Re: [PATCH v2 02/10] export: explicitly align struct kernel_symbol

[Greg KH]

On Tue, Aug 13, 2019 at 01:16:59PM +0100, Matthias Maennich wrote:
> This change allows growing struct kernel_symbol without wasting bytes to
> alignment. It also concretized the alignment of ksymtab entries if
> relative references are used for ksymtab entries.
> 
> struct kernel_symbol was already implicitly being aligned to the word
> size, except on x86_64 and m68k, where it is aligned to 16 and 2 bytes,
> respectively.
> 
> As far as I can tell there is no requirement for aligning struct
> kernel_symbol to 16 bytes on x86_64, but gcc aligns structs to their
> size, and the linker aligns the custom __ksymtab sections to the largest
> data type contained within, so setting KSYM_ALIGN to 16 was necessary to
> stay consistent with the code generated for non-ASM EXPORT_SYMBOL(). Now
> that non-ASM EXPORT_SYMBOL() explicitly aligns to word size (8),
> KSYM_ALIGN is no longer necessary.
> 
> In case of relative references, the alignment has been changed
> accordingly to not waste space when adding new struct members.
> 
> As for m68k, struct kernel_symbol is aligned to 2 bytes even though the
> structure itself is 8 bytes; using a 4-byte alignment shouldn't hurt.
> 
> I manually verified the output of the __ksymtab sections didn't change
> on x86, x86_64, arm, arm64 and m68k. As expected, the section contents
> didn't change, and the ELF section alignment only changed on x86_64 and
> m68k. Feedback from other archs more than welcome.
> 
> Co-developed-by: Martijn Coenen <maco@xxxxxxxxxxx>
> Signed-off-by: Martijn Coenen <maco@xxxxxxxxxxx>
> Signed-off-by: Matthias Maennich <maennich@xxxxxxxxxx>

Ick, messy, nice fix.

Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>