Re-introduction of sigcontext.

struct sigcontext and ucontext_t/mcontext_t are defined in such
a way that both (ie struct sigcontext and ucontext_t) can be
passed on to sigreturn. The signal handler is still given a
ucontext_t for maximum flexibility.

For backward compatibility sigreturn restores the state for the
alternate signal stack from sigcontext.sc_onstack and not from
ucontext_t.uc_stack. A good way to determine which value the
application has set and thus which value to use, is still open
for discussion.

NOTE: This change should only affect those binaries that use
      sigcontext and/or ucontext_t. In the source tree itself
      this is only doscmd. Recompilation is required for those
      applications.

This commit also fixes a lot of style bugs without hopefully
adding new ones.

NOTE: struct sigaltstack.ss_size now has type size_t again. For
      some reason I changed that into unsigned int.

Parts submitted by: bde
sigaltstack bug found by: bde

1 files changed, 16 insertions, 7 deletions

diff --git a/sys/sys/ucontext.h b/sys/sys/ucontext.h
index fda8bcd..b28c685 100644
--- a/sys/sys/ucontext.h
+++ b/sys/sys/ucontext.h
@@ -29,16 +29,25 @@
  */
 
 #ifndef _SYS_UCONTEXT_H_
-#define _SYS_UCONTEXT_H_ 1
+#define	_SYS_UCONTEXT_H_
 
 #include <machine/ucontext.h>
 
 typedef struct __ucontext {
-        struct __ucontext *uc_link;
-        stack_t         uc_stack;
-        sigset_t        uc_sigmask;
-        mcontext_t      uc_mcontext;
-        int             __spare__[8];
+	/*
+	 * Keep the order of the first three fields. Also,
+	 * keep them the first to fields in the structure.
+	 * This way we can have a union with struct
+	 * sigcontext and ucontext_t. This allows us to
+	 * support them both at the same time.
+	 * note: the union is not defined, though.
+	 */
+	sigset_t	uc_sigmask;
+	stack_t		uc_stack;
+	mcontext_t	uc_mcontext;
+
+	struct __ucontext_t *uc_link;
+	int		__spare__[8];
 } ucontext_t;
 
-#endif /* _SYS_UCONTEXT_H_ */
+#endif /* !_SYS_UCONTEXT_H_ */