sigaltstack(2) [osf1 man page]
sigaltstack(2) System Calls Manual sigaltstack(2) NAME
sigaltstack - set or get signal alternate stack context SYNOPSIS
#include <signal.h> int sigaltstack( const stack_t *ss, stack_t *oss ); The following function declaration does not conform to current standards and is supported only for backward compatibility: #include <sig- nal.h> int sigaltstack( stack_t *ss, stack_t *oss ); STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: sigaltstack(): XPG4-UNIX Refer to the standards(5) reference page for more information about industry standards and associated tags. PARAMETERS
If valid, specifies a pointer to a structure that indicates what will be in effect upon return from the call to the sigaltstack function. 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 sigaltstack function. DESCRIPTION
This function enables another stack area to be defined where signals can be examined for their execution status and processed. If a sig- nal's action, specified by the sigaction(2) function, indicates that a signal should execute 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 dura- tion of the handler's execution. The sigaltstack structure is set up as follows: void *ss_sp /* SVID3 uses caddr_t ss_sp int ss_flags size_t ss_size 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_DIS- ABLE. The value SS_ONSTACK indicates that the process is currently executing on the alternate stack and that any attempt to modify it dur- ing execution will fail. The value SS_DISABLE indicates 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. RETURN VALUES
Upon successful completion, zero (0) is returned. On error, the value -1 is returned and errno is set to indicate the error. ERRORS
The sigaltstack() function sets errno to the specified values for the following conditions: 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. SEE ALSO
Functions: getcontext(2), sigaction(2) Routines: sigsetjmp(3) Files: ucontext(5) Standards: standards(5) sigaltstack(2)
Check Out this Related Man Page
SIGALTSTACK(2) BSD System Calls Manual SIGALTSTACK(2) NAME
sigaltstack -- set and/or get signal stack context LIBRARY
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 dura- tion of the signal handler's execution. An active stack cannot be modified. If SS_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 sig- nals 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 cur- rently on a signal stack and SS_DISABLE if the signal stack is currently disabled. NOTES
The value SIGSTKSZ 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"); An alternative approach is provided for programs with signal handlers that require a specific amount of stack space other than the default size. The value 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 pro- tected 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. BSD
May 6, 2010 BSD