selftests: Test RISC-V Vector's first-use handler

This add a test to check if the kernel zero-initializes all V registers
after the first-use trap handler returns.

If V registers are not zero-initialized, then the test should fail one
out of several runs:

```
 root@sifive-fpga:~# ./v_initval_nolibc
 # vl = 256
 not ok 1 detect stale values on v-regesters
 0 0 0 0 0 0 0 0   0 0 0 0 0 0 0 0
 0 4c 41 4e 47 3d 43 0   50 41 54 48 3d 2f 75 73
 72 2f 6c 6f 63 61 6c 2f   73 62 69 6e 3a 2f 75 73
 72 2f 6c 6f 63 61 6c 2f   62 69 6e 3a 2f 75 73 72
 ff ff 81 0 0 0 0 0   0 0 0 0 0 0 0 0
```

Otherwise, the test passes without errors each run.

Signed-off-by: Andy Chiu <[email protected]>
Reviewed-by: Björn Töpel <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: AndybnACT

tools/testing/selftests/riscv/vector/.gitignore

@@ -1,2 +1,3 @@
 vstate_exec_nolibc
 vstate_prctl
+v_initval_nolibc

tools/testing/selftests/riscv/vector/Makefile

@@ -2,7 +2,7 @@
 # Copyright (C) 2021 ARM Limited
 # Originally tools/testing/arm64/abi/Makefile
 
-TEST_GEN_PROGS := vstate_prctl
+TEST_GEN_PROGS := vstate_prctl v_initval_nolibc
 TEST_GEN_PROGS_EXTENDED := vstate_exec_nolibc
 
 include ../../lib.mk
@@ -13,3 +13,7 @@ $(OUTPUT)/vstate_prctl: vstate_prctl.c ../hwprobe/sys_hwprobe.S
 $(OUTPUT)/vstate_exec_nolibc: vstate_exec_nolibc.c
 	$(CC) -nostdlib -static -include ../../../../include/nolibc/nolibc.h \
 		-Wall $(CFLAGS) $(LDFLAGS) $^ -o $@ -lgcc
+
+$(OUTPUT)/v_initval_nolibc: v_initval_nolibc.c
+	$(CC) -nostdlib -static -include ../../../../include/nolibc/nolibc.h \
+		-Wall $(CFLAGS) $(LDFLAGS) $^ -o $@ -lgcc

tools/testing/selftests/riscv/vector/v_initval_nolibc.c

@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#include "../../kselftest.h"
+#define MAX_VSIZE	(8192 * 32)
+
+void dump(char *ptr, int size)
+{
+	int i = 0;
+
+	for (i = 0; i < size; i++) {
+		if (i != 0) {
+			if (i % 16 == 0)
+				printf("\n");
+			else if (i % 8 == 0)
+				printf("  ");
+		}
+		printf("%02x ", ptr[i]);
+	}
+	printf("\n");
+}
+
+int main(void)
+{
+	int i;
+	unsigned long vl;
+	char *datap, *tmp;
+
+	datap = malloc(MAX_VSIZE);
+	if (!datap) {
+		ksft_test_result_fail("fail to allocate memory for size = %lu\n", MAX_VSIZE);
+		exit(-1);
+	}
+
+	tmp = datap;
+	asm volatile (
+		".option push\n\t"
+		".option arch, +v\n\t"
+		"vsetvli	%0, x0, e8, m8, ta, ma\n\t"
+		"vse8.v		v0, (%2)\n\t"
+		"add		%1, %2, %0\n\t"
+		"vse8.v		v8, (%1)\n\t"
+		"add		%1, %1, %0\n\t"
+		"vse8.v		v16, (%1)\n\t"
+		"add		%1, %1, %0\n\t"
+		"vse8.v		v24, (%1)\n\t"
+		".option pop\n\t"
+		: "=&r" (vl), "=r" (tmp) : "r" (datap) : "memory");
+
+	ksft_print_msg("vl = %lu\n", vl);
+
+	if (datap[0] != 0x00 && datap[0] != 0xff) {
+		ksft_test_result_fail("v-regesters are not properly initialized\n");
+		dump(datap, vl * 4);
+		exit(-1);
+	}
+
+	for (i = 1; i < vl * 4; i++) {
+		if (datap[i] != datap[0]) {
+			ksft_test_result_fail("detect stale values on v-regesters\n");
+			dump(datap, vl * 4);
+			exit(-2);
+		}
+	}
+
+	free(datap);
+	ksft_exit_pass();
+	return 0;
+}