// Test source and desired /real output:
#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
void handler(int sig)
{
unsigned int a;
// to prevent uninitialized stack, normally a = 0
if ( a>10 ) a = 0;
a = a + 1;
printf ("new value: %d\n" , a );
if (a > 7) _exit(a);
return;
}
int main()
{
int ret;
char * stackA = malloc(SIGSTKSZ);
char * stackB = malloc(SIGSTKSZ);
stack_t ssA = {
.ss_size = SIGSTKSZ,
.ss_sp = stackA,
};
stack_t ssB = {
.ss_size = SIGSTKSZ,
.ss_sp = stackB,
};
struct sigaction sa = {
.sa_handler = handler,
.sa_flags = SA_ONSTACK
};
// no error checking, only debug output
ret = sigfillset(&sa.sa_mask);
printf ( "Sigfillset: %d\n" , ret );
ret = sigaction(SIGUSR1, &sa, 0);
printf ( "Sigaction: %d\n" , ret );
while (1) {
printf ("On stack A -- " );
ret = sigaltstack(&ssA, 0);
printf ( "sigaltstack return: %d -- " , ret );
kill(0, SIGUSR1);
sleep(1);
printf (" -- " );
kill(0, SIGUSR1);
sleep(1);
printf ("On stack B -- " );
ret = sigaltstack(&ssB, 0);
printf ( "sigaltstack return: %d -- " , ret );
kill(0, SIGUSR1);
sleep(1);
}
}
/* Desired output:
Sigfillset: 0
Sigaction: 0
On stack A -- sigaltstack return: 0 -- new value: 1
-- new value: 2
On stack B -- sigaltstack return: 0 -- new value: 1
On stack A -- sigaltstack return: 0 -- new value: 3
-- new value: 4
On stack B -- sigaltstack return: 0 -- new value: 2
On stack A -- sigaltstack return: 0 -- new value: 5
-- new value: 6
On stack B -- sigaltstack return: 0 -- new value: 3
On stack A -- sigaltstack return: 0 -- new value: 7
-- new value: 8
Output for ppc without patch:
Sigfillset: 0
Sigaction: 0
On stack A -- sigaltstack return: 0 -- new value: 1
-- new value: 2
On stack B -- sigaltstack return: 0 -- new value: 3 // WRONG!!
On stack A -- sigaltstack return: 0 -- new value: 4
-- new value: 5 // WRONG AGAIN!
...
*/
