Re: [PATCH] Verify __builtin_unreachable and __builtin_trap are not called with arguments

[Martin Jambor <mjambor at suse dot cz>]

Hi,

On Fri, Apr 22, 2016 at 09:24:31PM +0200, Richard Biener wrote:
> On April 22, 2016 7:04:31 PM GMT+02:00, Martin Jambor <mjambor@suse.cz> wrote:
> >Hi,
> >
> >this patch adds verification that __builtin_unreachable and
> >__builtin_trap are not called with arguments.  The problem with calls
> >to them with arguments is that functions like gimple_call_builtin_p
> >return false on them, because they return true only when
> >gimple_builtin_call_types_compatible_p does.  One manifestation of
> >that was PR 61591 where undefined behavior sanitizer did not replace
> >such calls with its thing as it should, but there might be others.
> >
> >I have included __builtin_trap in the verification because they often
> >seem to be handled together but can either remove it or add more
> >builtins if people think it better.  I concede it is a bit arbitrary.
> >
> >Honza said he has seen __builtin_unreachable calls with parameters in
> >LTO builds of Firefox, so it seems this might actually trigger, but I
> >also think we do not want such calls in the IL.
> >
> >I have bootstrapped and tested this on x86_64-linux (with all
> >languages and Ada) and have also run a C, C++ and Fortran LTO
> >bootstrap with the patch on the same architecture.  OK for trunk?
> 
> Shouldn't we simply error in the FEs for this given the builtins
> essentially have a prototype?  That is, error for non-matching args
> for the __built-in_ variant of _all_ builtins (treat them as
> prototyped)?
> 

We do that.  It is just that at times we produce a call to
__builtin_unreachable internally.  The only instance I know of is IPA
figuring out a call cannot happen in a legal program (for example
because it would lead to a call of abstract virtual functions) but
perhaps there are other places where we do it.

I thought we have fixed the issue of IPA leaving behind arguments in
the calls to __builtin_unreachable it produced and this verification
would simply made sure the bug does not come back but Honza's
observation suggests that it still sometimes happens.

Martin

> Richard.
> 
> >Thanks,
> >
> >Martin
> >
> >
> >2016-04-20  Martin Jambor  <mjambor@suse.cz>
> >
> >	* tree-cfg.c (verify_gimple_call): Check that calls to
> >	__builtin_unreachable or __builtin_trap do not have actual arguments.
> >---
> > gcc/tree-cfg.c | 20 ++++++++++++++++++++
> > 1 file changed, 20 insertions(+)
> >
> >diff --git a/gcc/tree-cfg.c b/gcc/tree-cfg.c
> >index 04e46fd..3385164 100644
> >--- a/gcc/tree-cfg.c
> >+++ b/gcc/tree-cfg.c
> >@@ -3414,6 +3414,26 @@ verify_gimple_call (gcall *stmt)
> >       return true;
> >     }
> > 
> >+  if (fndecl && DECL_BUILT_IN_CLASS (fndecl) == BUILT_IN_NORMAL)
> >+    {
> >+      switch (DECL_FUNCTION_CODE (fndecl))
> >+	{
> >+	case BUILT_IN_UNREACHABLE:
> >+	case BUILT_IN_TRAP:
> >+	  if (gimple_call_num_args (stmt) > 0)
> >+	    {
> >+	      /* Built-in unreachable with parameters might not be caught by
> >+		 undefined behavior santizer. */
> >+	      error ("__builtin_unreachable or __builtin_trap call with "
> >+		     "arguments");
> >+	      return true;
> >+	    }
> >+	  break;
> >+	default:
> >+	  break;
> >+	}
> >+    }
> >+
> >   /* ???  The C frontend passes unpromoted arguments in case it
> >      didn't see a function declaration before the call.  So for now
> >      leave the call arguments mostly unverified.  Once we gimplify
> 
>