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