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

From	Dodji Seketeli <dodji@seketeli.org>
Newsgroups	linux.debian.kernel, linux.kernel
Subject	Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm
Date	2016-12-14 11:00 +0100
Message-ID	<sOecx-4L4-1@gated-at.bofh.it> (permalink)
References	(6 earlier) <sMw3T-5rk-17@gated-at.bofh.it> <sMCiZ-Cg-9@gated-at.bofh.it> <sO4db-71b-3@gated-at.bofh.it> <sOdJw-4BA-25@gated-at.bofh.it> <sOdTb-4EN-7@gated-at.bofh.it>
Organization	Me, myself and I

Cross-posted to 2 groups.

Show all headers | View raw

Michal Marek <mmarek@suse.com> a écrit:

[...]

> A minimal example would be
>
> t1.c:
> struct s1;
> struct s2 {
> 	int i;
> }
> struct s3 {
> 	struct s1 *ptr1;
> 	struct s2 *ptr2;
> }
> void foo(struct s3*);
> EXPORT_SYMBOL(foo);
>
> t2.c:
> struct s1 {
> 	int j;
> }
> struct s2;
> struct s3 {
> 	struct s1 *ptr1;
> 	struct s2 *ptr2;
> }
> void foo(struct s3*);
> EXPORT_SYMBOL(foo);
>
> genksyms expands this to
> void foo ( struct s3 { struct s1 { UNKNOWN } * ptr1 ; struct s2 { int i ; } * ptr2 ; } * )
>
> or
>
> void foo ( struct s3 { struct s1 { int j ; } * ptr1 ; struct s2 { UNKNOWN } * ptr2 ; } * )
> respectively.

Thanks, I have built an independant test case from this:

$ cat t1.c
struct s1;
struct s2 {
	int i;
};
struct s3 {
	struct s1 *ptr1;
	struct s2 *ptr2;
};
void foo(struct s3*);
$ cat t2.c
struct s1 {
	int j;
};
struct s2;
struct s3 {
	struct s1 *ptr1;
	struct s2 *ptr2;
};
void foo(struct s3*);
$ gcc -g -c t1.c
$ gcc -g -c t2.c
$ abidiff t1.o t2.o
$ 

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.

Cheers,

-- 
		Dodji

Thread

Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 00:10 +0100
  Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 10:20 +0100
    Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 10:40 +0100
      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:00 +0100
      Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:00 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:10 +0100
          Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:20 +0100
            Re: [PATCH] x86/kbuild: enable modversions for symbols exported from  asm Michal Marek <mmarek@suse.com> - 2016-12-14 11:40 +0100
        Re: [PATCH] x86/kbuild: enable modversions for symbols exported from asm Dodji Seketeli <dodji@seketeli.org> - 2016-12-14 11:20 +0100

csiph-web