Provided by: systemtap-doc_2.9-2ubuntu2_all 

NAME
function::registers_valid - Determines validity of register and u_register in current context
SYNOPSIS
registers_valid:long()
ARGUMENTS
None
DESCRIPTION
This function returns 1 if register and u_register can be used in the current context, or 0 otherwise.
For example, registers_valid returns 0 when called from a begin or end probe.
SEE ALSO
tapset::context(3stap)
SystemTap Tapset Reference April 2016 FUNCTION::REGISTERS_(3stap)