kselftest/arm64: Remove assumption that tasks start FPSIMD only

Currently the sve-ptrace test for setting and reading FPSIMD data assumes
that the child will start off in FPSIMD only mode and that it can use this
to read some FPSIMD mode SVE ptrace data, skipping the test if it can't.
This isn't an assumption guaranteed by the ABI and also limits how we can
use this testcase within the program. Instead skip the initial read and
just generate a FPSIMD format buffer for the write part of the test, making
the coverage more robust in the face of future kernel and test program
changes.
Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220404090613.181272-3-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

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

@@ -46,7 +46,7 @@ static const struct vec_type vec_types[] = {
 
 #define VL_TESTS (((SVE_VQ_MAX - SVE_VQ_MIN) + 1) * 3)
 #define FLAG_TESTS 2
-#define FPSIMD_TESTS 3
+#define FPSIMD_TESTS 2
 
 #define EXPECTED_TESTS ((VL_TESTS + FLAG_TESTS + FPSIMD_TESTS) * ARRAY_SIZE(vec_types))
 
@@ -240,28 +240,24 @@ static void check_u32(unsigned int vl, const char *reg,
 /* Access the FPSIMD registers via the SVE regset */
 static void ptrace_sve_fpsimd(pid_t child, const struct vec_type *type)
 {
-	void *svebuf = NULL;
-	size_t svebufsz = 0;
+	void *svebuf;
 	struct user_sve_header *sve;
 	struct user_fpsimd_state *fpsimd, new_fpsimd;
 	unsigned int i, j;
 	unsigned char *p;
+	int ret;
 
-	/* New process should start with FPSIMD registers only */
-	sve = get_sve(child, type, &svebuf, &svebufsz);
-	if (!sve) {
-		ksft_test_result_fail("get_sve(%s): %s\n",
-				      type->name, strerror(errno));
-
+	svebuf = malloc(SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD));
+	if (!svebuf) {
+		ksft_test_result_fail("Failed to allocate FPSIMD buffer\n");
 		return;
-	} else {
-		ksft_test_result_pass("get_sve(%s FPSIMD)\n", type->name);
 	}
 
-	ksft_test_result((sve->flags & SVE_PT_REGS_MASK) == SVE_PT_REGS_FPSIMD,
-			 "Got FPSIMD registers via %s\n", type->name);
-	if ((sve->flags & SVE_PT_REGS_MASK) != SVE_PT_REGS_FPSIMD)
-		goto out;
+	memset(svebuf, 0, SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD));
+	sve = svebuf;
+	sve->flags = SVE_PT_REGS_FPSIMD;
+	sve->size = SVE_PT_SIZE(0, SVE_PT_REGS_FPSIMD);
+	sve->vl = 16;  /* We don't care what the VL is */
 
 	/* Try to set a known FPSIMD state via PT_REGS_SVE */
 	fpsimd = (struct user_fpsimd_state *)((char *)sve +
@@ -273,12 +269,11 @@ static void ptrace_sve_fpsimd(pid_t child, const struct vec_type *type)
 			p[j] = j;
 	}
 
-	if (set_sve(child, type, sve)) {
-		ksft_test_result_fail("set_sve(%s FPSIMD): %s\n",
-				      type->name, strerror(errno));
-
+	ret = set_sve(child, type, sve);
+	ksft_test_result(ret == 0, "%s FPSIMD set via SVE: %d\n",
+			 type->name, ret);
+	if (ret)
 		goto out;
-	}
 
 	/* Verify via the FPSIMD regset */
 	if (get_fpsimd(child, &new_fpsimd)) {
@@ -548,11 +543,9 @@ static int do_parent(pid_t child)
 		if (getauxval(vec_types[i].hwcap_type) & vec_types[i].hwcap) {
 			ptrace_sve_fpsimd(child, &vec_types[i]);
 		} else {
-			ksft_test_result_skip("%s FPSIMD get via SVE\n",
-					      vec_types[i].name);
 			ksft_test_result_skip("%s FPSIMD set via SVE\n",
 					      vec_types[i].name);
-			ksft_test_result_skip("%s set read via FPSIMD\n",
+			ksft_test_result_skip("%s FPSIMD read\n",
 					      vec_types[i].name);
 		}