BSP Developer's Guide

8
Writing Portable C Code
8.1.3 Static Data Alignment
Sometimes it is necessary to align a global static data element or structure on a
specific boundary type. This typically happens with CPU-specific data structures
that need cache boundary alignment.
To handle this situation, another toolchain-specific macro has been introduced.
The macro _WRS_DATA_ALIGN_BYTES(bytes) aligns the following data element
with the byte alignment specified.
For example:
_WRS_DATA_ALIGN_BYTES(16) int myData = 0xFE00235F;
This alignment macro should only be used with global data that has been
initialized. Uninitialized data may not be placed in the data section, and the macro
may not have the desired effect. Uninitialized data can be handled at runtime
using memalign( ) or other suitable functions.
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8.1.4 Runtime Alignment Checking
Checking the Alignment of a Data Item
You may need to know the alignment of a particular data item at runtime. Most
compilers provide an extension for accessing this information, but there is no
recognized standard for it. In the case of Wind River source code, the macro
_WRS_ALIGNOF(x) is used to return the alignment of an item in byte units.
if (WRS_ALIGNOF(itemA) < 4)
{
printf (“Error: itemA is not longword aligned”);
}
Verifying Pointer Alignment
Pointers can be deliberately cast to be a pointer to a different type of object with
different alignment requirements. Strict type checking at compile time is beneficial,
but there are situations in which this checking must be performed at runtime. For
this purpose, the macro _WRS_ALIGN_CHECK(ptr, type) is provided. This macro
evaluates to either TRUE or FALSE. TRUE is returned if the pointer ptr is aligned
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