sigvec.2

来自「<B>Digital的Unix操作系统VAX 4.2源码</B>」· 2 代码 · 共 371 行

.\" SCCSID: @(#)sigvec.2	2.3	6/8/87
.TH sigvec 2 RISC
.ie t .ds d \(dg
.el .ds d \z'|+'
.ie t .ds b \(bu
.el .ds b @
.SH Name
sigvec \- software signal facilities
.SH Syntax
.nf
.B #include <signal.h>
.PP
.B struct sigvec {
.B	void		(*sv_handler)();
.B	sigset_t	sv_mask;
.B	int		sv_flags;
.B };
.PP
.B sigvec(sig, vec, ovec)
.B int sig;
.B struct sigvec *vec, *ovec;
.fi
.SH Description
.NXB "sigvec system call"
.NXB "signal handler" "assigning"
The system defines a set of signals that can be delivered to a process.
Signal delivery resembles the occurrence 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 can specify a
handler to which a signal is delivered, or specify that a signal is to be 
blocked or ignored .
A process can 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 can be changed, on a per-handler basis,
so that signals are taken on a special
signal stack.
.PP
All signals have the same priority.
Signal routines execute with the signal that caused their
invocation blocked, but other signals can occur.
A global signal mask defines the set of signals currently 
blocked from delivery
to a process.  The signal mask for a process is initialized
from that of its parent (normally, 0).  It
can be changed with a
.MS sigblock 2
or
.MS sigsetmask 2
call, or when a signal is delivered to the process.
.PP
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
blocked by the process, 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 later), 
and the signal handler is invoked.  The call to the handler
is arranged so that, if the signal handling routine returns
normally, the process resumes execution in the context
from before the signal's delivery.
If the process wishes to resume in a different context, it
must arrange to restore the previous context itself.
.PP
When a signal is delivered to a process, a new signal mask is
installed for the duration of the process's signal handler
(or until a
.PN sigblock
or
.PN sigsetmask
call is made).
This mask is formed by taking the current signal mask,
adding the signal to be delivered, and ORing
in the signal mask associated with the handler to be invoked.
.PP
The
.PN sigvec
System call assigns a handler for a specific signal.  If
.I vec
is nonzero, it
specifies a handler routine and mask
to be used when delivering the specified signal.
Further, if the SV_ONSTACK bit is set in
.IR sv_flags ,
the system delivers the signal to the process on a signal stack,
specified with 
.MS sigstack 2 .
If 
.I ovec
is nonzero, the previous handling information for the signal
is returned to the user.
.PP
The following is a list of all signals
with names as in the include file 
.PN <signal.h> :
.NXR "sigvec system call" "signal list"
.PP
.nf
.ta \w'SIGVTALRM 'u +\w'15*  'u
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 fcntl(2))
SIGXCPU	24	Cpu time limit exceeded (see setrlimit(2))
SIGXFSZ	25	File size limit exceeded (see setrlimit(2))
SIGVTALRM	26	Virtual time alarm (see setitimer(2))
SIGPROF	27	Profiling timer alarm (see setitimer(2))
SIGWINCH	28.  Window size change
SIGLOST	29	Lock not reclaimed after server recovery
SIGUSR1	30	User-defined signal 1
SIGUSR2	31	User-defined signal 2
SIGCLD		System V name for SIGCHLD
SIGABRT		X/OPEN name for SIGIOT
.fi
.PP
The signals marked with asterisks (*) in this list cause a core image
if not caught or ignored.  Explanations of the meaning of the periods (.)
and plus signs (+) are included in the following paragraph.
.PP
Once a signal handler is installed, it remains installed
until another
.PN sigvec
call is made or an 
.MS execve 2
is performed.
The default action for a signal can be reinstated by setting
.I sv_handler
to SIG_DFL. This default is termination
(with a core image for signals marked with asterisks (*)),
except for signals marked with periods (.) or plus signs (+).
Signals marked with periods (.) are discarded if the action
is SIG_DFL. Signals marked with plus signs (+) cause the process to stop.
If
.I sv_handler
is SIG_IGN, the signal is subsequently ignored,
and pending instances of the signal are discarded.
.PP
If a caught signal occurs
during certain system calls,
the call is normally restarted.
The call can be forced to terminate prematurely with an
EINTR error return, by setting the SV_INTERRUPT bit in
.IR sv_flags .
The affected system calls are
.PN read ,
.PN write ,
or
.PN ioctl
on a slow device (such as a terminal, but not a file),
.PN flock ,
and
.PN wait .
.PP
After a 
.PN fork 
or
.PN vfork ,
the child inherits
all signals, the signal mask, the signal stack,
and the restart/interrupt flags.
.PP
The
.PN execve
system call 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.
.PP
The mask specified in 
.I vec
is not allowed to block SIGKILL, SIGSTOP, or SIGCONT.  This
is done silently by the system.
.PP
The SV_INTERRUPT flag is not available in ULTRIX 2.0 or earlier versions.
Therefore, it should not be used if backward compatibility is needed.
.SH Return Values
A zero (0) value indicates that the call succeeded.  A \-1 return value
