[v1] selftests: riscv: fix v_exec_initval_nolibc.c

[PATCH] selftests: riscv: fix v_exec_initval_nolibc.c

Posted by Ignacio Encinas 11 months, 1 week ago

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@iencinas.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@iencinas.com>

Re: [PATCH] selftests: riscv: fix v_exec_initval_nolibc.c

Posted by Charlie Jenkins 11 months, 1 week ago

On Wed, Mar 05, 2025 at 05:39:28PM +0100, Ignacio Encinas wrote:
> 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.

This check was included because the "dirty" value is an implementation
detail that I believe is not strongly defined in the ABI. Since linux
does always set this value to zero (currently) we can safely remove this
check. 

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>

> 
> Signed-off-by: Ignacio Encinas <ignacio@iencinas.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@iencinas.com>
>

Re: [PATCH] selftests: riscv: fix v_exec_initval_nolibc.c

Posted by Ignacio Encinas Rubio 11 months, 1 week ago

On 5/3/25 22:49, Charlie Jenkins wrote:
> On Wed, Mar 05, 2025 at 05:39:28PM +0100, Ignacio Encinas wrote:
>> 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.
> 
> This check was included because the "dirty" value is an implementation
> detail that I believe is not strongly defined in the ABI. Since linux
> does always set this value to zero (currently) we can safely remove this
> check. 

Thanks for the review. Just after sending the patch I noticed it should
also remove some code that becomes useless after this change: 
_prev_value_ and _first_ variables were only needed because two "clean" 
values were supported.

I'll send a v2 tomorrow. I'm guessing keeping your "Reviewed-by" and
"Tested-by" is the appropriate thing to do as the changes are very
simple. Let me know if that's not the case.

Thanks again!

Re: [PATCH] selftests: riscv: fix v_exec_initval_nolibc.c

Posted by Charlie Jenkins 11 months, 1 week ago

On Thu, Mar 06, 2025 at 07:31:22AM +0100, Ignacio Encinas Rubio wrote:
> 
> 
> On 5/3/25 22:49, Charlie Jenkins wrote:
> > On Wed, Mar 05, 2025 at 05:39:28PM +0100, Ignacio Encinas wrote:
> >> 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.
> > 
> > This check was included because the "dirty" value is an implementation
> > detail that I believe is not strongly defined in the ABI. Since linux
> > does always set this value to zero (currently) we can safely remove this
> > check. 
> 
> Thanks for the review. Just after sending the patch I noticed it should
> also remove some code that becomes useless after this change: 
> _prev_value_ and _first_ variables were only needed because two "clean" 
> values were supported.
> 
> I'll send a v2 tomorrow. I'm guessing keeping your "Reviewed-by" and
> "Tested-by" is the appropriate thing to do as the changes are very
> simple. Let me know if that's not the case.
> 
> Thanks again!

Yes, those changes seem small so you can keep the tags :)

- Charlie