SIGVEC(2) UNIX Programmer's Manual SIGVEC(2) NAME sigvec - software signal facilities SYNOPSIS #include struct sigvec { int (*sv_handler)(); long sv_mask; int sv_flags; }; sigvec(sig, vec, ovec) int sig; struct sigvec *vec, *ovec; DESCRIPTION This interface has been made obsolete sigaction(2). The system defines a set of signals that may be delivered to a process. Signal delivery resembles the occurence of a hardware interrupt: the signal is blocked from further occurrence, the current process context is saved, and a new one is built. A process may specify a _h_a_n_d_l_e_r to which a signal is delivered, or specify that a signal is to be _b_l_o_c_k_e_d or _i_g_n_o_r_e_d. A process may also specify that a default action is to be taken by the system when a signal occurs. Normally, signal handlers execute on the current stack of the process. This may be changed, on a per-handler basis, so that signals are taken on a special _s_i_g_n_a_l _s_t_a_c_k. All signals have the same _p_r_i_o_r_i_t_y. Signal routines execute with the signal that caused their invocation _b_l_o_c_k_e_d, but other signals may yet occur. A global _s_i_g_n_a_l _m_a_s_k defines the set of signals currently blocked from delivery to a pro- cess. The signal mask for a process is initialized from that of its parent (normally 0). It may be changed with a _s_i_g_b_l_o_c_k(2) or _s_i_g_s_e_t_m_a_s_k(2) call, or when a signal is delivered to the process. When a signal condition arises for a process, the signal is added to a set of signals pending for the process. If the signal is not currently _b_l_o_c_k_e_d by the process then it is delivered to the process. When a signal is delivered, the current state of the process is saved, a new signal mask is calculated (as described below), and the signal handler is invoked. The call to the handler is arranged so that if the signal handling routine returns normally the process will resume execution in the context from before the signal's delivery. If the process wishes to resume in a different context, then it must arrange to restore the previous con- text itself. Printed 11/26/99 September 3, 1997 1 SIGVEC(2) UNIX Programmer's Manual SIGVEC(2) When a signal is delivered to a process a new signal mask is installed for the duration of the process' signal handler (or until a _s_i_g_b_l_o_c_k or _s_i_g_s_e_t_m_a_s_k call is made). This mask is formed by taking the current signal mask, adding the sig- nal to be delivered, and _o_r'ing in the signal mask associ- ated with the handler to be invoked. _S_i_g_v_e_c assigns a handler for a specific signal. If _v_e_c is non-zero, it specifies a handler routine and mask to be used when delivering the specified signal. Further, if the SV_ONSTACK bit is set in _s_v__f_l_a_g_s, the system will deliver the signal to the process on a _s_i_g_n_a_l _s_t_a_c_k, specified with _s_i_g_s_t_a_c_k(2). If _o_v_e_c is non-zero, the previous handling information for the signal is returned to the user. The following is a list of all signals with names as in the include file <_s_i_g_n_a_l._h>: SIGHUP 1 hangup SIGINT 2 interrupt SIGQUIT 3* quit SIGILL 4* illegal instruction SIGTRAP 5* trace trap SIGIOT 6* IOT instruction SIGEMT 7* EMT instruction SIGFPE 8* floating point exception SIGKILL 9 kill (cannot be caught, blocked, or ignored) SIGBUS 10* bus error SIGSEGV 11* segmentation violation SIGSYS 12* bad argument to system call SIGPIPE 13 write on a pipe with no one to read it SIGALRM 14 alarm clock SIGTERM 15 software termination signal SIGURG 16@ urgent condition present on socket SIGSTOP 17'|+'stop (cannot be caught, blocked, or ignored) SIGTSTP 18'|+'stop signal generated from keyboard SIGCONT 19@ continue after stop (cannot be blocked) SIGCHLD 20@ child status has changed SIGTTIN 21'|+'background read attempted from control terminal SIGTTOU 22'|+'background write attempted to control terminal SIGIO 23@ i/o is possible on a descriptor (see _f_c_n_t_l(2)) SIGXCPU 24 cpu time limit exceeded (see _s_e_t_r_l_i_m_i_t(2)) SIGXFSZ 25 file size limit exceeded (see _s_e_t_r_l_i_m_i_t(2)) SIGVTALRM 26 virtual time alarm (see _s_e_t_i_t_i_m_e_r(2)) SIGPROF 27 profiling timer alarm (see _s_e_t_i_t_i_m_e_r(2)) SIGWINCH 28@ window size change SIGUSR1 30 user defined signal 1 SIGUSR2 31 user defined signal 2 The starred signals in the list above cause a core image if not caught or ignored. Printed 11/26/99 September 3, 1997 2 SIGVEC(2) UNIX Programmer's Manual SIGVEC(2) Once a signal handler is installed, it remains installed until another _s_i_g_v_e_c call is made, or an _e_x_e_c_v_e(2) is per- formed. The default action for a signal may be reinstated by setting _s_v__h_a_n_d_l_e_r to SIG_DFL; this default is termina- tion (with a core image for starred signals) except for sig- nals marked with @ or '|+'. Signals marked with @ are dis- carded if the action is SIG_DFL; signals marked with '|+' cause the process to stop. If _s_v__h_a_n_d_l_e_r is SIG_IGN the signal is subsequently ignored, and pending instances of the signal are discarded. If a caught signal occurs during certain system calls, the call is normally restarted. The call can be