sigaltstack - set or get signal alternate stack context
const stack_t *ss,
stack_t *oss );
The following function declaration does not conform to current standards
and is supported only for backward compatibility:
stack_t *oss );
Interfaces documented on this reference page conform to industry standards
Refer to the standards(5) reference page for more information about indus-
try standards and associated tags.
ss If valid, specifies a pointer to a structure that indicates what will
be in effect upon return from the call to the sigaltstack function.
oss If not NULL, specifies the pointer to a structure that contains the
alternate signal stack that was in effect prior to the call to the
This function enables another stack area to be defined where signals can be
examined for their execution status and processed. If a signal's action,
specified by the sigaction(2) function, indicates that a signal should exe-
cute on an alternate stack, that signal is examined for its processing
status. A process that is not currently executing on the signal stack is
switched to an alternate stack for the duration of the handler's execution.
The sigaltstack structure is set up as follows:
void *ss_sp /* SVID3 uses caddr_t ss_sp
The values for the fields are:
Signal stack pointer.
Specifies the new stack state and may be set to either SS_DISABLE or
SS_ONSTACK as follows:
+ If ss is not NULL, the new state may be set to SS_DISABLE, which
specifies that the stack is to be disabled and ss_sp and ss_size
are ignored. If SS_DISABLE is not set, the stack will be enabled.
+ If oss is not NULL, the stack state may be either SS_ONSTACK or
SS_DISABLE. The value SS_ONSTACK indicates that the process is
currently executing on the alternate stack and that any attempt to
modify it during execution will fail. The value SS_DISABLE indi-
cates that the current signal stack is disabled.
Specifies the size of the stack.
The value SIGSTKSZ defines the average number of bytes used when allocating
an alternate stack area. The value MINSIGSTKSZ defines the minimum stack
size for a signal handler. When processing an alternate stack size, your
program should include these values in the stack requirement to plan for
the overhead of the operating system.
Upon successful completion, zero (0) is returned. On error, the value -1
is returned and errno is set to indicate the error.
The sigaltstack() function sets errno to the specified values for the fol-
The ss parameter is not a null pointer, and the ss_flags member pointed
to by ss contains flags other than SS_DISABLE.
The size of the alternate stack area is less than MINSIGSTKSZ.
An attempt was made to modify an active stack.
Functions: getcontext(2), sigaction(2)