S390_RUNTIME_INSTR(2)

NAME
s390_runtime_instr - enable/disable s390 CPU run-time instrumentation

SYNOPSIS
#include <asm/runtime_instr.h> /* Definition of S390_* constants */
#include <sys/syscall.h>       /* Definition of SYS_* constants */
#include <unistd.h>

int syscall(SYS_s390_runtime_instr, int command, int signum);

Note: glibc provides no wrapper for s390_runtime_instr(), necessitating the use of syscall(2).

DESCRIPTION
The s390_runtime_instr() system call starts or stops CPU run-time instrumentation for the calling thread.

The command argument controls whether run-time instrumentation is started (S390_RUNTIME_INSTR_START, 1) or stopped (S390_RUNTIME_INSTR_STOP, 2) for the calling thread.

The signum argument specifies the number of a real-time signal. This argument was used to specify a signal number that should be delivered to the thread if the run-time instrumentation buffer was full or if the run-time-instrumentation-halted interrupt had occurred. This feature was never used, and in Linux 4.4 support for this feature was removed; thus, in current kernels, this argument is ignored.

RETURN VALUE
On success, s390_runtime_instr() returns 0 and enables the thread for run-time instrumentation by assigning the thread a default run-time instrumentation control block. The caller can then read and modify the control block and start the run-time instrumentation. On error, -1 is returned and errno is set to indicate the error.

ERRORS

EINVAL
    The value specified in command is not a valid command.

EINVAL
    The value specified in signum is not a real-time signal number. From Linux 4.4 onwards, the signum argument has no effect, so that an invalid signal number will not result in an error.

ENOMEM
    Allocating memory for the run-time instrumentation control block failed.

EOPNOTSUPP
    The run-time instrumentation facility is not available.

VERSIONS
This system call is available since Linux 3.7.

CONFORMING TO
This Linux-specific system call is available only on the s390 architecture. The run-time instrumentation facility is available beginning with System z EC12.

NOTES
The asm/runtime_instr.h header file is available since Linux 4.16.

Starting with Linux 4.4, support for signalling was removed, as was the check whether signum is a valid real-time signal. For backwards compatibility with older kernels, it is recommended to pass a valid real-time signal number in signum and install a handler for that signal.

SEE ALSO
syscall(2), signal(7)

COLOPHON
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