1 files changed, 94 insertions, 0 deletions
diff --git a/libc/syscall/signal.c b/libc/syscall/signal.c
new file mode 100644
index 0000000..dbeac4a
--- /dev/null
+++ b/libc/syscall/signal.c
@@ -0,0 +1,94 @@
+
+#ifndef __MSDOS__
+#ifdef __AS386_16__
+
+#include <errno.h>
+#include <signal.h>
+
+typedef __sighandler_t Sig;
+
+extern int __signal __P((int, __sighandler_t));
+static Sig system_signal();
+
+Sig __sigtable[_NSIG-1];
+
+/*
+ * Signal handler.
+ *
+ */
+
+/*
+ * KERNEL INTERFACE:
+ *   It is assumed the kernel will never give us a signal we haven't
+ *   _explicitly_ asked for!
+ *
+ * The Kernel need only save space for _one_ function pointer
+ * (to system_signal) and must deal with SIG_DFL and SIG_IGN
+ * in kernel space.
+ *
+ * When a signal is required the kernel must set all the registers as if
+ * returning from a interrupt normally then push the number of the signal
+ * to be generated, push the current pc value, then set the pc to the
+ * address of the 'system_signal' function.
+ */
+
+Sig
+signal(number, pointer)
+int number;
+Sig pointer;
+{
+   Sig old_sig;
+   int rv;
+   if( number < 1 || number >= _NSIG ) { errno=EINVAL; return SIG_ERR; }
+
+   if( pointer == SIG_DFL || pointer == SIG_IGN )
+      rv = __signal(number, pointer);
+   else
+      rv = __signal(number, (__sighandler_t) system_signal);
+
+   if( rv < 0 ) return SIG_ERR;
+
+   old_sig = __sigtable[number-1];
+   __sigtable[number-1] = pointer;
+
+   return old_sig;
+}
+
+#asm
+  .text
+_system_signal:		! When this is called by the kernel the stack contains
+  pushf			! in order:
+  push	ax		! 
+  push	bx		!    The signal number,			(NOS)
+  push	cx		!    The program counter,		(TOS)
+  push	dx		!
+  push	si		! It does NOT contain the CS register or the flags.
+  push	di		! This means it cannot be unraveled by an iret.
+  push	bp
+  push	es		! Note also only ES segment register is saved.
+  mov	bx,sp		! Unlike minix the rv from a system call is in AX.
+  mov	bx,[bx+20]
+#if __FIRST_ARG_IN_AX__
+  mov	ax,bx
+#else
+  push	bx		! NB this is _unchecked_, do we want to ?
+#endif
+  add	bx,bx
+  mov	bx,[bx+___sigtable-2]	! Offset by 2 cause no entry for signal 0
+  call	bx		! Do we want to check BX for 0 or 1 ?
+  inc	sp
+  inc	sp
+  pop	es
+  pop	bp
+  pop	di
+  pop	si
+  pop	dx
+  pop	cx
+  pop	bx
+  pop	ax
+  popf
+  ret	#2		! Get rid of the signum too.
+#endasm
+
+#endif /* __AS386_16__ */
+#endif /* __MSDOS__ */