svn commit: r207734 - head/lib/libc/sys
Jilles Tjoelker
jilles at FreeBSD.org
Thu May 6 22:06:15 UTC 2010
Author: jilles
Date: Thu May 6 22:06:14 2010
New Revision: 207734
URL: http://svn.freebsd.org/changeset/base/207734
Log:
sigaltstack(2): document some modernizations:
* un-document 'struct sigaltstack' tag for stack_t as this is BSD-specific;
this doesn't seem useful enough to document as such
* alternate stacks are per thread, not per process
* update error codes to what the kernel does and POSIX requires
MFC after: 1 week
Modified:
head/lib/libc/sys/sigaltstack.2
Modified: head/lib/libc/sys/sigaltstack.2
==============================================================================
--- head/lib/libc/sys/sigaltstack.2 Thu May 6 21:57:38 2010 (r207733)
+++ head/lib/libc/sys/sigaltstack.2 Thu May 6 22:06:14 2010 (r207734)
@@ -28,7 +28,7 @@
.\" @(#)sigaltstack.2 8.2 (Berkeley) 5/1/95
.\" $FreeBSD$
.\"
-.Dd May 1, 1995
+.Dd May 6, 2010
.Dt SIGALTSTACK 2
.Os
.Sh NAME
@@ -39,7 +39,7 @@
.Sh SYNOPSIS
.In signal.h
.Bd -literal
-typedef struct sigaltstack {
+typedef struct {
char *ss_sp;
size_t ss_size;
int ss_flags;
@@ -51,25 +51,25 @@ typedef struct sigaltstack {
The
.Fn sigaltstack
system call
-allows users to define an alternate stack on which signals
-are to be processed.
+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,
-and tells the system if the process is currently executing
-on that 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 process is currently executing on that stack.
-If the process is not currently executing on the signal stack,
+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
@@ -78,12 +78,6 @@ is set in
and
.Fa ss_size
are ignored and the signal stack will be disabled.
-Trying to disable an active stack will cause
-.Fn sigaltstack
-to return -1 with
-.Va errno
-set to
-.Er 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
@@ -96,7 +90,7 @@ The
.Fa ss_flags
field will contain the value
.Dv SS_ONSTACK
-if the process is currently on a signal stack and
+if the thread is currently on a signal stack and
.Dv SS_DISABLE
if the signal stack is currently disabled.
.Sh NOTES
@@ -146,8 +140,12 @@ 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
-An attempt was made to disable an active stack.
+The
+.Fa ss_flags
+field was invalid.
.It Bq Er ENOMEM
Size of alternate stack area is less than or equal to
.Dv MINSIGSTKSZ .
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