Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

Michal Marek
2016-12-01T16:12:45Z

On 2016-12-01 04:39, Nicholas Piggin wrote:
> On Thu, 01 Dec 2016 02:35:54 +0000
> Ben Hutchings <ben@decadent.org.uk> wrote:
>> As I understand it, genksyms incorporates the definitions of a
>> function's parameter and return types - not just their names - and all
>> the types they refer to, recursively. So a structure size change
>> should change the version of all functions where the function and its
>> caller pass that structure between them, however indirectly. It finds
>> such indirect ABI breakage for me fairly regularly, though of course I
>> don't know that it finds everything.
>
> It is only the type name.
>
> Not only that but even if you did extend it further to structure type
> arrangement then you still have to deal with other structures followed
> via pointers. Or (rarer but not unheard of):
>
> - changes to structures without changes of the types of their members
> - changes to arguments without changes of their type

This is already covered by genksyms. Try make V=1 with
CONFIG_MODVERSIONS=y and add the -D option to one of the genksyms
command. I wanted to paste the expanded signature for
register_filesystem() as an example, but vger would probably drop the
mail for being too big :).

> - changes to semantics of functions
> - data structures derived in ways other than exported symbols, e.g.,
> fixed register for `current` on some archs

Right, this is something that genksyms has no idea about.

Michal