Am 19.04.2016 um 21:30 schrieb Gilles Chanteperdrix:
On Tue, Apr 19, 2016 at 09:10:52PM +0200, Gilles Chanteperdrix wrote:
On Tue, Apr 19, 2016 at 12:21:48AM +0200, Johann Obermayr wrote:
Hello,
is there a way to handle a stack overflow with a xenomai rt_task ?
this example work for a standard linux
This example does not handle stack overflows. It handles the SIGSEGV
signal, which may happen in case of stack overflow or for many other
reasons. In order to handle properly a stack overflow, you would
have to:
- use the SA_SIGINFO flag and setup an sa_sigaction handler instead
of sa_handler with additional arguments
- in the handler, use the additional arguments to extract the fault
address and architecture specific stack pointer and check that the
fault address is "near" the stack pointer (and in fact it may not be
at all)
- or walk /proc/self/maps to find the mapping where the fault
address is and check if it is "near" a thread stack.
- or check that the fault program counter is an operation involving
a store or read relative to the stack pointer.
But I do not think there is a reliable way to detect stack
overflows. It is even possible to overflow the stack so much that
the code appears to work by writing to another thread stack (if the
overflow length is larger than the glibc guard size).
#define _XOPEN_SOURCE 700
#include <stdio.h>
#include <signal.h>
#include <unistd.h>
void handler(int sig)
{
printf("stack overflow: %d\n", sig);
_exit(1);
}
Also, using printf in a signal handler is bad. printf is not async
signal safe.
And on my platform at least, SIGSTKSZ is something like 8192 or
16384 which may be too small for a printf, so printf could cause a
stack overflow (depending on the length of the printed string).
Hello,
Thanks you for answer.
i have refactoring the example.
Here is the source
-------------------------------------------------- begin source
#define __USE_BSD
#include <stdio.h>
#include <malloc.h>
#include <memory.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/mman.h> //mloockall
#ifdef USE_XENOMAI
#include <native/task.h>
#endif
#define SIGSTACKSIZE 32*1024
void dohandler(const char *name, int sig, siginfo_t *info, void *ptr)
{
char buf[256];
int len = sprintf(buf, "%s: signal_handler: %d\n", name, sig);
write(STDOUT_FILENO, buf, len) ;
_exit(1);
}
void signal_handler_linux(int sig, siginfo_t *info, void *ptr)
{
dohandler("linux", sig, info, ptr);
}
void signal_handler_xeno(int sig, siginfo_t *info, void *ptr)
{
dohandler("xeno", sig, info, ptr);
}
unsigned infinite_recursion(unsigned x) {
char buf[4*128*1024];
memset(buf, 0, sizeof(buf));
return infinite_recursion(x)+1;
}
void help()
{
printf("program <options>\n");
printf(" --help this help\n");
printf(" --sigstack use the sigalstack function to set a
own signal stack\n");
_exit(1);
}
int main(int argc, char *argv[])
{
#ifdef USE_XENOMAI
RT_TASK mainTask;
int rval;
#endif
static char stack[SIGSTACKSIZE];
stack_t ss = {
.ss_size = SIGSTACKSIZE,
.ss_sp = stack,
.ss_flags = SS_ONSTACK,
};
struct sigaction sa = {
.sa_sigaction = signal_handler_linux,
.sa_flags = SA_SIGINFO,
};
int i;
int use_sigstack = 0;
mlockall(MCL_CURRENT|MCL_FUTURE);
for(i = 1; i < argc; i++) {
if (strcmp(argv[i], "--help") == 0) help();
if (strcmp(argv[i], "--sigstack") == 0) use_sigstack = 1;
}
if (use_sigstack) {
sa.sa_flags |= SA_ONSTACK;
sigaltstack(&ss, 0);
}
sigfillset(&sa.sa_mask);
sigaction(SIGSEGV, &sa, 0);
#ifdef USE_XENOMAI
rval = rt_task_shadow(&mainTask, "MainRecursion", 5, 0);
if (rval)
printf("rt_task_shadow return:%d\n", rval);
rval = rt_sigaction(SIGSEGV, signal_handler_xeno);
if (rval)
printf("rt_sigaction return:%d\n", rval);
#endif
infinite_recursion(0);
}
--------------------------------------------- end source
i create to example first without xenomai, second with xenomai.
root@sigmatek-arm-mp:~# ./signaltest01arm
Segmentation fault
root@sigmatek-arm-mp:~# ./signaltest01arm --sigstack
linux: signal_handler: 11
root@sigmatek-arm-mp:~# ./signaltest01armx
Segmentation fault
root@sigmatek-arm-mp:~# ./signaltest01armx --sigstack
Segmentation fault
root@sigmatek-arm-mp:~#
for a standard linux thread the function sigaltstack will work correct.
But not with xenomai (rt_task_shadow)
we use kernel 3.0.53 & xenomai 2.6.2.1.
regards
Johann
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