s390_guarded_storage(2)

1s390_guarded_storage(2)       System Calls Manual      s390_guarded_storage(2)
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NAME

6       s390_guarded_storage  -  operations with z/Architecture guarded storage
7       facility
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LIBRARY

10       Standard C library (libc, -lc)
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SYNOPSIS

13       #include <asm/guarded_storage.h> /* Definition of GS_* constants */
14       #include <sys/syscall.h>         /* Definition of SYS_* constants */
15       #include <unistd.h>
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17       int syscall(SYS_s390_guarded_storage, int command,
18                   struct gs_cb *gs_cb);
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20       Note: glibc provides no wrapper for s390_guarded_storage(), necessitat‐
21       ing the use of syscall(2).
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DESCRIPTION

24       The  s390_guarded_storage()  system call enables the use of the Guarded
25       Storage Facility (a  z/Architecture-specific  feature)  for  user-space
26       processes.
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28       The  guarded storage facility is a hardware feature that allows marking
29       up to 64 memory regions (as of z14) as guarded; reading a pointer  with
30       a  newly  introduced  "Load  Guarded"  (LGG) or "Load Logical and Shift
31       Guarded" (LLGFSG) instructions will cause a range check on  the  loaded
32       value and invoke a (previously set up) user-space handler if one of the
33       guarded regions is affected.
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35       The command argument indicates which function to perform.  The  follow‐
36       ing commands are supported:
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38       GS_ENABLE
39              Enable  the  guarded storage facility for the calling task.  The
40              initial content of the guarded storage control block will be all
41              zeros.   After  enablement,  user-space  code  can use the "Load
42              Guarded   Storage   Controls"   (LGSC)   instruction   (or   the
43              load_gs_cb()  function wrapper provided in the asm/guarded_stor‐
44              age.h header) to load an arbitrary control block.  While a  task
45              is enabled, the kernel will save and restore the calling content
46              of the guarded storage registers on context switch.
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48       GS_DISABLE
49              Disables the use of the guarded storage facility for the calling
50              task.   The kernel will cease to save and restore the content of
51              the guarded storage  registers,  the  task-specific  content  of
52              these registers is lost.
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54       GS_SET_BC_CB
55              Set  a  broadcast  guarded storage control block to the one pro‐
56              vided in the gs_cb argument.  This is called per thread and  as‐
57              sociates a specific guarded storage control block with the call‐
58              ing task.  This control block will be used in the broadcast com‐
59              mand GS_BROADCAST.
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61       GS_CLEAR_BC_CB
62              Clears the broadcast guarded storage control block.  The guarded
63              storage control block will no longer have the association estab‐
64              lished by the GS_SET_BC_CB command.
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66       GS_BROADCAST
67              Sends  a  broadcast  to all thread siblings of the calling task.
68              Every sibling that has established a broadcast  guarded  storage
69              control  block  will load this control block and will be enabled
70              for guarded storage.   The  broadcast  guarded  storage  control
71              block  is  consumed; a second broadcast without a refresh of the
72              stored control block with GS_SET_BC_CB will not have any effect.
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74       The gs_cb argument specifies the address of a guarded  storage  control
75       block structure and is currently used only by the GS_SET_BC_CB command;
76       all other aforementioned commands ignore this argument.
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RETURN VALUE

79       On success, the return value of s390_guarded_storage() is 0.
80
81       On error, -1 is returned, and errno is set to indicate the error.
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ERRORS

84       EFAULT command was GS_SET_BC_CB and the copying of the guarded  storage
85              control  block  structure  pointed  by  the  gs_cb  argument has
86              failed.
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88       EINVAL The value provided in the command argument was not valid.
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90       ENOMEM command was one of GS_ENABLE or GS_SET_BC_CB, and the allocation
91              of a new guarded storage control block has failed.
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93       EOPNOTSUPP
94              The guarded storage facility is not supported by the hardware.
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STANDARDS

97       Linux on s390.
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HISTORY

100       Linux 4.12.  System z14.
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NOTES

103       The  description of the guarded storage facility along with related in‐
104       structions and Guarded Storage Control Block and Guarded Storage  Event
105       Parameter  List structure layouts is available in "z/Architecture Prin‐
106       ciples of Operations" beginning from the twelfth edition.
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108       The gs_cb structure has a field gsepla (Guarded Storage Event Parameter
109       List Address), which is a user-space pointer to a Guarded Storage Event
110       Parameter List structure (that contains the address  of  the  aforemen‐
111       tioned  event  handler in the gseha field), and its layout is available
112       as a gs_epl structure  type  definition  in  the  asm/guarded_storage.h
113       header.
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