linux-kernel - [PATCH v2] selftests: riscv: fix v_exec_initval

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Message-Id: <20250306-fix-v_exec_initval_nolibc-v2-1-97f9dc8a7faf@iencinas.com>
Date: Thu, 06 Mar 2025 20:49:27 +0100
From: Ignacio Encinas <ignacio@...cinas.com>
To: linux-kernel-mentees@...ts.linux.dev, skhan@...uxfoundation.org, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Alexandre Ghiti <alex@...ti.fr>, 
 Charlie Jenkins <charlie@...osinc.com>
Cc: linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org, 
 linux-kernel@...r.kernel.org, Ignacio Encinas <ignacio@...cinas.com>
Subject: [PATCH v2] selftests: riscv: fix v_exec_initval_nolibc.c

Vector registers are zero initialized by the kernel. Stop accepting
"all ones" as a clean value.

Note that this was not working as expected given that
	value == 0xff
can be assumed to be always false by the compiler as value's range is
[-128, 127]. Both GCC (-Wtype-limits) and clang
(-Wtautological-constant-out-of-range-compare) warn about this.

Reviewed-by: Charlie Jenkins <charlie@...osinc.com>
Tested-by: Charlie Jenkins <charlie@...osinc.com>
Signed-off-by: Ignacio Encinas <ignacio@...cinas.com>
---
Changes in v2:

Remove code that becomes useless now that the only "clean" value for
vector registers is 0.

- Link to v1: https://lore.kernel.org/r/20250305-fix-v_exec_initval_nolibc-v1-1-b87b60e43002@iencinas.com
---
 tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c b/tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c
index 35c0812e32de0c82a54f84bd52c4272507121e35..4dde05e45a04122b566cedc36d20b072413b00e2 100644
--- a/tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c
+++ b/tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c
@@ -6,7 +6,7 @@
  * the values. To further ensure consistency, this file is compiled without
  * libc and without auto-vectorization.
  *
- * To be "clean" all values must be either all ones or all zeroes.
+ * To be "clean" all values must be all zeroes.
  */
 
 #define __stringify_1(x...)	#x
@@ -14,9 +14,8 @@
 
 int main(int argc, char **argv)
 {
-	char prev_value = 0, value;
+	char value = 0;
 	unsigned long vl;
-	int first = 1;
 
 	if (argc > 2 && strcmp(argv[2], "x"))
 		asm volatile (
@@ -44,14 +43,11 @@ int main(int argc, char **argv)
 			"vsrl.vi " __stringify(register) ", " __stringify(register) ", 8\n\t" \
 			".option pop\n\t"					\
 			: "=r" (value));					\
-		if (first) {							\
-			first = 0;						\
-		} else if (value != prev_value || !(value == 0x00 || value == 0xff)) { \
+		if (value != 0x00) {						\
 			printf("Register " __stringify(register)		\
 				" values not clean! value: %u\n", value);	\
 			exit(-1);						\
 		}								\
-		prev_value = value;						\
 	}									\
 })
 

---
base-commit: 03d38806a902b36bf364cae8de6f1183c0a35a67
change-id: 20250301-fix-v_exec_initval_nolibc-498d976c372d

Best regards,
-- 
Ignacio Encinas <ignacio@...cinas.com>