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

[Ian Campbell]

On Fri, 2016-12-09 at 13:33 +1000, Nicholas Piggin wrote:
>Â
> Well I simply tested the outcome. If you have:
> 
> struct blah {
> Â int x;
> };
> int foo(struct blah *blah)
> {
> Â return blah->x;
> }
> EXPORT(foo);
> 
> $ nm vmlinux | grep __crc_foo
> 00000000a0cf13a0 A __crc_foo
> 
> Now change to
> 
> struct blah {
> Â int y;
> Â int x;
> };
> 
> $ nm vmlinux | grep __crc_foo
> 00000000a0cf13a0 A __crc_foo
> 
> It just doesn't catch these things.

I found the same when I just added your snippet to init/main.c.

_But_ when I moved the struct into include/types.h (which happened to
be included by init/main.c) then, with just x in the struct:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.oÂÂ| grep __crc_foo
    s#blah struct blah { int x ; }Â
    foo int foo ( s#blah * )Â
    000000000cd0312e A __crc_foo

but adding y:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.oÂÂ| grep __crc_foo
    s#blah struct blah { int x ; int y ; }Â
    foo int foo ( s#blah * )Â
    00000000eda220c6 A __crc_foo

So it does catch things in that case.

With struct blah inline in main.c it was:

    $ make -s init/main.{o,symtypes} && grep -E foo\|blah init/main.symtypes && nm init/main.oÂÂ| grep __crc_foo
    s#blah struct blah { UNKNOWN }Â
    foo int foo ( s#blah * )Â
    00000000a0cf13a0 A __crc_foo

So I suppose it only cares about structs which are in headers, which I
guess makes sense. I think it is working in at least one of the
important cases.

Ian.