sigaction seems to return new action as old action

Created by: egrimley

This seems to happen on all architectures. Test program:

#include <signal.h>
#include <stdio.h>
#include <string.h>

int main()
{
    struct sigaction act, oldact;
    memset(&act, 0, sizeof(act));
    memset(&oldact, 0, sizeof(act));

    act.sa_handler = (void *)0x1001;
    sigaction(28, &act, &oldact);
    printf("%p\n", oldact.sa_handler);

    act.sa_handler = (void *)0x1002;
    sigaction(28, &act, &oldact);
    printf("%p\n", oldact.sa_handler);

    act.sa_handler = (void *)0x1003;
    sigaction(28, &act, &oldact);
    printf("%p\n", oldact.sa_handler);

    return 0;
}

Output running natively:

(nil)
0x1001
0x1002

Output running under DynamoRIO:

0x1001
0x1002
0x1003