[Mesa-dev] FPE Invalid Operation

[Ilia Mirkin]

On Mon, Sep 5, 2016 at 12:55 PM, Bram Stolk <b.stolk at gmail.com> wrote:
> Hey,
>
> Do you guys test with Floating-Point-Exceptions enabled?

I think most people just test with whatever is the default.

> Because on Intel-Haswell, I can trigger a FPE with a simple glClearColor and
> glClear.
> I think glClear is doing bad FP math on Haswell.
>
> https://software.intel.com/en-us/forums/graphics-driver-bug-reporting/topic/681580

Unfortunately you don't have any debug info for your mesa build.

>
> I recommend doing a:
>
> feenableexcept( FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW );
>
> In your test-suite.

I did that but was unable to trigger the error on a i7-920 CPU and an
NVIDIA GPU (driven by nouveau) in some simple tests. Perhaps a change
in how HSW reports errors, or could be a HSW- (or gen7+) specific code
path.

If you're able to, make a local build, adding -O0 to cflags, and don't
strip the debug info. That should show you exactly where the issue
lies.

Separately, if you can make a small program that reproduces the issue
for you (e.g. with glut + epoxy), that would help others test and
figure out what's going on.

  -ilia

P.S. for reference, this is the (whitespace-damaged) patch I applied
to piglit for my testing:

diff --git a/tests/util/piglit-framework-gl.h b/tests/util/piglit-framework-gl.h
index 81c1a5e..1510fc1 100644
--- a/tests/util/piglit-framework-gl.h
+++ b/tests/util/piglit-framework-gl.h
@@ -235,6 +235,7 @@ void
 piglit_gl_test_run(int argc, char *argv[],
                   const struct piglit_gl_test_config *config);

+#include <fenv.h>
 #ifdef __cplusplus
 #  define PIGLIT_EXTERN_C_BEGIN extern "C" {
 #  define PIGLIT_EXTERN_C_END   }
@@ -263,6 +264,7 @@ piglit_gl_test_run(int argc, char *argv[],
                 piglit_disable_error_message_boxes();                        \
                                                                              \
                 piglit_gl_test_config_init(&config);                         \
+               feenableexcept( FE_DIVBYZERO | FE_INVALID | FE_OVERFLOW );   \
                                                                              \
                 config.init = piglit_init;                                   \
                 config.display = piglit_display;                             \