Message-ID: <1481296893.4509.135.camel@hellion.org.uk>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported
 from asm
From: Ian Campbell <ijc@hellion.org.uk>
To: Nicholas Piggin <npiggin@gmail.com>, Michal Marek <mmarek@suse.com>
Cc: Ben Hutchings <ben@decadent.org.uk>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Adam Borowski <kilobyte@angband.pl>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Debian kernel maintainers <debian-kernel@lists.debian.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Dodji Seketeli <dodji@seketeli.org>
Date: Fri, 09 Dec 2016 15:21:33 +0000
In-Reply-To: <20161209133308.0acbb57a@roar.ozlabs.ibm.com>
References: <20161129131922.GA31466@angband.pl>
         <20161129135118.24696-1-kilobyte@angband.pl>
         <CA+55aFyZiB4YkwvqzrXO=HD8bcnc2xHkAYrek2QHVnhVvAi3Fw@mail.gmail.com>
         <30bb2db4-47bd-0c35-8328-ef032b551f06@suse.com>
         <CA+55aFxOGw57Gm-QiNs13kfy5k=aRrn3+98415V0g73eGc66mg@mail.gmail.com>
         <20161129195721.GI2697@decadent.org.uk>
         <CA+55aFyQko0t8oMZjhnwhWHrmBUyWjGhsnT=oUOU-W7_04xdzw@mail.gmail.com>
         <20161201051852.28dc335f@roar.ozlabs.ibm.com>
         <CA+55aFzMTrLMrr69ipdaKhz+RJhUu3BxB+kg0689qq_470qEcw@mail.gmail.com>
         <1480541581.16599.78.camel@decadent.org.uk>
         <20161201125545.406d092c@roar.ozlabs.ibm.com>
         <1480559754.16599.92.camel@decadent.org.uk>
         <20161201143928.07a08348@roar.ozlabs.ibm.com>
         <6e8cf20b-2d2f-ba1f-e02c-c757d5a25db7@suse.com>
         <20161209133308.0acbb57a@roar.ozlabs.ibm.com>
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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.