd February 25, 2023
+.Dd June 27, 2026
 .Dt KLDXREF 8
 .Os
 .Sh NAME
@@ -35,6 +35,8 @@
 .Op Fl Rdv
 .Op Fl f Ar hintsfile
 .Ar path ...
+.Nm
+.Fl m Ar module
 .Sh DESCRIPTION
 The
 .Nm
@@ -67,6 +69,9 @@ output.
 .It Fl f Ar hintsfile
 Specify a different name for the hints files than
 .Pa linker.hints .
+.It Fl m Ar module
+Print information about the modules in the file
+.Ar module .
 .It Fl v
 Operate in verbose mode.
 .El

usr.sbin/kldxref/kldxref.c

@@ -764,13 +764,13 @@ main(int argc, char *argv[])
 {
 	FTS *ftsp;
 	FTSENT *p;
-	char *dot = NULL;
+	char *dot = NULL, *module = NULL;
 	int opt, fts_options;
 	struct stat sb;
 
 	fts_options = FTS_PHYSICAL;
 
-	while ((opt = getopt(argc, argv, "Rdf:v")) != -1) {
+	while ((opt = getopt(argc, argv, "Rdf:m:v")) != -1) {
 		switch (opt) {
 		case 'd':	/* no hint file, only print on stdout */
 			dflag = true;
@@ -778,6 +778,10 @@ main(int argc, char *argv[])
 		case 'f':	/* use this name instead of linker.hints */
 			xref_file = optarg;
 			break;
+		case 'm':
+			module = optarg;
+			dflag = true;
+			break;
 		case 'v':
 			verbose++;
 			break;
@@ -789,11 +793,18 @@ main(int argc, char *argv[])
 			/* NOTREACHED */
 		}
 	}
-	if (argc - optind < 1)
+	if (argc - optind < (module ? 0 : 1))
 		usage();
 	argc -= optind;
 	argv += optind;
 
+	if (module) {
+		if (elf_version(EV_CURRENT) == EV_NONE)
+			errx(1, "unsupported libelf");
+		read_kld(module, module);
+		exit(0);
+	}
+
 	if (stat(argv[0], &sb) != 0)
 		err(1, "%s", argv[0]);
 	if ((sb.st_mode & S_IFDIR) == 0 && !dflag) {