selftests: arm64: Add utility to set SVE vector lengths

vlset is a small utility for use in conjunction with tests like the sve-test
stress test which allows another executable to be invoked with a configured
SVE vector length.
Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20200819114837.51466-5-broonie@kernel.orgSigned-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/fp/vlset.c

+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2015-2019 ARM Limited.
+ * Original author: Dave Martin <Dave.Martin@arm.com>
+ */
+#define _GNU_SOURCE
+#include <assert.h>
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <unistd.h>
+#include <sys/auxv.h>
+#include <sys/prctl.h>
+#include <asm/hwcap.h>
+#include <asm/sigcontext.h>
+
+static int inherit = 0;
+static int no_inherit = 0;
+static int force = 0;
+static unsigned long vl;
+
+static const struct option options[] = {
+	{ "force",	no_argument, NULL, 'f' },
+	{ "inherit",	no_argument, NULL, 'i' },
+	{ "max",	no_argument, NULL, 'M' },
+	{ "no-inherit",	no_argument, &no_inherit, 1 },
+	{ "help",	no_argument, NULL, '?' },
+	{}
+};
+
+static char const *program_name;
+
+static int parse_options(int argc, char **argv)
+{
+	int c;
+	char *rest;
+
+	program_name = strrchr(argv[0], '/');
+	if (program_name)
+		++program_name;
+	else
+		program_name = argv[0];
+
+	while ((c = getopt_long(argc, argv, "Mfhi", options, NULL)) != -1)
+		switch (c) {
+		case 'M':	vl = SVE_VL_MAX; break;
+		case 'f':	force = 1; break;
+		case 'i':	inherit = 1; break;
+		case 0:		break;
+		default:	goto error;
+		}
+
+	if (inherit && no_inherit)
+		goto error;
+
+	if (!vl) {
+		/* vector length */
+		if (optind >= argc)
+			goto error;
+
+		errno = 0;
+		vl = strtoul(argv[optind], &rest, 0);
+		if (*rest) {
+			vl = ULONG_MAX;
+			errno = EINVAL;
+		}
+		if (vl == ULONG_MAX && errno) {
+			fprintf(stderr, "%s: %s: %s\n",
+				program_name, argv[optind], strerror(errno));
+			goto error;
+		}
+
+		++optind;
+	}
+
+	/* command */
+	if (optind >= argc)
+		goto error;
+
+	return 0;
+
+error:
+	fprintf(stderr,
+		"Usage: %s [-f | --force] "
+		"[-i | --inherit | --no-inherit] "
+		"{-M | --max | <vector length>} "
+		"<command> [<arguments> ...]\n",
+		program_name);
+	return -1;
+}
+
+int main(int argc, char **argv)
+{
+	int ret = 126;	/* same as sh(1) command-not-executable error */
+	long flags;
+	char *path;
+	int t, e;
+
+	if (parse_options(argc, argv))
+		return 2;	/* same as sh(1) builtin incorrect-usage */
+
+	if (vl & ~(vl & PR_SVE_VL_LEN_MASK)) {
+		fprintf(stderr, "%s: Invalid vector length %lu\n",
+			program_name, vl);
+		return 2;	/* same as sh(1) builtin incorrect-usage */
+	}
+
+	if (!(getauxval(AT_HWCAP) & HWCAP_SVE)) {
+		fprintf(stderr, "%s: Scalable Vector Extension not present\n",
+			program_name);
+
+		if (!force)
+			goto error;
+
+		fputs("Going ahead anyway (--force):  "
+		      "This is a debug option.  Don't rely on it.\n",
+		      stderr);
+	}
+
+	flags = PR_SVE_SET_VL_ONEXEC;
+	if (inherit)
+		flags |= PR_SVE_VL_INHERIT;
+
+	t = prctl(PR_SVE_SET_VL, vl | flags);
+	if (t < 0) {
+		fprintf(stderr, "%s: PR_SVE_SET_VL: %s\n",
+			program_name, strerror(errno));
+		goto error;
+	}
+
+	t = prctl(PR_SVE_GET_VL);
+	if (t == -1) {
+		fprintf(stderr, "%s: PR_SVE_GET_VL: %s\n",
+			program_name, strerror(errno));
+		goto error;
+	}
+	flags = PR_SVE_VL_LEN_MASK;
+	flags = t & ~flags;
+
+	assert(optind < argc);
+	path = argv[optind];
+
+	execvp(path, &argv[optind]);
+	e = errno;
+	if (errno == ENOENT)
+		ret = 127;	/* same as sh(1) not-found error */
+	fprintf(stderr, "%s: %s: %s\n", program_name, path, strerror(e));
+
+error:
+	return ret;		/* same as sh(1) not-executable error */
+}