libgo patch committed: Don't clobber context when catching signal

[Ian Lance Taylor]

This patch to libgo fixes a dumb bug in which catching a signal via the
os/signal package could clobber the saved split-stack context, leading
to disaster if the signal arrived at the wrong time.  Bootstrapped and
ran Go testsuite on x86_64-unknown-linux-gnu.  Committed to mainline.
Will commit to 4.8 branch when it reopens.

Ian


diff -r 9c8c4538fce7 libgo/runtime/go-signal.c
--- a/libgo/runtime/go-signal.c	Sat Oct 12 21:13:58 2013 -0700
+++ b/libgo/runtime/go-signal.c	Mon Oct 14 14:00:36 2013 -0700
@@ -399,6 +399,7 @@
 {
   G *gp;
   M *mp;
+  void *stack_context[10];
 
   /* We are now running on the stack registered via sigaltstack.
      (Actually there is a small span of time between runtime_siginit
@@ -409,7 +410,7 @@
   if (gp != NULL)
     {
 #ifdef USING_SPLIT_STACK
-      __splitstack_getcontext (&gp->stack_context[0]);
+      __splitstack_getcontext (&stack_context[0]);
 #endif
     }
 
@@ -432,7 +433,7 @@
   if (gp != NULL)
     {
 #ifdef USING_SPLIT_STACK
-      __splitstack_setcontext (&gp->stack_context[0]);
+      __splitstack_setcontext (&stack_context[0]);
 #endif
     }
 }