forced to ter- minate prematurely with an EINTR error return by setting the SV_INTERRUPT bit in _s_v__f_l_a_g_s. The affected system calls are _r_e_a_d(2) or _w_r_i_t_e(2) on a slow device (such as a terminal; but not a file) and during a _w_a_i_t(2). After a _f_o_r_k(2) or _v_f_o_r_k(2) the child inherits all signals, the signal mask, the signal stack, and the restart/interrupt flags. _E_x_e_c_v_e(2) resets all caught signals to default action and resets all signals to be caught on the user stack. Ignored signals remain ignored; the signal mask remains the same; signals that interrupt system calls continue to do so. NOTES The mask specified in _v_e_c is not allowed to block SIGKILL, SIGSTOP, or SIGCONT. This is done silently by the system. The SV_INTERRUPT flag is not available in 4.2BSD, hence it should not be used if backward compatibility is needed. RETURN VALUE A 0 value indicated that the call succeeded. A -1 return value indicates an error occurred and _e_r_r_n_o is set to indi- cated the reason. ERRORS _S_i_g_v_e_c will fail and no new signal handler will be installed if one of the following occurs: [EFAULT] Either _v_e_c or _o_v_e_c points to memory that is not a valid part of the process address space. [EINVAL] _S_i_g is not a valid signal number. [EINVAL] An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP. Printed 11/26/99 September 3, 1997 3 SIGVEC(2) UNIX Programmer's Manual SIGVEC(2) [EINVAL] An attempt is made to ignore SIGCONT (by default SIGCONT is ignored). SEE ALSO kill(1), ptrace(2), kill(2), sigblock(2), sigsetmask(2), sigpause(2), sigstack(2), sigvec(2), setjmp(3), siginter- rupt(3), tty(4) NOTES (VAX-11) The handler routine can be declared: handler(sig, code, scp) int sig, code; struct sigcontext *scp; Here _s_i_g is the signal number, into which the hardware faults and traps are mapped as defined below. _C_o_d_e is a parameter that is either a constant as given below or, for compatibility mode faults, the code provided by the hardware (Compatibility mode faults are distinguished from the other SIGILL traps by having PSL_CM set in the psl). _S_c_p is a pointer to the _s_i_g_c_o_n_t_e_x_t structure (defined in <_s_i_g_n_a_l._h>), used to restore the context from before the signal. The following defines the mapping of hardware traps to sig- nals and codes. All of these symbols are defined in <_s_i_g_n_a_l._h>: Hardware condition Signal Code Arithmetic traps: Integer overflow SIGFPE FPE_INTOVF_TRAP Integer division by zero SIGFPE FPE_INTDIV_TRAP Floating overflow trap SIGFPE FPE_FLTOVF_TRAP Floating/decimal division by zero SIGFPE FPE_FLTDIV_TRAP Floating underflow trap SIGFPE FPE_FLTUND_TRAP Decimal overflow trap SIGFPE FPE_DECOVF_TRAP Subscript-range SIGFPE FPE_SUBRNG_TRAP Floating overflow fault SIGFPE FPE_FLTOVF_FAULT Floating divide by zero fault SIGFPE FPE_FLTDIV_FAULT Floating underflow fault SIGFPE FPE_FLTUND_FAULT Length access control SIGSEGV Protection violation SIGBUS Reserved instruction SIGILL ILL_RESAD_FAULT Customer-reserved instr. SIGEMT Reserved operand SIGILL ILL_PRIVIN_FAULT Reserved addressing SIGILL ILL_RESOP_FAULT Trace pending SIGTRAP Bpt instruction SIGTRAP Compatibility-mode SIGILL hardware supplied code Chme SIGSEGV Chms SIGSEGV Printed 11/26/99 September 3, 1997 4 SIGVEC(2) UNIX Programmer's Manual SIGVEC(2) Chmu SIGSEGV NOTES (PDP-11) The handler routine can be declared: handler(sig, code, scp) int sig, code; struct sigcontext *scp; Here _s_i_g is the signal number, into which the hardware faults and traps are mapped as defined below. _C_o_d_e is a parameter that is a constant as given below. _S_c_p is a pointer to the _s_i_g_c_o_n_t_e_x_t structure (defined in <_s_i_g_n_a_l._h>), used to restore the context from before the signal. The following defines the mapping of hardware traps to sig- nals and codes. All of these symbols are defined in <_s_i_g_n_a_l._h>: Hardware condition Signal Code Arithmetic traps: Floating overflow trap SIGFPE FPE_FLTOVF_TRAP Floating/decimal division by zero SIGFPE FPE_FLTDIV_TRAP Floating underflow trap SIGFPE FPE_FLTUND_TRAP Decimal overflow trap SIGFPE FPE_DECOVF_TRAP Illegal return code SIGFPE FPE_CRAZY Bad op code SIGFPE FPE_OPCODE_TRAP Bad operand SIGFPE FPE_OPERAND_TRAP Maintenance trap SIGFPE FPE_MAINT_TRAP Length access control SIGSEGV Protection violation (odd address) SIGBUS Reserved instruction SIGILL ILL_RESAD_FAULT Customer-reserved instr. SIGEMT Trace pending SIGTRAP Bpt instruction SIGTRAP The handler routine must save any registers it uses and restore them before returning. On the PDP-11, the kernel saves _r_0 and _r_1 before calling the handler routine, but expect the handler to save any other registers it uses. The standard entry code generated by the C compiler for handler routines written in C automatically saves the remaining gen- eral registers, but floating point registers are _n_o_t saved. As a result there is currently no [standard] method for a handler routine written in C to perform floating point operations without blowing the interrupted program out of the water. BUGS This manual page is still confusing. Printed 11/26/99 September 3, 1997 5