diff mbox series

[PR51447] restore the global reg var before returning from main

Message ID orbllx4qll.fsf@livre.home
State New
Headers show
Series [PR51447] restore the global reg var before returning from main | expand

Commit Message

Alexandre Oliva June 5, 2020, 12:57 p.m. UTC 
The testcase for PR51447, on x86_64, uses rbx as a global register
variable for the global PTR variable.

A runtime system might legitimately hold in rbx a value expected to be
preserved across the call to main, but its use as a global register
variable stops main from preserving it.

We've observed failures of this test on x86_64-wrs-vxworks7r2, because
of this problem, and this patch fixes them.  I've also tested it on
x86_64-linux-gnu, -m64 and -m32.  Ok to install?

Since main is not supposed to be callable, I suppose we might instead
prevent global register variables from affecting the registers saved or
restored by main, but I don't have a patch for that.  I could give it a
shot, if there's consensus that that would be a better fix.


for  gcc/testsuite/ChangeLog

	PR rtl-optimization/51447
	* gcc.c-torture/execute/pr51447.c (main): Preserve call-saved
	register.
---
 gcc/testsuite/gcc.c-torture/execute/pr51447.c |    6 ++++++
 1 file changed, 6 insertions(+)

Comments

Li, Pan2 via Gcc-patches June 9, 2020, 7:42 p.m. UTC | #1 
On Fri, 2020-06-05 at 09:57 -0300, Alexandre Oliva wrote:
> The testcase for PR51447, on x86_64, uses rbx as a global register
> variable for the global PTR variable.
> 
> A runtime system might legitimately hold in rbx a value expected to be
> preserved across the call to main, but its use as a global register
> variable stops main from preserving it.
> 
> We've observed failures of this test on x86_64-wrs-vxworks7r2, because
> of this problem, and this patch fixes them.  I've also tested it on
> x86_64-linux-gnu, -m64 and -m32.  Ok to install?
> 
> Since main is not supposed to be callable, I suppose we might instead
> prevent global register variables from affecting the registers saved or
> restored by main, but I don't have a patch for that.  I could give it a
> shot, if there's consensus that that would be a better fix.
I'm not sure special casing this is necessarily worth the effort.

> 
> 
> for  gcc/testsuite/ChangeLog
> 
> 	PR rtl-optimization/51447
> 	* gcc.c-torture/execute/pr51447.c (main): Preserve call-saved
> 	register.
OK
jeff
>
diff mbox series

Patch

diff --git a/gcc/testsuite/gcc.c-torture/execute/pr51447.c b/gcc/testsuite/gcc.c-torture/execute/pr51447.c
index 887ddb7..1d00953 100644
--- a/gcc/testsuite/gcc.c-torture/execute/pr51447.c
+++ b/gcc/testsuite/gcc.c-torture/execute/pr51447.c
@@ -14,6 +14,9 @@  int
 main (void)
 {
   __label__ nonlocal_lab;
+#ifdef __x86_64__
+  void *save = ptr;
+#endif
   __attribute__((noinline, noclone)) void
     bar (void *func)
       {
@@ -25,5 +28,8 @@  main (void)
 nonlocal_lab:
   if (ptr != &&nonlocal_lab)
     abort ();
+#ifdef __x86_64__
+  ptr = save; /* Restore the call-saved register.  */
+#endif
   return 0;
 }