svn commit: r341094 - head/sys/kern

[Konstantin Belousov]

Author: kib
Date: Tue Nov 27 19:50:58 2018
New Revision: 341094
URL: https://svnweb.freebsd.org/changeset/base/341094

Log:
  Improve sigonstack().
  
  Avoid relying on unsigned overflow for the test.
  Simplify expressions to avoid duplicate check for the range.
  Style.
  Add herald comment.
  
  Reviewed by:	jhb
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week
  Differential revision:	https://reviews.freebsd.org/D18361

Modified:
  head/sys/kern/kern_sig.c

Modified: head/sys/kern/kern_sig.c
==============================================================================
--- head/sys/kern/kern_sig.c	Tue Nov 27 19:45:25 2018	(r341093)
+++ head/sys/kern/kern_sig.c	Tue Nov 27 19:50:58 2018	(r341094)
@@ -615,20 +615,25 @@ signotify(struct thread *td)
 	}
 }
 
+/*
+ * Returns 1 (true) if altstack is configured for the thread, and the
+ * passed stack bottom address falls into the altstack range.  Handles
+ * the 43 compat special case where the alt stack size is zero.
+ */
 int
 sigonstack(size_t sp)
 {
-	struct thread *td = curthread;
+	struct thread *td;
 
-	return ((td->td_pflags & TDP_ALTSTACK) ?
+	td = curthread;
+	if ((td->td_pflags & TDP_ALTSTACK) == 0)
+		return (0);
 #if defined(COMPAT_43)
-	    ((td->td_sigstk.ss_size == 0) ?
-		(td->td_sigstk.ss_flags & SS_ONSTACK) :
-		((sp - (size_t)td->td_sigstk.ss_sp) < td->td_sigstk.ss_size))
-#else
-	    ((sp - (size_t)td->td_sigstk.ss_sp) < td->td_sigstk.ss_size)
+	if (td->td_sigstk.ss_size == 0)
+		return ((td->td_sigstk.ss_flags & SS_ONSTACK) != 0);
 #endif
-	    : 0);
+	return (sp >= (size_t)td->td_sigstk.ss_sp &&
+	    sp < td->td_sigstk.ss_size + (size_t)td->td_sigstk.ss_sp);
 }
 
 static __inline int