indicates an error occurred, and
.I errno
is set to indicated the reason.
.SH Diagnostics
.NXR "sigvec system call" "diagnostics"
The
.PN sigvec
system call
fails and no new signal handler is installed, if one
of the following occurs:
.TP 15
[EFAULT]
Either
.I vec
or 
.I ovec
points to memory that is not a valid part of the process
address space.
.TP 15
[EINVAL]
.I Sig
is not a valid signal number.
.TP 15
[EINVAL]
An attempt is made to ignore or supply a handler for SIGKILL
or SIGSTOP.
.TP 15
[EINVAL]
An attempt is made to ignore SIGCONT (by default SIGCONT
is ignored).
.SH Notes 
The handler routine can be declared:
.EX
void handler(sig, code, scp)
int sig, code;
struct sigcontext *scp;
.EE
Here
.I sig
is the signal number.
MIPS hardware exceptions are mapped to specific signals as defined by
the following table.
.I Code
is a parameter that is either a constant or zero.  The
.I scp
is a pointer to the
.I sigcontext
structure (defined in
.PN <signal.h> ,
that is the context at the time of the signal and is
used to restore the context, if the signal handler returns.
.PP
The following defines the mapping of MIPS hardware exceptions to signals
and codes.  All of these symbols are defined in either
.RI < signal.h >
or
.RI < mips/cpu.h >:
.PP
.ta \w'     User Single Step (used by debuggers)   'u +\w'15*  'u +8n
.nf
.B Hardware exception	Signal	Code
.sp +.5
Integer overflow	SIGFPE	EXC_OV
Segmentation violation	SIGSEGV	SEXC_SEGV
Illegal instruction	SIGILL	EXC_II
Coprocessor unusable	SIGILL	SEXC_CPU
Data bus error	SIGBUS	EXC_DBE
Instruction bus error	SIGBUS	EXC_IBE
Read address error	SIGBUS	EXC_RADE
Write address error	SIGBUS	EXC_WADE
User breakpoint (used by debuggers)	SIGTRAP	BRK_USERBP
Kernel breakpoint (used by prom)	SIGTRAP	BRK_KERNELBP
Taken branch delay emulation 	SIGTRAP	BRK_BD_TAKEN
Not taken branch delay emulation	SIGTRAP	BRK_BD_NOTTAKEN
User single step (used by debuggers)	SIGTRAP	BRK_SSTEPBP
Overflow check	SIGTRAP	BRK_OVERFLOW
Divide by zero check	SIGTRAP	BRK_DIVZERO
Range error check	SIGTRAP	BRK_RANGE
.fi
.PP
When a signal handler is reached, the program counter in the signal context
structure
.RI ( sc_pc )
points at the instruction that caused the exception, as modified by the
.I "branch delay"
bit in the
.I cause
register.
The
.I cause
register at the time of the exception is also saved in the sigcontext
structure
.RI ( sc_cause ).
If the instruction that caused the exception is at a valid user address, it
can be retrieved with the following code sequence:
.EX
if(scp->sc_cause & CAUSE_BD){
    branch_instruction = *(unsigned long *)(scp->sc_pc);
    exception_instruction = *(unsigned long *)(scp->sc_pc + 4);
}
else
    exception_instruction = *(unsigned long *)(scp->sc_pc);
.EE
CAUSE_BD is defined in
.PN <mips/cpu.h> .
.PP
The signal handler can fix the cause of the exception and re-execute the
instruction, emulate the instruction and then step over it, or perform some
nonlocal redirection, such as a
.PN longjump()
or an
.PN exit() .
.PP
If corrective action is performed in the signal handler and the instruction
that caused the exception would then execute without a further exception, the
signal handler simply returns and re-executes the instruction (even when the
.I "branch delay"
bit is set).
.PP
If execution is to continue after stepping over the instruction that caused the
exception, the program counter must be advanced.  If the
.I "branch delay"
bit is set, the program counter is set to the target of the branch. 
Otherwise, it is incremented by four.  
This can be done with the following code sequence:
.EX
if(scp->sc_cause & CAUSE_BD)
    emulate_branch(scp, branch_instruction);
else
    scp->sc_pc += 4;
.EE
.I Emulate_branch()
modifies the program counter value in the sigcontext structure to the target
of the branch instruction.  See
.MS emulate_branch 3
for more details.
.PP
For SIGFPE's generated by floating-point instructions
.RI ( code
== 0) the
.I "floating-point control and status"
register at the time of the exception is also saved in the sigcontext structure
.RI ( sc_fpc_csr ).
This register has the information on which exceptions have occurred.
When a signal handler is entered, the register contains the value at the time
of the exception but with the
.I "exceptions bits"
cleared.
On a return from the signal handler, the exception bits
in the floating-point control and status register are also cleared so
that another SIGFPE will not occur (all other bits are restored from
.IR sc_fpc_csr ).
.PP
For SIGSEGV and SIGBUS errors, the faulting virtual address is saved in
.I sc_badvaddr
in the signal context structure.
.PP
The SIGTRAPs caused by
.PN break
instructions noted in the previous table and all other yet to be defined
.PN break
instructions fill the
.I code
parameter with the first argument to the
.PN break
instruction (bits 25-16 of the instruction).

.SH See Also
kill(1), kill(2), ptrace(2), sigblock(2), sigpause(2), sigsetmask(2),
sigstack(2), setjmp(3), siginterrupt(3), tty(4)
.NXE "sigvec system call"
.NXE "signal handler" "assigning"