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@xxxxxxxxxxxx>
Tested-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
>
> Signed-off-by: Ignacio Encinas <ignacio@xxxxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxx>
>
