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

Ian Campbell
2016-12-09T15:47:37Z

On Fri, 2016-12-09 at 13:33 +1000, Nicholas Piggin wrote:
>
> Well I simply tested the outcome. If you have:
>
> struct blah {
>   int x;
> };
> int foo(struct blah *blah)
> {
>   return blah->x;
> }
> EXPORT(foo);
>
> $ nm vmlinux | grep __crc_foo
> 00000000a0cf13a0 A __crc_foo
>
> Now change to
>
> struct blah {
>   int y;
>   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.o  | grep __crc_foo
s#blah struct blah { int x ; }
foo int foo ( s#blah * )
000000000cd0312e A __crc_foo

but adding y:

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