selftests: arm64: Verify interoperation of SVE and FPSIMD register sets

After setting the FPSIMD registers via the SVE register set read them back
via the FPSIMD register set, validating that the two register sets are
interoperating and that the values we thought we set made it into the
child process.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20210913125505.52619-7-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

tools/testing/selftests/arm64/fp/sve-ptrace.c

@@ -46,6 +46,15 @@ static int do_child(void)
 	return EXIT_SUCCESS;
 }
 
+static int get_fpsimd(pid_t pid, struct user_fpsimd_state *fpsimd)
+{
+	struct iovec iov;
+
+	iov.iov_base = fpsimd;
+	iov.iov_len = sizeof(*fpsimd);
+	return ptrace(PTRACE_GETREGSET, pid, NT_PRFPREG, &iov);
+}
+
 static struct user_sve_header *get_sve(pid_t pid, void **buf, size_t *size)
 {
 	struct user_sve_header *sve;
@@ -122,7 +131,7 @@ static int do_parent(pid_t child)
 	void *svebuf = NULL, *newsvebuf;
 	size_t svebufsz = 0, newsvebufsz;
 	struct user_sve_header *sve, *new_sve;
-	struct user_fpsimd_state *fpsimd;
+	struct user_fpsimd_state *fpsimd, new_fpsimd;
 	unsigned int i, j;
 	unsigned char *p;
 	unsigned int vq;
@@ -221,7 +230,22 @@ static int do_parent(pid_t child)
 		goto error;
 	}
 
-	/* Zero the first SVE Z register */
+	/* Verify via the FPSIMD regset */
+	if (get_fpsimd(pid, &new_fpsimd)) {
+		int e = errno;
+
+		ksft_test_result_fail("get_fpsimd(): %s\n",
+				      strerror(errno));
+		if (e == ESRCH)
+			goto disappeared;
+
+		goto error;
+	}
+	if (memcmp(fpsimd, &new_fpsimd, sizeof(*fpsimd)) == 0)
+		ksft_test_result_pass("get_fpsimd() gave same state\n");
+	else
+		ksft_test_result_fail("get_fpsimd() gave different state\n");
+
 	vq = sve_vq_from_vl(sve->vl);
 
 	newsvebufsz = SVE_PT_SVE_ZREG_OFFSET(vq, 1);