Originální popis anglicky:
sigaltstack - set and/or get signal stack context
Návod, kniha: Linux Programmer's Manual
#include <signal.h>
int sigaltstack(const stack_t *ss, stack_t
*oss);
sigaltstack allows a process to define a new alternate signal stack
and/or retrieve the state of an existing alternate signal stack. An alternate
signal stack is used during the execution of a signal handler if the
establishment of that handler (see
sigaction(2)) requested it.
The normal sequence of events for using an alternate signal stack is the
following:
- 1.
- Allocate an area of memory to be used for the alternate
signal stack.
- 2.
- Use sigaltstack to inform the system of the
existence and location of the alternate signal stack.
- 3.
- When establishing a signal handler using sigaction,
inform the system that the signal handler should be executed on the
alternate signal stack by specifying the SA_ONSTACK flag.
The
ss argument is used to specify a new alternate signal stack, while
the
oss argument is used to retrieve information about the currently
established signal stack. If we are interested in performing just one of these
tasks then the other argument can be specified as NULL. Each of these
arguments is a structure of the following type:
typedef struct {
void *ss_sp; /* Base address of stack */
int ss_flags; /* Flags */
size_t ss_size; /* Number of bytes in stack */
} stack_t;
To establish a new alternate signal stack,
ss.ss_flags is set to zero,
and
ss.sp_sp and
ss.ss_size specify the starting address and
size of the stack. The constant
SIGSTKSZ is defined to be large enough
to cover the usual size requirements for an alternate signal stack, and the
constant
MINSIGSTKSZ defines the minimum size required to execute a
signal handler.
To disable an existing stack, specify
ss.ss_flags as
SS_DISABLE.
In this case, the remaining fields in
ss are ignored.
If
oss is not NULL, then it is used to return information about the
alternate signal stack which was in effect prior to the call to
sigaltstack. The
oss.ss_sp and
oss.ss_size fields return
the starting address and size of that stack. The
oss.ss_flags may
return either of the following values:
- SS_ONSTACK
- The process is currently executing on the alternate signal
stack. (Note that it is not possible to change the alternate signal stack
if the process is currently executing on it.)
- SS_DISABLE
- The alternate signal stack is currently disabled.
sigaltstack returns 0 on success, or -1 on failure with
errno set
to indicate the error.
- EFAULT
- Either ss or oss is not NULL and points to an
area outside of the process's address space.
- EINVAL
- ss is not NULL and the ss_flags field
contains a non-zero value other than SS_DISABLE.
- ENOMEM
- The specified size of the new alternate signal stack (
ss.ss_size) was less than MINSTKSZ.
- EPERM
- An attempt was made to change the alternate signal stack
while it was active (i.e., the process was already executing on the
current alternate signal stack).
The following code segment demonstrates the use of
sigaltstack:
stack_t ss;
ss.ss_sp = malloc(SIGSTKSZ);
if (ss.ss_sp == NULL)
/* Handle error */;
ss.ss_size = SIGSTKSZ;
ss.ss_flags = 0;
if (sigaltstack(&ss, NULL) == -1)
/* Handle error */;
Establishing an alternate signal stack is useful if a process expects that it
may exhaust its standard stack. This may occur, for example, because the stack
grows so large that it encounters the upwardly growing heap, or it reaches a
limit established by a call to
setrlimit(RLIMIT_STACK, &rlim). If
the standard stack is exhausted, the kernel sends the process a
SIGSEGV
signal. In these circumstances the only way to catch this signal is on an
alternate signal stack.
On most hardware architectures supported by Linux, stacks grow downwards.
sigaltstack automatically takes account of the direction of stack
growth.
Functions called from a signal handler executing on an alternate signal stack
will also use the alternate signal stack. (This also applies to any handlers
invoked for other signals while the process is executing on the alternate
signal stack.) Unlike the standard stack, the system does not automatically
extend the alternate signal stack. Exceeding the allocated size of the
alternate signal stack will lead to unpredictable results.
A successful call to
execve removes any existing alternate signal stack.
sigaltstack supersedes the older
sigstack call. For backwards
compatibility, glibc also provides
sigstack. All new applications
should be written using
sigaltstack.
BSD 4.2 had a
sigstack() system call. It used a slightly different
struct, and had as major disadvantage that the caller had to know the
direction of stack growth.
SUSv2, SVr4, POSIX 1003.1-2001.
execve(2),
setrlimit(2),
sigaction(2),
siglongjmp(3),
sigsetjmp(3),
signal(7)
