mem_host_flags: check returned pointer for NULL (#1924)

The specification states that `clEnqueueMapImage` and
`clEnqueueMapBuffer` should return NULL on error. Ensure this is
checked.

This testing gap was caught by a compiler warning about `dataPtr` being
written but not read. With this fix, there are no more
Wunused-but-set-variable warnings in this test, so reenable the warning.

Signed-off-by: Sven van Haastregt <sven.vanhaastregt@arm.com>

test_conformance/mem_host_flags/CMakeLists.txt

@@ -6,6 +6,4 @@ set(${MODULE_NAME}_SOURCES
     mem_host_image.cpp
 )
 
-set_gnulike_module_compile_flags("-Wno-unused-but-set-variable")
-
 include(../CMakeCommon.txt)

test_conformance/mem_host_flags/checker_image_mem_host_no_access.hpp

@@ -135,6 +135,14 @@ cl_int cImage_check_mem_host_no_access<T>::verify_RW_Image_Mapping()
         err = FAILURE;
         return err;
     }
+    else if (dataPtr != nullptr)
+    {
+        log_error("Calling clEnqueueMapImage (CL_MAP_WRITE) on a memory object "
+                  "created with the CL_MEM_HOST_NO_ACCESS flag should fail "
+                  "and return NULL\n");
+        err = FAILURE;
+        return err;
+    }
     else
     {
         log_info("Test succeeded\n\n");
@@ -154,6 +162,14 @@ cl_int cImage_check_mem_host_no_access<T>::verify_RW_Image_Mapping()
         err = FAILURE;
         return err;
     }
+    else if (dataPtr != nullptr)
+    {
+        log_error("Calling clEnqueueMapImage (CL_MAP_READ) on a memory object "
+                  "created with the CL_MEM_HOST_NO_ACCESS flag should fail "
+                  "and return NULL\n");
+        err = FAILURE;
+        return err;
+    }
     else
     {
         log_info("Test succeeded\n\n");

test_conformance/mem_host_flags/checker_mem_host_no_access.hpp

@@ -190,6 +190,14 @@ cl_int cBuffer_check_mem_host_no_access<T>::verify_RW_Buffer_mapping()
         err = FAILURE;
         return FAILURE;
     }
+    else if (dataPtr != nullptr)
+    {
+        log_error("Calling clEnqueueMapBuffer (CL_MAP_READ) on a memory object "
+                  "created with the CL_MEM_HOST_NO_ACCESS flag should fail "
+                  "and return NULL\n");
+        err = FAILURE;
+        return err;
+    }
     else
     {
         log_info("Test succeeded\n\n");
@@ -207,6 +215,15 @@ cl_int cBuffer_check_mem_host_no_access<T>::verify_RW_Buffer_mapping()
         err = FAILURE;
         return FAILURE;
     }
+    else if (dataPtr != nullptr)
+    {
+        log_error(
+            "Calling clEnqueueMapBuffer (CL_MAP_WRITE) on a memory object "
+            "created with the CL_MEM_HOST_NO_ACCESS flag should fail "
+            "and return NULL\n");
+        err = FAILURE;
+        return err;
+    }
     else
     {
         log_info("Test succeeded\n\n");