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

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Message-Id: <20250305-fix-v_exec_initval_nolibc-v1-1-b87b60e43002@iencinas.com>
Date: Wed, 05 Mar 2025 17:39:28 +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] 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.

Signed-off-by: Ignacio Encinas <ignacio@...cinas.com>
---
I tried looking why "all ones" was previously deemed a "clean" value but
couldn't find any information. It looks like the kernel always 
zero-initializes the vector registers.

If "all ones" is still acceptable for any reason, my intention is to 
spin a v2 changing the types of `value` and `prev_value` to unsigned 
char.
---
 tools/testing/selftests/riscv/vector/v_exec_initval_nolibc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 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..b712c4d258a6cb045aa96de4a75299714866f5e6 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
@@ -46,7 +46,7 @@ int main(int argc, char **argv)
 			: "=r" (value));					\
 		if (first) {							\
 			first = 0;						\
-		} else if (value != prev_value || !(value == 0x00 || value == 0xff)) { \
+		} else if (value != prev_value || value != 0x00) {              \
 			printf("Register " __stringify(register)		\
 				" values not clean! value: %u\n", value);	\
 			exit(-1);						\

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

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