PR_SVE_SET_VL(2const)                                    PR_SVE_SET_VL(2const)

NAME
       PR_SVE_SET_VL - set the thread's SVE vector length

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <linux/prctl.h>  /* Definition of PR_* constants */
       #include <sys/prctl.h>

       int prctl(PR_SVE_SET_VL, unsigned long val);

DESCRIPTION
       Configure the thread's SVE vector length, as specified by val.

       The bits of val corresponding to PR_SVE_VL_LEN_MASK must be set to the
       desired vector length in bytes.  This is interpreted as an upper bound:
       the kernel will select the greatest available vector length that does
       not exceed the value specified.  In particular, specifying SVE_VL_MAX
       (defined in <asm/sigcontext.h>) for the PR_SVE_VL_LEN_MASK bits
       requests the maximum supported vector length.

       In addition, the other bits of val must be set to one of the following
       combinations of flags:

       0L     Perform the change immediately.  At the next execve(2) in the
              thread, the vector length will be reset to the value configured
              in /proc/sys/abi/sve_default_vector_length.

       PR_SVE_VL_INHERIT
              Perform the change immediately.  Subsequent execve(2) calls will
              preserve the new vector length.

       PR_SVE_SET_VL_ONEXEC
              Defer the change, so that it is performed at the next execve(2)
              in the thread.  Further execve(2) calls will reset the vector
              length to the value configured in /proc/sys/abi/
              sve_default_vector_length.

       PR_SVE_SET_VL_ONEXEC | PR_SVE_VL_INHERIT
              Defer the change, so that it is performed at the next execve(2)
              in the thread.  Further execve(2) calls will preserve the new
              vector length.

       In all cases, any previously pending deferred change is canceled.

       On success, a nonnegative value is returned that describes the selected
       configuration.  If PR_SVE_SET_VL_ONEXEC was included in val, then the
       configuration described by the return value will take effect at the
       next execve(2).  Otherwise, the configuration is already in effect when
       the PR_SVE_SET_VL call returns.  In either case, the value is encoded
       in the same way as the return value of PR_SVE_GET_VL.  Note that there
       is no explicit flag in the return value corresponding to
       PR_SVE_SET_VL_ONEXEC.

       The configuration (including any pending deferred change) is inherited
       across fork(2) and clone(2).

RETURN VALUE
       On success, PR_SVE_SET_VL returns the nonnegative value described
       above.  On error, -1 is returned, and errno is set to indicate the
       error.

ERRORS
       EINVAL SVE is not available on this platform.

       EINVAL The value in the bits of val corresponding to PR_SVE_VL_LEN_MASK
              is outside the range [SVE_VL_MIN, SVE_VL_MAX] or is not a
              multiple of 16.

       EINVAL The other bits of val are invalid or unsupported.

FILES
       /proc/sys/abi/sve_default_vector_length

STANDARDS
       Linux.  arm64 only.

HISTORY
       Linux 4.15 (arm64).

CAVEATS
       Because the compiler or run-time environment may be using SVE, using
       this call without the PR_SVE_SET_VL_ONEXEC flag may crash the calling
       process.  The conditions for using it safely are complex and system-
       dependent.  Don't use it unless you really know what you are doing.

SEE ALSO
       prctl(2), PR_SVE_GET_VL(2const)

       For more information, see the kernel source file
       Documentation/arm64/sve.rst (or Documentation/arm64/sve.txt before
       Linux 5.3).

Linux man-pages 6.9.1             2024-06-02             PR_SVE_SET_VL(2const)