NAME
sigaltstack — set and/or get signal stack contextLIBRARY
Standard C Library (libc, -lc)SYNOPSIS
#include <signal.h>
typedef struct {
char *ss_sp;
size_t ss_size;
int ss_flags;
} stack_t;
int
sigaltstack(const stack_t * restrict ss, stack_t * restrict oss);
DESCRIPTION
The sigaltstack() system call allows defining an alternate stack on which signals are to be processed for the current thread. If ss is non-zero, it specifies a pointer to and the size of a signal stack on which to deliver signals. When a signal's action indicates its handler should execute on the signal stack (specified with a sigaction(2) system call), the system checks to see if the thread is currently executing on that stack. If the thread is not currently executing on the signal stack, the system arranges a switch to the signal stack for the duration of the signal handler's execution. An active stack cannot be modified. IfSS_DISABLE is set in
ss_flags,
ss_sp and
ss_size are ignored and the signal stack will
be disabled. A disabled stack will cause all signals to be taken on the
regular user stack. If the stack is later re-enabled then all signals that
were specified to be processed on an alternate stack will resume doing so.
If oss is non-zero, the current signal stack
state is returned. The ss_flags field will
contain the value SS_ONSTACK if the thread
is currently on a signal stack and
SS_DISABLE if the signal stack is currently
disabled.
NOTES
The valueSIGSTKSZ is defined to be the
number of bytes/chars that would be used to cover the usual case when
allocating an alternate stack area. The following code fragment is typically
used to allocate an alternate stack.
if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL)
/* error return */
sigstk.ss_size = SIGSTKSZ;
sigstk.ss_flags = 0;
if (sigaltstack(&sigstk, NULL) < 0)
perror("sigaltstack");
MINSIGSTKSZ is defined to be the
number of bytes/chars that is required by the operating system to implement
the alternate stack feature. In computing an alternate stack size, programs
should add MINSIGSTKSZ to their stack
requirements to allow for the operating system overhead.
Signal stacks are automatically adjusted for the direction of stack growth and
alignment requirements. Signal stacks may or may not be protected by the
hardware and are not ``grown'' automatically as is done for the normal stack.
If the stack overflows and this space is not protected unpredictable results
may occur.
RETURN VALUES
The sigaltstack() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.ERRORS
The sigaltstack() system call will fail and the signal stack context will remain unchanged if one of the following occurs.- [
EFAULT] - Either ss or oss points to memory that is not a valid part of the process address space.
- [
EPERM] - An attempt was made to modify an active stack.
- [
EINVAL] - The ss_flags field was invalid.
- [
ENOMEM] - Size of alternate stack area is less than or equal to
MINSIGSTKSZ.
SEE ALSO
sigaction(2), setjmp(3)HISTORY
The predecessor to sigaltstack(), the sigstack() system call, appeared in 4.2BSD.| May 6, 2010 | Debian |