elftcl: add -i flag to ignore unknown flags

This may allow an identical elfctl invocation to be used on multiple
FreeBSD versions, with features not implemented on older releases being
silently ignored.

PR:		252629 (related)
Reviewed by:	kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D28130

usr.bin/elfctl/elfctl.1

@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd March 1, 2020
+.Dd January 12, 2021
 .Dt ELFCTL 1
 .Os
 .Sh NAME
@@ -35,6 +35,7 @@
 .Sh SYNOPSIS
 .Nm
 .Op Fl h | Fl -help
+.Op Fl i
 .Op Fl l
 .Op Fl e Ar featurelist
 .Ar
@@ -47,6 +48,9 @@ The options are as follows:
 .Bl -tag -width indent
 .It Fl h | Fl -help
 Print a usage message and exit.
+.It Fl i
+Ignore unknown feature flags in
+.Ar featurelist .
 .It Fl l
 List known ELF feature flags.
 .It Fl e Ar featurelist

usr.bin/elfctl/elfctl.c

@@ -81,7 +81,9 @@ static struct option long_opts[] = {
 #else
 #define SUPPORTED_ENDIAN ELFDATA2MSB
 #endif
-		
+
+static bool iflag;
+
 int
 main(int argc, char **argv)
 {
@@ -100,8 +102,11 @@ main(int argc, char **argv)
 	if (elf_version(EV_CURRENT) == EV_NONE)
 		errx(EXIT_FAILURE, "elf_version error");
 
-	while ((ch = getopt_long(argc, argv, "hle:", long_opts, NULL)) != -1) {
+	while ((ch = getopt_long(argc, argv, "hile:", long_opts, NULL)) != -1) {
 		switch (ch) {
+		case 'i':
+			iflag = true;
+			break;
 		case 'l':
 			print_features();
 			lflag = true;
@@ -197,6 +202,7 @@ Usage: %s [options] file...\n\
   Set or display the control features for an ELF object.\n\n\
   Supported options are:\n\
   -l                        List known control features.\n\
+  -i                        Ignore unknown features.\n\
   -e [+-=]feature,list      Edit features from a comma separated list.\n\
   -h | --help               Print a usage message and exit.\n"
 
@@ -229,7 +235,8 @@ convert_to_feature_val(char *feature_str, uint32_t *feature_val)
 		}
 		if (i == len) {
 			warnx("%s is not a valid feature", feature);
-			return (false);
+			if (!iflag)
+				return (false);
 		}
 	}