kselftest/arm64: Add test case for POR_EL0 signal frame records

Ensure that we get signal context for POR_EL0 if and only if POE is present
on the system.

Copied from the TPIDR2 test.

Signed-off-by: Joey Gouly <joey.gouly@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20240822151113.1479789-30-joey.gouly@arm.com
Signed-off-by: Will Deacon <will@kernel.org>

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

@@ -2,6 +2,7 @@
 mangle_*
 fake_sigreturn_*
 fpmr_*
+poe_*
 sme_*
 ssve_*
 sve_*

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

@@ -0,0 +1,86 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2023 Arm Limited
+ *
+ * Verify that the POR_EL0 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_POR_EL0 "S3_3_C10_C2_4"
+
+static uint64_t get_por_el0(void)
+{
+	uint64_t val;
+
+	asm volatile(
+		"mrs	%0, " SYS_POR_EL0 "\n"
+		: "=r"(val)
+		:
+		: );
+
+	return val;
+}
+
+int poe_present(struct tdescr *td, siginfo_t *si, ucontext_t *uc)
+{
+	struct _aarch64_ctx *head = GET_BUF_RESV_HEAD(context);
+	struct poe_context *poe_ctx;
+	size_t offset;
+	bool in_sigframe;
+	bool have_poe;
+	__u64 orig_poe;
+
+	have_poe = getauxval(AT_HWCAP2) & HWCAP2_POE;
+	if (have_poe)
+		orig_poe = get_por_el0();
+
+	if (!get_current_context(td, &context.uc, sizeof(context)))
+		return 1;
+
+	poe_ctx = (struct poe_context *)
+		get_header(head, POE_MAGIC, td->live_sz, &offset);
+
+	in_sigframe = poe_ctx != NULL;
+
+	fprintf(stderr, "POR_EL0 sigframe %s on system %s POE\n",
+		in_sigframe ? "present" : "absent",
+		have_poe ? "with" : "without");
+
+	td->pass = (in_sigframe == have_poe);
+
+	/*
+	 * Check that the value we read back was the one present at
+	 * the time that the signal was triggered.
+	 */
+	if (have_poe && poe_ctx) {
+		if (poe_ctx->por_el0 != orig_poe) {
+			fprintf(stderr, "POR_EL0 in frame is %llx, was %llx\n",
+				poe_ctx->por_el0, orig_poe);
+			td->pass = false;
+		}
+	}
+
+	return 0;
+}
+
+struct tdescr tde = {
+	.name = "POR_EL0",
+	.descr = "Validate that POR_EL0 is present as expected",
+	.timeout = 3,
+	.run = poe_present,
+};