To begin with I will point out the operating system here is RTEMS, it is an Open source RTOS and the source can be found here:
I have a pretty simple program that sets up a signal handler for SIGSEGV (which i believe is supported) using sigaction call from the documentation here:
http://docs.rtems.org/releases/rtemsdocs-4.9.2/share/rtems/html/posix_users/posix_users00033.html
My program essentially boils down to this:
void HandleAndPrintSignal()
{
printf("I am in the segfault signal handler AND I WILL HANDLE YOUR SIG!!!!\n");
exit(1);
}
void *POSIX_Init(void *args)
{
printf("BENS BIG NOTE: Initializing Signal Handler\n");
struct sigaction sa;
sa.sa_handler = HandleAndPrintSignal;
sigemptyset(&sa.sa_mask);
sa.sa_flags = SA_SIGINFO;
if (sigaction (SIGSEGV, &sa, 0)) {
printf("A ERROR OCCURED WITH THIS!");
exit(1);
}
int *p = NULL;
*(p--) = 5; // Causes segfault
}
However, the problem is that when i cause a segfault in my program, the signal handler is not called but instead a kernel process is called in vectors_init.c (RTEMS source) to print a stack trace. Is there something special that I need to do to get SIGSEGV signal in my rtems program?
So the explanation of this is that RTEMS does not handle signals the way that I thought it does.
There are some POSIX signals which are really exceptions at the hardware level. for eg. SIGSEGV, SIGBUS, and SIGFPE. The exact semantics of what is possible when this occurs is defined by POSIX but the magic starts with an architecture and BSP specific handler. Since the general rule is to avoid these faults in embedded systems, the default action is often something like a kernal stack trace, or other BSP specific code.
Some BSPs have support for installing an addition to the exception handler which will propagate the hardware fault into a software signal but this is primarily used to get SIGFPE in languages like Ada mapped to language specific exception handlers.
As a general rule, POSIX signals are rarely used in embedded systems, those that originate in hardware exceptions are designed out and considered unrecoverable faults, and the software only signals may be used.
As a summary: in order to get the desired behavior i need code that is installed which maps hardware exceptions -> POSIX signals.