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

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Date:   Fri, 09 Dec 2016 15:21:33 +0000
From:   Ian Campbell <ijc@...lion.org.uk>
To:     Nicholas Piggin <npiggin@...il.com>, Michal Marek <mmarek@...e.com>
Cc:     Ben Hutchings <ben@...adent.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Adam Borowski <kilobyte@...band.pl>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@...r.kernel.org>,
        Debian kernel maintainers <debian-kernel@...ts.debian.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>, Ingo Molnar <mingo@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Dodji Seketeli <dodji@...eteli.org>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported
 from asm

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.