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nostk(2) [bsd man page]

NOSTK(2)							System Calls Manual							  NOSTK(2)

nostk - allow process to manage its own stack (2BSD) SYNOPSYS
Nostk informs the system that the process wishes to manage its own stack. The system releases the stack segment(s) it has reserved, making them available for allocation (via brk(2)) by the user. C programs should use nostk only with great caution and understanding of the C language calling and stack conventions. It is most useful for assembler programs that want to use the entire available address space. SEE ALSO
stack(5) BUGS
Nostk is unique to the PDP-11 and 2BSD; its use is discouraged. 3rd Berkeley Distribution June 24, 1987 NOSTK(2)

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SIGALTSTACK(2)						      BSD System Calls Manual						    SIGALTSTACK(2)

sigaltstack -- set and/or get signal stack context SYNOPSIS
#include <sys/types.h> #include <signal.h> struct sigaltstack { char *ss_sp; int ss_size; int ss_flags; }; int sigaltstack(const struct sigaltstack *ss, struct sigaltstack *oss); DESCRIPTION
Sigaltstack() allows users to define an alternate stack on which signals are to be processed. If ss is non-zero, it specifies a pointer to and the size of a signal stack on which to deliver signals, and tells the system if the process is currently executing on that stack. When a signal's action indicates its handler should execute on the signal stack (specified with a sigaction(2) call), the system checks to see if the process is currently executing on that stack. If the process 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. If SA_DISABLE is set in ss_flags, ss_sp and ss_size are ignored and the signal stack will be disabled. Trying to disable an active stack will cause sigaltstack to return -1 with errno set to EINVAL. 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 SA_ONSTACK if the process is cur- rently on a signal stack and SA_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,0) < 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
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error. ERRORS
Sigstack() 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. [EINVAL] An attempt was made to disable an active stack. [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. 4.2 Berkeley Distribution June 4, 1993 4.2 Berkeley Distribution

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