RepoMirrors/libabigail
1
0
Fork 0
mirror of git://sourceware.org/git/libabigail.git synced 2025-02-10 18:46:54 +00:00
Code Issues Packages Projects Releases Wiki Activity
9418ad46de
libabigail/doc/manuals/libabigail-concepts.rst
Dodji Seketeli ab1fc12f5e Update the manual for variable suppression concepts 
* doc/manuals/libabigail-concepts.rst: Add a section for variable
	suppression specification in the concepts part of the manual.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>
2014-11-01 13:04:15 +01:00

693 lines
21 KiB
ReStructuredText
Raw Blame History

#########
Concepts
#########
.. _abi_artifacts_label:
ABI artifacts
=============
An ABI artifact is a relevant part of the ABI of a shared library or
program. Examples of ABI artifacts are exported types, variables,
functions, or `ELF`_ symbols exported by a shared library.
.. _harmfulchangeconcept_label:
Harmful changes
===============
A change in the diff report is considered harmful if it might cause
ABI compatibility issues. That is, it might prevent an application
dynamically linked against a given version of a library to keep
working with the changed subsequent versions of the same library.
.. _harmlesschangeconcept_label:
Harmless changes
================
A change in the diff report is considered harmless if it will not
cause any ABI compatibility issue. That is, it will not prevent an
application dynamically linked against given version of a library to
keep working with the changed subsequent versions of the same library.
By default, ``abidiff`` filters harmless changes from the diff report.
.. _suppr_spec_label:
Suppression specifications
==========================
* Definition
A suppression specification file is a way for a user to instruct
:ref:`abidiff <abidiff_label>` to avoid emitting reports for changes
involving certain :ref:`ABI artifacts<abi_artifacts_label>`.
It contains directives (or specifications) that describe the set of
ABI artifacts to avoid emitting change reports about.
* Introductory examples
Its syntax is based on a simplified form of `Ini File Syntax`_. For
instance, specify that change reports on a type named FooPrivateType
should be suppressed, one could write this suppression specification:
::
[suppress_type]
name = FooPrivateType
Maybe we want to ensure that only a change reports about structures
named FooPrivateType should be suppressed, one could write: ::
[suppress_type]
type_kind = struct
name = FooPrivateType
But we could also want to suppress change reports avoid typedefs named
FooPrivateType. In that case we would write: ::
[suppress_type]
type_kind = typedef
name = FooPrivateType
Or, we could want to suppress change reports about all struct which
names ends with PrivateType: ::
[suppress_type]
type_kind = struct
name_regexp = ^.*PrivateType
Let's now look at the generic syntax of suppression specification
files.
* Syntax
* Properties
More generally, the format of suppression lists is organized
around the concept of `property`. Every property has a name and
a value, delimited by the ``=`` sign. E.g: ::
name = value
Leading and trailing white spaces are ignored around property
name and values.
.. _suppr_regexp_label:
* Regular expressions
The value of some properties might be a regular expression. In
that case, they must comply with the syntax of `extended POSIX
regular expressions
<http://www.gnu.org/software/findutils/manual/html_node/find_html/posix_002dextended-regular-expression-syntax.html#posix_002dextended-regular-expression-syntax>`_.
Note that Libabigail uses the regular expression engine of the
`GNU C Library`_.
* Escaping a character in a regular expression
When trying to match a string that contains a ``*`` character,
like in the pointer type ``int*``, one must be careful to notice
that the character ``*`` is a special character in the extended
POSIX regular expression syntax. And that character must be
escaped for the regular expression engine. Thus the regular
expression that would match the string ``int*`` in a suppression
file should be ::
int\\*
Wait; but then why the two ``\`` characters? Well, because the
``\`` character is a special character in the `Ini File Syntax`_
used for specifying suppressions. So it must be escaped as
well, so that the Ini File parser leaves a ``\`` character
intact in the data stream that is handed to the regular
expression engine. Hence the ``\\`` targeted at the Ini File
parser.
So, in short, to escape a character in a regular expression,
always prefix the character with the ``\\`` sequence.
* Sections
Properties are then grouped into arbitrarily named sections that
shall not be nested. The name of the section is on a line by
itself and is surrounded by square brackets, i.e: ::
[section_name]
property1_name = property1_value
property2_name = property2_value
A section might or might not have properties. Sections that
expect having properties and which are found nonetheless empty
are just ignored. Properties that are not recognized by the
reader are ignored as well.
* Section names
* ``[suppress_type]``
Suppresses report messages about a type change. The potential
properties of this sections are:
* ``name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving types whose name
matches the regular expression specified as value of this
property.
