* lab/interupts program is added to experiment with sigaction and

sigaltstack.

added:
  lab/interrupts/
  lab/interrupts/Makefile
  lab/interrupts/inf_loop.s
  lab/interrupts/main
  lab/interrupts/main.c

TODO

@@ -2,6 +2,7 @@
 CHECK  - Implement guardians. 
 CHECK  - clean up after file ports are dead by flushing/closing the
          underlying file handle.
+  - Flush and close output-port on exit.
 
 * Interrupts:
   - pcb should have an engine-counter field that's decremented on

lab/interrupts/Makefile

@@ -0,0 +1,6 @@
+
+all:	main
+
+main:	inf_loop.s main.c
+	gcc -o main inf_loop.s main.c
+

lab/interrupts/inf_loop.s

@@ -0,0 +1,8 @@
+
+.globl _inf_loop
+
+_inf_loop:
+  movl %esp, %eax
+  movl $0, %esp
+L_loop:
+  jmp L_loop

lab/interrupts/main.c

@@ -0,0 +1,90 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <signal.h>
+
+extern void inf_loop();
+void register_handlers();
+void register_alt_stack();
+
+int main(int argc, char** argv){
+  fprintf(stderr, "Entering ... \n");
+  register_handlers();
+  register_alt_stack();
+  inf_loop();
+  fprintf(stderr, "Done\n");
+  return 0;
+}
+
+#if 0
+     #include <signal.h>
+
+     struct  sigaction {
+             union {
+                     void    (*__sa_handler)(int);
+                     void    (*__sa_sigaction)(int, struct __siginfo *, void *);
+             } __sigaction_u;                /* signal handler */
+             int     sa_flags;               /* see signal options below */
+             sigset_t sa_mask;               /* signal mask to apply */
+     };
+
+     #define sa_handler      __sigaction_u.__sa_handler
+     #define sa_sigaction    __sigaction_u.__sa_sigaction
+
+     int
+     sigaction(int sig, const struct sigaction * restrict act,
+         struct sigaction * restrict oact);
+#endif
+
+void handler(int signo, struct __siginfo* info, ucontext_t* uap){
+  fprintf(stderr, "Handler Called!\n");
+}
+
+void
+register_handlers(){
+  struct sigaction sa;
+  sa.sa_sigaction = (void(*)(int,struct __siginfo*,void*)) handler;
+  sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
+  sa.sa_mask = 0;
+  int err = sigaction(SIGINT, &sa, 0);
+  if(err){
+    fprintf(stderr, "Sigaction Failed: %s\n", strerror(errno));
+    exit(-1);
+  }
+}
+
+
+#if 0
+SYNOPSIS
+     #include <sys/types.h>
+     #include <signal.h>
+
+     struct sigaltstack {
+             char   *ss_sp;
+             int     ss_size;
+             int     ss_flags;
+     };
+
+     int
+     sigaltstack(const struct sigaltstack *ss, struct sigaltstack *oss);
+#endif
+
+void
+register_alt_stack(){
+  char* stk = malloc(SIGSTKSZ);
+  if(stk == 0){
+    fprintf(stderr, "Cannot maloc an alt stack\n");
+    exit(-1);
+  }
+
+  struct sigaltstack sa;
+  sa.ss_sp = stk;
+  sa.ss_size = SIGSTKSZ;
+  sa.ss_flags = 0;
+  int err = sigaltstack(&sa, 0);
+  if(err){
+    fprintf(stderr, "Cannot set alt stack: %s\n", strerror(errno));
+    exit(-1);
+  }
+  fprintf(stderr, "alt-stack of size %d set\n", SIGSTKSZ);
+}