sigvec(2) DG/UX R4.11MU05 sigvec(2)
NAME
sigvec - specify what to do upon presentation of a signal
SYNOPSIS
#include <signal.h>
int sigvec (signalnumber, newsignalvector, oldsignalvector)
int signalnumber;
struct sigvec * newsignalvector;
struct sigvec * oldsignalvector;
where:
signalnumber Any of the valid signals except SIGKILL or
SIGSTOP (see signal.h for a complete list)
newsignalvector NULL or address of new handler specifier
oldsignalvector NULL or address of old handler specifier
DESCRIPTION
Sigvec is used to install a new handler and retrieve the previous
handler for signal signalnumber. A handler for the signal is
optionally installed using the newsignalvector parameter. If
newsignalvector is NULL, the handler remains unchanged. Otherwise,
newsignalvector is installed. The previous handler for the signal
may be obtained by the oldsignalvector parameter. If
oldsignalvector is NULL, the previous handler is not returned.
Otherwise, the previous handler information is stored in the location
pointed to by oldsignalvector.
A signal handler has three components: a set of flags (svflags), a
signal mask (svmask), and an action (svhandler).
Each signal handler may choose to execute on either the current stack
of the calling process or on a special signal stack. The process
must have previously defined the signal stack using sigstack. The
handler's stack choice is indicated by a flag in svflags. Setting
the flag SV_ONSTACK chooses the signal stack of the calling process;
otherwise the current stack is used. The stack address is chosen
when the signal is presented. Thus, subsequent sigstack operations
may redirect the handler's signal stack.
The handler's signal mask is an additional set of signals that are to
be blocked from presentation while the signal is being handled. The
set of signals that are blocked while the signal is being handled is
the union of the handler's signal mask, the signal that occurred, and
the process's current set of blocked signals.
Signal s is represented by the value sigmask(s) in svmask.
The handler's action chooses one of three ways to handle the receipt
of a signal. newsignalvector.svhandler may be assigned one of the
values: SIG_DFL, SIG_IGN, or a function address. The actions
prescribed by these values are as follows:
SIG_DFL Default signal action.
The process's signal action vector entry for signalnumber
is set to `default'.
When the signal signalnumber is sent to the process, it
may be pended depending on the state of the blocked signal
vector. When the signal is presented to the process, it
will cause the process to either terminate, stop, ignore
the signal, or terminate with a core dump depending on the
signal's type (see signal.h).
If a core dump is indicated, the receiving process must
have adequate permission to do so.
SIG_IGN Ignore signal.
The process's signal action vector entry for signalnumber
is set to `ignore'.
When the signal signalnumber is sent to the process, it
may be pended depending on the state of the blocked signal
vector. When the signal is presented to the process, it
will be discarded.
SIGKILL and SIGSTOP cannot be ignored.
address Catch signal.
The process's signal action vector entry for signalnumber
is set to `catch'.
When the signal signalnumber is sent to the process, it
may be pended depending on the state of the blocked signal
vector. When the signal is presented to the process, it
will cause the signal handler specified by action to be
invoked. Upon invocation of the signal handler the first
argument to the handler function will always be the number
of the caught signal. Other signal state information may
be passed to the handler via arguments depending upon the
current software development environment. See siginfo(5)
and sde-target(1) for details.
The following attributes are set for the signal action
vector entry for signalnumber:
· The signal mask addend is set to the union of
newsignalvector.svmask and signalnumber. These
signals are added to the blocked signal vector for
the duration of the signal handler's invocation.
· The signal stack choice is set based on the flag
SV_ONSTACK. This may cause a stack switch to take
place for the duration of the signal handler's
invocation.
· The new signal action is set to `unchanged'. The
occurrence of multiple signals will not cause the
loss of signals or process termination.
· The restart system call choice is set based on the
flag SV_INTERRUPT. If the flag is set, system calls
interrupted by signal signalnumber will be be
terminated with errno set to EINTR rather than being
restarted. If the flag is not set, restartable
system call will be transparently restarted when the
signal handler returns.
SIGKILL and SIGSTOP cannot be caught.
After a fork, the child process inherits all software signal
structures, except that the pending signal vector is cleared.
Exec modifies the software signal structures in the following manner:
1) The signal action for signals set to `catch' is changed to
`default'. 2) The signal stack context is discarded. 3) All other
software signal structures are unchanged.
The mask specified in newsignalvector is not allowed to block
SIGKILL or SIGSTOP. This is done silently by the system.
Sigvec will fail and the signal handler will be unchanged if an error
occurs.
ACCESS CONTROL
No access is required to install a signal handler.
The receiving process is granted permission to produce a core dump
file provided
· the effective-user-id and the real-user-id of the receiving
process are equal, and
· the receiving process has adequate file system permission to
create or rewrite the core dump file.
RETURN VALUE
0 Completed successfully.
-1 An error occurred. errno is set to indicate the error.
DIAGNOSTICS
Errno may be set to one of the following error codes:
EFAULT Either newsignalvector or oldsignalvector point to
memory which is not a valid part of the process address
space.
EINVAL Signalnumber is not a valid signal number.
EINVAL An attempt is made to ignore or supply a handler for
SIGKILL or SIGSTOP.
SEE ALSO
kill(1), kill(2), ptrace(2), sigblock(2), sigpause(2), sigsetmask(2),
sigstack(2), setjmp(3C), sde-target(1).
Licensed material--property of copyright holder(s)