* ``name`` ``=`` <a-value>
Suppresses change reports involving types whose name
equals the value of this property.
* ``type_kind`` ``=`` ``class`` | ``struct`` | ``union`` |
``enum`` | ``array`` | ``typedef`` | ``builtin``
Suppresses change reports involving a certain kind of
type. The kind of type to suppress change reports for is
specified by the possible values listed above:
- ``class``: suppress change reports for class types.
Note that even if class types don't exist for C, this
value still triggers the suppression of change reports
for struct types, in C. In C++ however, it should do
what it suggests.
- ``struct``: suppress change reports for struct types
in C or C++. Note that the value ``class`` above is a
super-set of this one.
- ``union``: suppress change reports for union types.
- ``enum``: suppress change reports for enum types.
- ``array``: suppress change reports for array types.
- ``typedef``: suppress change reports for typedef types.
- ``builtin``: suppress change reports for built-in (or
native) types. Example of built-in types are char,
int, unsigned int, etc.
.. _suppr_label_property_label:
* ``label`` ``=`` <some-value>
Define a label for the section. A label is just an
informative string that might be used by abidiff to refer
to a type suppression in error messages.
* ``[suppress_function]``
Suppresses report messages about changes on sub-types of a
function. The potential properties of this sections are:
* ``label`` ``=`` <some-value>
This property is the same as the :ref:`label property
<suppr_label_property_label>` defined above.
* ``name`` ``=`` <some-value>
Suppresses change reports involving functions whose name
equals the value of this property.
* ``name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving functions whose name
matches the regular expression specified as value of this
property.
* ``parameter`` ``=`` <function-parameter-specification>
Suppresses change reports involving functions whose
parameters match the parameter specification indicated as
value of this property.
The format of the function parameter specification is:
``'`` ``<parameter-index>`` ``<space>`` ``<type-name-or-regular-expression>``
That is, an apostrophe followed by a number that is the
index of the parameter, followed by one of several spaces,
followed by either the name of the type of the parameter,
or a regular expression describing a family of parameter
type names.
If the parameter type name is designated by a regular
expression, then said regular expression must be enclosed
between two slashes; like ``/some-regular-expression/``.
The index of the first parameter of the function is zero.
Note that for member functions (methods of classes), the
this is the first parameter that comes after the implicit
"this" pointer parameter.
Examples of function parameter specifications are: ::
'0 int
Which means, the parameter at index 0, whose type name is
``int``. ::
'4 unsigned char*
Which means, the parameter at index 4, whose type name is
``unsigned char*``. ::
'2 /^foo.*&/
Which means, the parameter at index 2, whose type name
starts with the string "foo" and ends with an '&'. In
other words, this is the third parameter and it's a
reference on a type that starts with the string "foo".
* ``return_type_name`` ``=`` <some-value>
Suppresses change reports involving functions whose return
type name equals the value of this property.
* ``return_type_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving functions whose return
type name matches the regular expression specified as
value of this property.
* ``symbol_name`` ``=`` <some-value>
Suppresses change reports involving functions whose symbol
name equals the value of this property.
* ``symbol_name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving functions whose symbol
name matches the regular expression specified as value of
this property.
* ``symbol_version`` ``=`` <some-value>
Suppresses change reports involving functions whose symbol
version equals the value of this property.
* ``symbol_version_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving functions whose symbol
version matches the regular expression specified as value
of this property.
* ``[suppress_variable]``
Suppresses report messages about changes on sub-types of a
variable. The potential properties of this sections are:
* ``label`` ``=`` <some-value>
This property is the same as the :ref:`label property
<suppr_label_property_label>` defined above.
* ``name`` ``=`` <some-value>
Suppresses change reports involving variables whose name
equals the value of this property.
* ``name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving variables whose name
matches the regular expression specified as value of this
property.
* ``symbol_name`` ``=`` <some-value>
Suppresses change reports involving variables whose symbol
name equals the value of this property.
* ``symbol_name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving variables whose symbol
name matches the regular expression specified as value of
this property.
* ``symbol_version`` ``=`` <some-value>
Suppresses change reports involving variables whose symbol
version equals the value of this property.
* ``symbol_version_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving variables whose symbol
version matches the regular expression specified as value
of this property.
* ``type_name`` ``=`` <some-value>
Suppresses change reports involving variables whose type
name equals the value of this property.
