SIGALTSTACK(2) | System Calls Manual | SIGALTSTACK(2) |
typedef struct sigaltstack { void *ss_sp; size_t ss_size; int ss_flags; } stack_t;
If SS_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 alternative 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 process is currently on a signal stack and SS_DISABLE if the signal stack is currently disabled.
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 alternative stack feature. In computing an alternative 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.
March 2, 2012 | NetBSD 7.2 |