kselftest/arm64: Add basic FPMR test

Verify that a FPMR frame is generated on systems that support FPMR and not
generated otherwise.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20240306-arm64-2023-dpisa-v5-8-c568edc8ed7f@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/signal/.gitignore

@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
 mangle_*
 fake_sigreturn_*
+fpmr_*
 sme_*
 ssve_*
 sve_*

tools/testing/selftests/arm64/signal/testcases/fpmr_siginfo.c

@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 ARM Limited
+ *
+ * Verify that the FPMR register context in signal frames is set up as
+ * expected.
+ */
+
+#include <signal.h>
+#include <ucontext.h>
+#include <sys/auxv.h>
+#include <sys/prctl.h>
+#include <unistd.h>
+#include <asm/sigcontext.h>
+
+#include "test_signals_utils.h"
+#include "testcases.h"
+
+static union {
+	ucontext_t uc;
+	char buf[1024 * 128];
+} context;
+
+#define SYS_FPMR "S3_3_C4_C4_2"
+
+static uint64_t get_fpmr(void)
+{
+	uint64_t val;
+
+	asm volatile (
+		"mrs	%0, " SYS_FPMR "\n"
+		: "=r"(val)
+		:
+		: "cc");
+
+	return val;
+}
+
+int fpmr_present(struct tdescr *td, siginfo_t *si, ucontext_t *uc)
+{
+	struct _aarch64_ctx *head = GET_BUF_RESV_HEAD(context);
+	struct fpmr_context *fpmr_ctx;
+	size_t offset;
+	bool in_sigframe;
+	bool have_fpmr;
+	__u64 orig_fpmr;
+
+	have_fpmr = getauxval(AT_HWCAP2) & HWCAP2_FPMR;
+	if (have_fpmr)
+		orig_fpmr = get_fpmr();
+
+	if (!get_current_context(td, &context.uc, sizeof(context)))
+		return 1;
+
+	fpmr_ctx = (struct fpmr_context *)
+		get_header(head, FPMR_MAGIC, td->live_sz, &offset);
+
+	in_sigframe = fpmr_ctx != NULL;
+
+	fprintf(stderr, "FPMR sigframe %s on system %s FPMR\n",
+		in_sigframe ? "present" : "absent",
+		have_fpmr ? "with" : "without");
+
+	td->pass = (in_sigframe == have_fpmr);
+
+	if (have_fpmr && fpmr_ctx) {
+		if (fpmr_ctx->fpmr != orig_fpmr) {
+			fprintf(stderr, "FPMR in frame is %llx, was %llx\n",
+				fpmr_ctx->fpmr, orig_fpmr);
+			td->pass = false;
+		}
+	}
+
+	return 0;
+}
+
+struct tdescr tde = {
+	.name = "FPMR",
+	.descr = "Validate that FPMR is present as expected",
+	.timeout = 3,
+	.run = fpmr_present,
+};