From: Dodji Seketeli <dodji@seketeli.org>
To: Michal Marek <mmarek@suse.com>
Cc: Nicholas Piggin <npiggin@gmail.com>, Ian Campbell <ijc@hellion.org.uk>,
        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>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
Organization: Me, myself and I
References: <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>
        <20161210021529.4a6e684f@roar.ozlabs.ibm.com>
        <86vaus3eld.fsf@seketeli.org>
        <f7c5d50d-8930-7ab1-62bb-8a5d0aead988@suse.com>
        <867f72vqec.fsf@seketeli.org> <20161214091539.GA9000@sepie.suse.cz>
        <86twa6svhi.fsf@seketeli.org>
Date: Wed, 14 Dec 2016 10:56:56 +0100
In-Reply-To: <86twa6svhi.fsf@seketeli.org> (Dodji Seketeli's message of "Wed,
        14 Dec 2016 10:36:25 +0100")
Message-ID: <86d1gusujb.fsf@seketeli.org>
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Dodji Seketeli <dodji@seketeli.org> a écrit:

Grr, I did paste the wrong content of t1.c and t2.c in my last message sorry.

Here are the correct ones:

$ cat t1.c
struct s1;
struct s2 {
	int i;
};
struct s3 {
	struct s1 *ptr1;
	struct s2 *ptr2;
};

void foo(struct s3* s __attribute__((unused)))
{
}

$ cat t2.c
struct s1 {
	int j;
};
struct s2;
struct s3 {
	struct s1 *ptr1;
	struct s2 *ptr2;
};

void foo(struct s3* s __attribute__((unused)))
{
}

$ gcc -g -c t1.c
$ gcc -g -c t2.c
$ abidiff t1.o t2.o
$ 

The rest of my previous message still applies :-)

> So, as you see here, abidiff considers t1.o and t2.o has having the same
> ABI, so it considers the two foo functions to be equivalent.
>
>> The types are the same, but their visibility in the different
>> compilation units differs.
>
> I see, for genksyms, the order of declarations matters, especially when
> forward declarations are involved.
>
> Libabigail does a "whole binary" analysis of types.
>
> So, consider the point of use of the type 'struct s1*'.  Even if 'struct
> s' is just forward-declared at that point, the declaration of struct s1
> is "resolved" to its definition.  Even if the definition comes later in
> the binary.
>
> In other words, if struct s1 is defined in the binary, you'll never have
> that "struct s1 {UNKNOWN} *ptr1;" that you see in genksyms's
> representation.

Thanks.

-- 
		Dodji