Re: [PATCH i-g-t] tests/gem_softpin: Fix compiler warning on 32bit systems

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On 10/12/15 16:43, Tvrtko Ursulin wrote:

Hi,

On 10/12/15 14:58, Mika Kuoppala wrote:
We get build error as we try to cast from ptr to integer
of different size on 32 bit platforms. Use unsigned long
as the cast, it will work with both 32 and 64 bit
systems.

Cc: Vinay Belgaumkar <vinay.belgaumkar@xxxxxxxxx>
Signed-off-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxx>
---
  tests/gem_softpin.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tests/gem_softpin.c b/tests/gem_softpin.c
index 7bee16b..0919716 100644
--- a/tests/gem_softpin.c
+++ b/tests/gem_softpin.c
@@ -155,7 +155,7 @@ static uint32_t init_userptr(int fd,
i915_gem_userptr *userptr, void *ptr,

      memset((void*)userptr, 0, sizeof(i915_gem_userptr));

-    userptr->user_ptr = (uint64_t)ptr; /* Need the cast to overcome
compiler warning */
+    userptr->user_ptr = (unsigned long)ptr; /* Need the cast to
overcome compiler warning */
      userptr->user_size = size;
      userptr->flags = 0; /* use synchronized operation */

@@ -270,7 +270,7 @@ static void setup_execbuffer(struct
drm_i915_gem_execbuffer2 *execbuf,
                   struct drm_i915_gem_exec_object2 *exec_object,
                   int ring, int buffer_count, int batch_length)
  {
-    execbuf->buffers_ptr = (uint64_t)exec_object;
+    execbuf->buffers_ptr = (unsigned long)exec_object;
      execbuf->buffer_count = buffer_count;
      execbuf->batch_start_offset = 0;
      execbuf->batch_len = batch_length;
@@ -417,7 +417,7 @@ static void gem_pin_bo_test(void)
                 EXEC_OBJECT_PINNED, pinning_offset);
      setup_exec_obj(&exec_object2[1], batch_buf_handle, 0, 0);
      exec_object2[1].relocation_count = 1;
-    exec_object2[1].relocs_ptr = (uint64_t)reloc;
+    exec_object2[1].relocs_ptr = (unsigned long)reloc;

      ring = I915_EXEC_RENDER;

I had to try it to believe it and indeed gcc complains with "warning:
cast from pointer to integer of different size [-Wpointer-to-int-cast]",
which I don't really understand since cast is to a wider or equally wide
data type.

I think the warning is really there for the pointer-to-signed-int conversion, in case that does an unexpected sign extension -- yes, I have seen machines where pointers were considered signed :( I suppose the result of converting a signed-pointer to unsigned-long-long might be "surprising" ...

Or maybe the gcc writers just thought it was more general to check for dest_size != source_size rather than < :-?

Vinay had uintptr_t there originally which does not suffer from this
warning so this one is my fault. I don't get the gcc logic but whatever.

'uintptr_t' should be the right type for the cast; and you should then be able assign that to any larger unsigned type without getting compiler warnings!

[Aside: I've also seen at one machine where there simply wasn't any type that could be used for uintptr_t; it had 4-byte 'long's and no 'long long', but pointers were 6 bytes!]

.Dave.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Regards,

Tvrtko
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