Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
- To: Ian Campbell <ijc@hellion.org.uk>
- Cc: Michal Marek <mmarek@suse.com>, 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>
- Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
- From: Nicholas Piggin <npiggin@gmail.com>
- Date: Sat, 10 Dec 2016 02:15:29 +1000
- Message-id: <[🔎] 20161210021529.4a6e684f@roar.ozlabs.ibm.com>
- In-reply-to: <[🔎] 1481296893.4509.135.camel@hellion.org.uk>
- 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> <[🔎] 1481296893.4509.135.camel@hellion.org.uk>
On Fri, 09 Dec 2016 15:21:33 +0000
Ian Campbell <ijc@hellion.org.uk> wrote:
> 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.
Aha thanks, well that's my mistake. Clever little bugger, isn't it? Okay
it's not so useless as I first thought!
That said, a dwarf based checker tool should be able to do as good a job
(maybe a bit better because report is very informative and it may pick up
compiler alignments or padding options). So I still think it's worth
looking at those if we can remove modversions.
Thanks,
Nick
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