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Diffstat (limited to 'lib/libc/sys/sigaltstack.2')
-rw-r--r-- | lib/libc/sys/sigaltstack.2 | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/lib/libc/sys/sigaltstack.2 b/lib/libc/sys/sigaltstack.2 new file mode 100644 index 0000000..d9cb273 --- /dev/null +++ b/lib/libc/sys/sigaltstack.2 @@ -0,0 +1,162 @@ +.\" Copyright (c) 1983, 1991, 1992, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" @(#)sigaltstack.2 8.2 (Berkeley) 5/1/95 +.\" $FreeBSD$ +.\" +.Dd May 6, 2010 +.Dt SIGALTSTACK 2 +.Os +.Sh NAME +.Nm sigaltstack +.Nd set and/or get signal stack context +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In signal.h +.Bd -literal +typedef struct { + char *ss_sp; + size_t ss_size; + int ss_flags; +} stack_t; +.Ed +.Ft int +.Fn sigaltstack "const stack_t * restrict ss" "stack_t * restrict oss" +.Sh DESCRIPTION +The +.Fn sigaltstack +system call +allows defining an alternate stack on which signals +are to be processed for the current thread. +If +.Fa ss +is non-zero, +it specifies a pointer to and the size of a +.Em "signal stack" +on which to deliver signals. +When a signal's action indicates its handler +should execute on the signal stack (specified with a +.Xr sigaction 2 +system call), the system checks to see +if the thread is currently executing on that stack. +If the thread 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. +.Pp +An active stack cannot be modified. +.Pp +If +.Dv SS_DISABLE +is set in +.Fa ss_flags , +.Fa ss_sp +and +.Fa ss_size +are ignored and the signal stack will be disabled. +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. +.Pp +If +.Fa oss +is non-zero, the current signal stack state is returned. +The +.Fa ss_flags +field will contain the value +.Dv SS_ONSTACK +if the thread is currently on a signal stack and +.Dv SS_DISABLE +if the signal stack is currently disabled. +.Sh NOTES +The value +.Dv 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. +.Bd -literal -offset indent +if ((sigstk.ss_sp = malloc(SIGSTKSZ)) == NULL) + /* error return */ +sigstk.ss_size = SIGSTKSZ; +sigstk.ss_flags = 0; +if (sigaltstack(&sigstk, NULL) < 0) + perror("sigaltstack"); +.Ed +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 +.Dv 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 +.Dv MINSIGSTKSZ +to their stack requirements to allow for the operating system overhead. +.Pp +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. +.Sh RETURN VALUES +.Rv -std sigaltstack +.Sh ERRORS +The +.Fn sigaltstack +system call +will fail and the signal stack context will remain unchanged +if one of the following occurs. +.Bl -tag -width Er +.It Bq Er EFAULT +Either +.Fa ss +or +.Fa oss +points to memory that is not a valid part of the process +address space. +.It Bq Er EPERM +An attempt was made to modify an active stack. +.It Bq Er EINVAL +The +.Fa ss_flags +field was invalid. +.It Bq Er ENOMEM +Size of alternate stack area is less than or equal to +.Dv MINSIGSTKSZ . +.El +.Sh SEE ALSO +.Xr sigaction 2 , +.Xr setjmp 3 +.Sh HISTORY +The predecessor to +.Fn sigaltstack , +the +.Fn sigstack +system call, appeared in +.Bx 4.2 . |