1 GETCONTEXT(2) System Calls GETCONTEXT(2)
2
3 NAME
4 getcontext, setcontext - get and set current user context
5
6 SYNOPSIS
7 #include <ucontext.h>
8
9 int
10 getcontext(ucontext_t *ucp);
11
12 int
13 setcontext(const ucontext_t *ucp);
14
15 DESCRIPTION
16 The getcontext() function initializes the structure pointed to by ucp to
17 the current user context of the calling process. The ucontext_t type
18 that ucp points to defines the user context and includes the contents of
19 the calling process' machine registers, the signal mask, and the current
20 execution stack.
21
22 The setcontext() function restores the user context pointed to by ucp. A
23 successful call to setcontext() does not return; program execution
24 resumes at the point specified by the ucp argument passed to
25 setcontext(). The ucp argument should be created either by a prior call
26 to getcontext(), or by being passed as an argument to a signal handler.
27 If the ucp argument was created with getcontext(), program execution
28 continues as if the corresponding call of getcontext() had just returned.
29 If the ucp argument was created with makecontext(3C), program execution
30 continues with the function passed to makecontext(3C). When that
31 function returns, the process continues as if after a call to
32 setcontext() with the ucp argument that was input to makecontext(3C). If
33 the ucp argument was passed to a signal handler, program execution
34 continues with the program instruction following the instruction
35 interrupted by the signal. If the uc_link member of the ucontext_t
36 structure pointed to by the ucp argument is NULL, then this context is
37 the main context, and the process will exit when this context returns.
38 The effects of passing a ucp argument obtained from any other source are
39 unspecified.
40
41 RETURN VALUES
42 On successful completion, setcontext() does not return and getcontext()
43 returns 0. Otherwise, -1 is returned.
44
45 ERRORS
46 No errors are defined.
47
48 USAGE
49 When a signal handler is executed, the current user context is saved and
50 a new context is created. If the thread leaves the signal handler via
51 longjmp(3C), then it is unspecified whether the context at the time of
52 the corresponding setjmp(3C) call is restored and thus whether future
53 calls to getcontext() will provide an accurate representation of the
54 current context, since the context restored by longjmp(3C) may not
55 contain all the information that setcontext() requires. Signal handlers
56 should use siglongjmp(3C) instead.
57
58 Portable applications should not modify or access the uc_mcontext member
59 of ucontext_t. A portable application cannot assume that context
60 includes any process-wide static data, possibly including errno. Users
61 manipulating contexts should take care to handle these explicitly when
62 required.
63
64 INTERFACE STABILITY
65 Committed
66
67 SEE ALSO
68 sigaction(2), sigaltstack(2), sigprocmask(2), bsd_signal(3C),
69 makecontext(3C), setjmp(3C), sigsetjmp(3C), ucontext.h(3HEAD),
70 attributes(7), standards(7)
71
72 illumos November 24, 2022 illumos
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1 GETCONTEXT(2) System Calls GETCONTEXT(2)
2
3 NAME
4 getcontext, getcontext_extd, setcontext - get and set current user
5 context
6
7 SYNOPSIS
8 #include <ucontext.h>
9
10 int
11 getcontext(ucontext_t *ucp);
12
13 int
14 getcontext_extd(ucontext_t *ucp, uint32_t flags);
15
16 int
17 setcontext(const ucontext_t *ucp);
18
19 DESCRIPTION
20 The getcontext() function initializes the structure pointed to by ucp to
21 the current user context of the calling process. The ucontext_t type
22 that ucp points to defines the user context and includes the contents of
23 the calling process' machine registers, the signal mask, and the current
24 execution stack.
25
26 The ucontext_t structure is a part of the system ABI. However, most
27 architectures have added additional register states such as the extended
28 vector and floating point registers that are not part of that. To
29 facilitate getting that state (such as the x86 xsave area) the
30 getcontext_extd() function exists. Once called, the context will be
31 initialized and is suitable for use in other context operations just as
32 though one had called getcontext().
33
34 Unlike the getcontext() function, getcontext_extd() assumes that callers
35 have previously initialized ucp and thus it treats additional members
36 (such as the uc_xsave member on x86) as potentially valid. To allow for
37 all extended states to be copied out, ucp must be allocated with
38 ucontext_alloc(3C). Otherwise whether it is declared on the stack, as
39 global data, allocated dynamically, or part of a structure, ucp must be
40 zeroed through a call to bzero(3C) or memset(3C) prior to calling
41 getcontext_extd(). Improper initialization can lead to memory safety
42 bugs, making it critical that this is done.
43
44 The flags member must be zero and is present to allow for what is copied
45 out to change in the future. This indicates that the system should
46 attempt to copy out all extended states, though if the ucontext_t was not
47 allocated with ucontext_alloc(3C), some extended states may not be.
48
49 The setcontext() function restores the user context pointed to by ucp. A
50 successful call to setcontext() does not return; program execution
51 resumes at the point specified by the ucp argument passed to
52 setcontext(). The ucp argument should be created either by a prior call
53 to getcontext(), or by being passed as an argument to a signal handler.
54 If the ucp argument was created with getcontext(), program execution
55 continues as if the corresponding call of getcontext() had just returned.
56 If the ucp argument was created with makecontext(3C), program execution
57 continues with the function passed to makecontext(3C). When that
58 function returns, the process continues as if after a call to
59 setcontext() with the ucp argument that was input to makecontext(3C). If
60 the ucp argument was passed to a signal handler, program execution
61 continues with the program instruction following the instruction
62 interrupted by the signal. If the uc_link member of the ucontext_t
63 structure pointed to by the ucp argument is NULL, then this context is
64 the main context, and the process will exit when this context returns.
65 The effects of passing a ucp argument obtained from any other source are
66 unspecified.
67
68 RETURN VALUES
69 On successful completion, setcontext() does not return and getcontext()
70 and getcontext_extd() returns 0. Otherwise, -1 is returned.
71
72 ERRORS
73 No errors are defined for getcontext() or setcontext().
74
75 The getcontext_extd() function only sets errno in some circumstances when
76 it fails. The function may fail if:
77
78 EINVAL flags had invalid values.
79
80 USAGE
81 When a signal handler is executed, the current user context is saved and
82 a new context is created. If the thread leaves the signal handler via
83 longjmp(3C), then it is unspecified whether the context at the time of
84 the corresponding setjmp(3C) call is restored and thus whether future
85 calls to getcontext() will provide an accurate representation of the
86 current context, since the context restored by longjmp(3C) may not
87 contain all the information that setcontext() requires. Signal handlers
88 should use siglongjmp(3C) instead.
89
90 Portable applications should not modify or access the uc_mcontext member
91 of ucontext_t. A portable application cannot assume that context
92 includes any process-wide static data, possibly including errno. Users
93 manipulating contexts should take care to handle these explicitly when
94 required.
95
96 INTERFACE STABILITY
97 Committed
98
99 SEE ALSO
100 sigaction(2), sigaltstack(2), sigprocmask(2), bsd_signal(3C),
101 makecontext(3C), setjmp(3C), sigsetjmp(3C), ucontext_alloc(3C),
102 ucontext.h(3HEAD), attributes(7), standards(7)
103
104 illumos January 24, 2022 illumos
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