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

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Date:   Wed, 14 Dec 2016 10:56:56 +0100
From:   Dodji Seketeli <dodji@...eteli.org>
To:     Michal Marek <mmarek@...e.com>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Ian Campbell <ijc@...lion.org.uk>,
        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\@vger.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>
Subject: Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm

Dodji Seketeli <dodji@...eteli.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