Boaz Harrosh wrote: > I would at least expect a big fat comment explaining what happened to the > structure on what known ARCHs, and how it is expected to look in memory. > And a BUILD_BUG_ON to make sure of that. You may have a point. Struct layout on some architectures changes between compiler default ABIs in these implicit-padding cases. Kernel binary compatibility will be affected. It is a good reason why we have explicit padding to natural alignment normally. >From http://wiki.debian.org/ArmEabiPort "With the new ABI, default structure packing changes, as do some default data sizes and alignment (which also have a knock-on effect on structure packing). In particular the minimum size and alignment of a structure was 4 bytes. Under the EABI there is no minimum and the alignment is determined by the types of the components it contains. This will break programs that know too much about the way structures are packed and can break code that writes binary files by dumping and reading structures." "One of the key differences between the traditional GNU/Linux ABI and the EABI is that 64-bit types (like long long) are aligned differently. In the traditional ABI, these types had 4-byte alignment; in the EABI they have 8-byte alignment. As a result, if you use the same structure definitions (in a header file) and include it in code used in both the kernel and in application code, you may find that the structure size and alignment differ." -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
