Re: [PATCH 4/5] scripts: Added Vector Length Set test helper script

[Szabolcs Nagy via Libc-alpha <libc-alpha@sourceware.org>]

The 03/17/2021 02:35, Naohiro Tamura wrote:
> +"""Set Scalable Vector Length test helper.
> +
> +Set Scalable Vector Length for child process.
> +
> +examples:
> +
> +ubuntu@bionic:~/build$ make check subdirs=string \
> +test-wrapper='~/glibc/scripts/vltest.py 16'
> +
> +ubuntu@bionic:~/build$ ~/glibc/scripts/vltest.py 16 make test \
> +t=string/test-memcpy
> +
> +ubuntu@bionic:~/build$ ~/glibc/scripts/vltest.py 32 ./debugglibc.sh \
> +string/test-memmove
> +
> +ubuntu@bionic:~/build$ ~/glibc/scripts/vltest.py 64 ./testrun.sh \
> +string/test-memset
> +"""
> +import argparse
> +from ctypes import cdll, CDLL
> +import os
> +import sys
> +
> +EXIT_SUCCESS = 0
> +EXIT_FAILURE = 1
> +EXIT_UNSUPPORTED = 77
> +
> +AT_HWCAP = 16
> +HWCAP_SVE = (1 << 22)
> +
> +PR_SVE_GET_VL = 51
> +PR_SVE_SET_VL = 50
> +PR_SVE_SET_VL_ONEXEC = (1 << 18)
> +PR_SVE_VL_INHERIT = (1 << 17)
> +PR_SVE_VL_LEN_MASK = 0xffff
> +
> +def main(args):
> +    libc = CDLL("libc.so.6")
> +    if not libc.getauxval(AT_HWCAP) & HWCAP_SVE:
> +        print("CPU doesn't support SVE")
> +        sys.exit(EXIT_UNSUPPORTED)
> +
> +    libc.prctl(PR_SVE_SET_VL,
> +               args.vl[0] | PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT)
> +    os.execvp(args.args[0], args.args)
> +    print("exec system call failure")
> +    sys.exit(EXIT_FAILURE)


this only works on a (new enough) glibc based system and python's
CDLL path lookup can fail too (it does not follow the host system
configuration).

but i think there is no simple solution without compiling c code and
this seems useful, so i'm happy to have this script.