Re: alignment and packed structs

[RVP <rvp%SDF.ORG@localhost>]

On Wed, 6 Jan 2021, Patrick Welche wrote:

> I just tried to compile if_iwn as a module. It failed with
>
> dev/pci/if_iwn.c:2685:6: error: converting a packed 'struct iwn_fw_dump' pointer (alignment 1) to a 'uint32_t' {aka 'unsigned int'} pointer (alignment 4) may result in an unaligned pointer value [-Werror=address-of-packed-member]
>
>
> I got around it with
> ...
> Why isn't this necessary when building if_iwn.c as part of a kernel?

This isn't an isolated case. I recently built some other (Intel
DRM) code as modules and had to "fix " the code in 3 or 4 places
for the whole kernel/module compilation to complete successfully.
I figured it was a case of slightly different compiler flags being
used for the monolithic vs. modular kernel builds.

-RVP