PR10274 Fix exelib -O3 testcase.

The testcase now uses noinline, an empty asm statement and a volatile
variable to prevent the function getting inlined, being totally unrolled
or the recursive call being replaced with an inner-iteration.

This does defeat part of the testcase though, which was testing unwinding
through an optimized recursive function. But it seems the best we can do.

* testsuite/systemtap.exelib/exelib.exp: Add -O3 to the mix.
* testsuite/systemtap.exelib/uprobes_exe.c: Use volatile bar and mark
  main_func noinline.
* testsuite/systemtap.exelib/uprobes_lib.c: Use volatile foo and mark
  lib_func noinline.

1 files changed, 13 insertions, 4 deletions

diff --git a/testsuite/systemtap.exelib/uprobes_exe.c b/testsuite/systemtap.exelib/uprobes_exe.c
index b4811335..d2905637 100644
--- a/testsuite/systemtap.exelib/uprobes_exe.c
+++ b/testsuite/systemtap.exelib/uprobes_exe.c
@@ -12,18 +12,27 @@
 // function from our library
 int lib_main (void);
 
-void
+// volatile static variable to prevent folding of main_func
+static volatile int bar;
+
+// Marked noinline and has an empty asm statement to prevent inlining
+// or optimizing away totally.
+int
+__attribute__((noinline))
 main_func (int foo)
 {
-  if (foo > 1)
-    main_func (foo - 1);
+  asm ("");
+  if (foo - bar > 0)
+    bar = main_func (foo - bar);
   else
     lib_main();
+  return bar;
 }
 
 int
 main (int argc, char *argv[], char *envp[])
 {
-  main_func (3);
+  bar = 1;
+  bar = main_func (3);
   return 0;
 }