s390_guarded_storage - operations with z/Architecture guarded storage facility

#include <asm/guarded_storage.h> /* Definition of GS_* constants */
#include <sys/syscall.h> /* Definition of SYS_* constants */
#include <unistd.h>
int syscall(SYS_s390_guarded_storage, int command,
 struct gs_cb *gs_cb);

Note: glibc provides no wrapper for s390_guarded_storage(), necessitating the use of syscall(2).

The s390_guarded_storage() system call enables the use of the Guarded Storage Facility (a z/Architecture-specific feature) for user-space processes.

The guarded storage facility is a hardware feature that allows marking up to 64 memory regions (as of z14) as guarded; reading a pointer with a newly introduced "Load Guarded" (LGG) or "Load Logical and Shift Guarded" (LLGFSG) instructions will cause a range check on the loaded value and invoke a (previously set up) user-space handler if one of the guarded regions is affected.

The command argument indicates which function to perform. The following commands are supported:

GS_ENABLE

Enable the guarded storage facility for the calling task. The initial content of the guarded storage control block will be all zeros. After enablement, user-space code can use the "Load Guarded Storage Controls" (LGSC) instruction (or the load_gs_cb() function wrapper provided in the asm/guarded_storage.h header) to load an arbitrary control block. While a task is enabled, the kernel will save and restore the calling content of the guarded storage registers on context switch.

GS_DISABLE

Disables the use of the guarded storage facility for the calling task. The kernel will cease to save and restore the content of the guarded storage registers, the task-specific content of these registers is lost.

GS_SET_BC_CB

Set a broadcast guarded storage control block to the one provided in the gs_cb argument. This is called per thread and associates a specific guarded storage control block with the calling task. This control block will be used in the broadcast command GS_BROADCAST.

GS_CLEAR_BC_CB

Clears the broadcast guarded storage control block. The guarded storage control block will no longer have the association established by the GS_SET_BC_CB command.

GS_BROADCAST

Sends a broadcast to all thread siblings of the calling task. Every sibling that has established a broadcast guarded storage control block will load this control block and will be enabled for guarded storage. The broadcast guarded storage control block is consumed; a second broadcast without a refresh of the stored control block with GS_SET_BC_CB will not have any effect.

The gs_cb argument specifies the address of a guarded storage control block structure and is currently used only by the GS_SET_BC_CB command; all other aforementioned commands ignore this argument.

On success, the return value of s390_guarded_storage() is 0.

On error, -1 is returned, and errno is set to indicate the error.

syscall(2)