* ``type_name_regexp`` ``=`` <:ref:`regular-expression <suppr_regexp_label>`>
Suppresses change reports involving variables whose type
name matches the regular expression specified as value of
this property.
* Comments
``;`` or ``#`` ASCII character at the beginning of a line
indicates a comment. Comment lines are ignored.
* Code examples
1. Suppressing change reports about types.
Suppose we have a library named ``libtest1-v0.so`` which
contains this very useful code: ::
$ cat -n test1-v0.cc
1 // A forward declaration for a type considered to be opaque to
2 // function foo() below.
3 struct opaque_type;
4
5 // This function cannot touch any member of opaque_type. Hence,
6 // changes to members of opaque_type should not impact foo, as far as
7 // ABI is concerned.
8 void
9 foo(opaque_type*)
10 {
11 }
12
13 struct opaque_type
14 {
15 int member0;
16 char member1;
17 };
$
Let's change the layout of struct opaque_type by inserting a data
member around line 15, leading to a new version of the library,
that we shall name ``libtest1-v1.so``: ::
$ cat -n test1-v1.cc
1 // A forward declaration for a type considered to be opaque to
2 // function foo() below.
3 struct opaque_type;
4
5 // This function cannot touch any member of opaque_type; Hence,
6 // changes to members of opaque_type should not impact foo, as far as
7 // ABI is concerned.
8 void
9 foo(opaque_type*)
10 {
11 }
12
13 struct opaque_type
14 {
15 char added_member; // <-- a new member got added here now.
16 int member0;
17 char member1;
18 };
$
Let's compile both examples. We shall not forget to compile them
with debug information generation turned on: ::
$ g++ -shared -g -Wall -o libtest1-v0.so test1-v0.cc
$ g++ -shared -g -Wall -o libtest1-v1.so test1-v1.cc
Let's ask :ref:`abidiff <abidiff_label>` which ABI differences it sees
between ``libtest1-v0.so`` and ``libtest1-v1.so``: ::
$ abidiff libtest1-v0.so libtest1-v1.so
Functions changes summary: 0 Removed, 1 Changed, 0 Added function
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
1 function with some indirect sub-type change:
[C]'function void foo(opaque_type*)' has some indirect sub-type changes:
parameter 0 of type 'opaque_type*' has sub-type changes:
in pointed to type 'struct opaque_type':
size changed from 64 to 96 bits
1 data member insertion:
'char opaque_type::added_member', at offset 0 (in bits)
2 data member changes:
'int opaque_type::member0' offset changed from 0 to 32
'char opaque_type::member1' offset changed from 32 to 64
So ``abidiff`` reports that the opaque_type's layout has changed
in a significant way, as far as ABI implications are concerned, in
theory. After all, a sub-type (``struct opaque_type``) of an
exported function (``foo()``) has seen its layout change. This
might have non negligible ABI implications. But in practice here,
the programmer of the litest1-v1.so library knows that the "soft"
contract between the function ``foo()`` and the type ``struct
opaque_type`` is to stay away from the data members of the type.
So layout changes of ``struct opaque_type`` should not impact
``foo()``.
Now to teach ``abidiff`` about this soft contract and have it
avoid emitting what amounts to false positives in this case, we
write the suppression specification file below: ::
$ cat test1.suppr
[suppress_type]
type_kind = struct
name = opaque_type
Translated in plain English, this suppression specification would
read: "Do not emit change reports about a struct which name is
opaque_type".
Let's now invoke ``abidiff`` on the two versions of the library
again, but this time with the suppression specification: ::
$ abidiff --suppressions test1.suppr libtest1-v0.so libtest1-v1.so
Functions changes summary: 0 Removed, 0 Changed (1 filtered out), 0 Added function
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
As you can see, ``abidiff`` does not report the change anymore; it
tells us that it was filtered out instead.
2. Suppressing change reports about functions.
Suppose we have a first version a library named
``libtest2-v0.so`` whose source code is: ::
$ cat -n test2-v0.cc
1 struct S1
2 {
3 int m0;
4
5 S1()
6 : m0()
7 {}
8 };
9
10 struct S2
11 {
12 int m0;
13
14 S2()
15 : m0()
16 {}
17 };
18
19 struct S3
20 {
21 int m0;
22
23 S3()
24 : m0()
25 {}
26 };
27
28 int
29 func(S1&)
30 {
31 // suppose the code does something with the argument.
32 return 0;
33
34 }
35
36 char
37 func(S2*)
38 {
39 // suppose the code does something with the argument.
40 return 0;
41 }
42
43 unsigned
44 func(S3)
45 {
46 // suppose the code does something with the argument.
