[PATCH v2] Add regression tests for ctf reading

[Dodji Seketeli]

Hello,

[...]

On Nov 24, 2021, at 8:36 AM, Dodji Seketeli <dodji@seketeli.org> wrote

>> So where exactly is the CTF test disabled?

Guillermo Martinez <guillermo.e.martinez@oracle.com> a écrit:

> I remove those test entries, so the possible problem detected using external diff
> command in CTF is, for instance, in: test-read-common/test-PR26568-1-ctf.o.abi,
> the first time that runtestreadctf is executed an abixml file  is generated:
>
> ...
>     <class-decl name='' size-in-bits='32' alignment-in-bits='32' is-struct='yes' is-anonymous='yes' visibility='default' id='type-id-3'>
>       <data-member access='public' layout-offset-in-bits='0'>
>         <var-decl name='x' type-id='type-id-4' visibility='default'/>
>       </data-member>
>     </class-decl>
>     <class-decl name='' size-in-bits='64' alignment-in-bits='64' is-struct='yes' is-anonymous='yes' visibility='default' id='type-id-5'>
>       <data-member access='public' layout-offset-in-bits='0'>
>         <var-decl name='y' type-id='type-id-6' visibility='default'/>
>       </data-member>
>     </class-decl>
>
> and this is second execution:
> ...
>     <class-decl name='' size-in-bits='64' alignment-in-bits='64' is-struct='yes' is-anonymous='yes' visibility='default' id='type-id-5'>
>       <data-member access='public' layout-offset-in-bits='0'>
>         <var-decl name='y' type-id='type-id-6' visibility='default'/>
>       </data-member>
>     </class-decl>
>     <class-decl name='' size-in-bits='32' alignment-in-bits='32' is-struct='yes' is-anonymous='yes' visibility='default' id='type-id-3'>
>       <data-member access='public' layout-offset-in-bits='0'>
>         <var-decl name='x' type-id='type-id-4' visibility='default'/>
>       </data-member>
>     </class-decl>
>
> As we can see both abixml files  have *same nodes information* but the nodes
> are in a different order, so the test should be marked as passed, however using
> the external diff command the test fails. so my question is should we rely in diff
> command to compare the corpus of the ELF input files (abixml files)?

So, you see here, this is exactly why we use the diff tool IN ADDITION
to abidiff (which only look for ABI changes).

Here, you see that two invocations of abidw is yielding possibly two
*DIFFERENT* abixml files.  They are different because some struct type
definition come out in different order.

Why?

This is because we have two struct types that have the same (empty) name
and yet they are different.  The abixml writer sorts types using their
names, somehow.  So some times, one type comes first; some times, it's
the other.

Let's look at the issue a bit deeper.

These are anonymous struct.

For various reasons, we need to designate types in the Libabigail
system.  So every single type needs to be given a name.  Even anonymous
types.

Most of the time, in C, anonymous types are named using typedefs.  E.g:

typedef struct
{
  int x;
} struct_name;

"typedef struct_name" is the 'naming typedef' of the struct type.  It's
used to name it.  That's how it's designated to be later used.

The libabigail IR has the decl_base::set_naming_typedef() function to
set naming typedefs on 

If you look at the code of the dwarf reader, in the function
build_typedef_type, near the end, you'll see that it uses the
set_naming_typedef method to set the naming typedef of the underlying
anonymous class (or struct) it sees.

Once you've done that, the struct will be represented in the abixml file
as having the name "struct_name".  And your problem will be solved, I
think.

There are other techniques used in the dwarf-reader to handle anonymous
types that are not named by a typedef.  But those are super rare,
especially in C.  So I hope that using naming typedef should be good
enough for a start, in practise.

It's precisely to detect cases like this that the "diff" tool is used.

I hope this helps.

[...]

Cheers,

-- 
		Dodji