47 return 0;
48 }
$
And then we come up with a second version ``libtest2-v1.so`` of
that library; the source code is modified by making the
structures ``S1``, ``S2``, ``S3`` inherit another struct: ::
$ cat -n test2-v1.cc
1 struct base_type
2 {
3 int m_inserted;
4 };
5
6 struct S1 : public base_type // <--- S1 now has base_type as its base
7 // type.
8 {
9 int m0;
10
11 S1()
12 : m0()
13 {}
14 };
15
16 struct S2 : public base_type // <--- S2 now has base_type as its base
17 // type.
18 {
19 int m0;
20
21 S2()
22 : m0()
23 {}
24 };
25
26 struct S3 : public base_type // <--- S3 now has base_type as its base
27 // type.
28 {
29 int m0;
30
31 S3()
32 : m0()
33 {}
34 };
35
36 int
37 func(S1&)
38 {
39 // suppose the code does something with the argument.
40 return 0;
41
42 }
43
44 char
45 func(S2*)
46 {
47 // suppose the code does something with the argument.
48 return 0;
49 }
50
51 unsigned
52 func(S3)
53 {
54 // suppose the code does something with the argument.
55 return 0;
56 }
$
Now let's build the two libraries: ::
g++ -Wall -g -shared -o libtest2-v0.so test2-v0.cc
g++ -Wall -g -shared -o libtest2-v0.so test2-v0.cc
Let's look at the output of ``abidiff``: ::
$ abidiff libtest2-v0.so libtest2-v1.so
Functions changes summary: 0 Removed, 3 Changed, 0 Added functions
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
3 functions with some indirect sub-type change:
[C]'function unsigned int func(S3)' has some indirect sub-type changes:
parameter 0 of type 'struct S3' has sub-type changes:
size changed from 32 to 64 bits
1 base class insertion:
struct base_type
1 data member change:
'int S3::m0' offset changed from 0 to 32
[C]'function char func(S2*)' has some indirect sub-type changes:
parameter 0 of type 'S2*' has sub-type changes:
in pointed to type 'struct S2':
size changed from 32 to 64 bits
1 base class insertion:
struct base_type
1 data member change:
'int S2::m0' offset changed from 0 to 32
[C]'function int func(S1&)' has some indirect sub-type changes:
parameter 0 of type 'S1&' has sub-type changes:
in referenced type 'struct S1':
size changed from 32 to 64 bits
1 base class insertion:
struct base_type
1 data member change:
'int S1::m0' offset changed from 0 to 32
$
Let's tell ``abidiff`` to avoid showing us the differences on the
overloads of ``func`` that takes either a pointer or a reference.
For that, we author this simple suppression specification: ::
$ cat -n libtest2.suppr
1 [suppress_function]
2 name = func
3 parameter = '0 S1&
4
5 [suppress_function]
6 name = func
7 parameter = '0 S2*
$
And then let's invoke ``abidiff`` with the suppression
specification: ::
$ ../build/tools/abidiff --suppressions libtest2.suppr libtest2-v0.so libtest2-v1.so
Functions changes summary: 0 Removed, 1 Changed (2 filtered out), 0 Added function
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
1 function with some indirect sub-type change:
[C]'function unsigned int func(S3)' has some indirect sub-type changes:
parameter 0 of type 'struct S3' has sub-type changes:
size changed from 32 to 64 bits
1 base class insertion:
struct base_type
1 data member change:
'int S3::m0' offset changed from 0 to 32
The suppression specification could be reduced using
:ref:`regular expressions <suppr_regexp_label>`: ::
$ cat -n libtest2-1.suppr
1 [suppress_function]
2 name = func
3 parameter = '0 /^S.(&|\\*)/
$
$ ../build/tools/abidiff --suppressions libtest2-1.suppr libtest2-v0.so libtest2-v1.so
Functions changes summary: 0 Removed, 1 Changed (2 filtered out), 0 Added function
Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
1 function with some indirect sub-type change:
[C]'function unsigned int func(S3)' has some indirect sub-type changes:
parameter 0 of type 'struct S3' has sub-type changes:
size changed from 32 to 64 bits
1 base class insertion:
struct base_type
1 data member change:
'int S3::m0' offset changed from 0 to 32
$
.. _ELF: http://en.wikipedia.org/wiki/Executable_and_Linkable_Format
.. _Ini File Syntax: http://en.wikipedia.org/wiki/INI_file
.. _GNU C Library: http://www.gnu.org/software/libc
Reference in New Issue View Git Blame Copy Permalink