diff mbox series

suppression: Add "has_strict_flexible_array_data_member_conversion" property

Message ID 20231104004757.21305-1-quic_johmoo@quicinc.com
State New
Headers
Series suppression: Add "has_strict_flexible_array_data_member_conversion" property |

Commit Message

John Moon Nov. 4, 2023, 12:47 a.m. UTC 
  From: Dodji Seketeli <dodji@redhat.com>

In the past, it was common to have a "fake flex array" at the end of a
structure. Like this:

Nowadays, with improved compiler support, it's more common to use a real
flex array. As this is a common change which changes ABI representation
in a compatible way, we should have a suppression for it.

For example, if you have a change like this:

struct foo {
    int x;
    int flex[1];
};

...

struct foo {
    int x;
    int flex[];
};

abidiff reports:

  [C] 'struct foo' changed:
    type size changed from 64 to 32 (in bits)
    1 data member change:
      type of 'int flex[1]' changed:
        type name changed from 'int[1]' to 'int[]'
        array type size changed from 32 to 'unknown'
        array type subrange 1 changed length from 1 to 'unknown'

With a new has_strict_flexible_array_data_member_conversion property,
users can specify a suppression which stops abidiff from emitting
this diff for any "fake" flex arrays being converted to real ones:

[suppress_type]
  type_kind = struct
  has_size_change = true
  has_strict_flexible_array_data_member_conversion = true

	* include/abg-fwd.h
	(ir::has_fake_flexible_array_data_member): Declare new accessor
	functions.
	* include/abg-suppression.h
	(type_suppression::{,set_}has_strict_fam_conversion): Declare new
	accessor functions.
	* src/abg-ir.cc
	(ir::has_fake_flexible_array_data_member): Define new accessor
	functions.
	* src/abg-suppression-priv.h
	(type_suppression::priv::has_strict_fam_conv_): Define new
	data member.
	* src/abg-suppression.cc
	(type_suppression::{,set_}has_strict_fam_conversion): Define new
	accessor functions.
	(type_suppression::suppresses_diff): For a type suppression to
	match a fake flex array conversion, has_size_change must be true
	and it must change from a fake flex array to a real flex array.
	(read_type_suppression): Parse the new
	'has_strict_flexible_array_data_member_conversion' property to
	set the type_suppression::set_has_strict_fam_conversion property.
	* doc/manuals/libabigail-concepts.rst: Add an entry for the new
	'has_strict_flexible_array_data_member_conversion' property.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-{1,2}.suppr:
	Add new test suppression files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-{1,2}.txt:
	Add new test reference output files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.c:
	Add source code for new binary test input files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.o:
	Add new binary test input files.
	* tests/data/Makefile.am: Add the new test files to the source
	distribution.
	* tests/test-diff-suppr.cc (in_out_specs): Add the new test input
	files to this test harness.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>
Signed-off-by: John Moon <quic_johmoo@quicinc.com>
---
 doc/manuals/libabigail-concepts.rst           |  26 ++++++++-
 include/abg-fwd.h                             |   9 +++
 include/abg-suppression.h                     |   6 ++
 src/abg-ir.cc                                 |  28 +++++++++
 src/abg-suppression-priv.h                    |   6 +-
 src/abg-suppression.cc                        |  53 ++++++++++++++++--
 ...xible-array-data-member-conversion-1.suppr |   4 ++
 ...xible-array-data-member-conversion-2.suppr |   3 +
 ...-array-data-member-conversion-report-1.txt |   4 ++
 ...-array-data-member-conversion-report-2.txt |  14 +++++
 ...flexible-array-data-member-conversion-v0.c |  11 ++++
 ...flexible-array-data-member-conversion-v0.o | Bin 0 -> 2440 bytes
 ...flexible-array-data-member-conversion-v1.c |  11 ++++
 ...flexible-array-data-member-conversion-v1.o | Bin 0 -> 2432 bytes
 tests/test-diff-suppr.cc                      |  20 +++++++
 15 files changed, 186 insertions(+), 9 deletions(-)
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o

new file mode 100644
index 00000000..95386d41
index 8c9ad070..119be55b 100644

Comments

Dodji Seketeli Nov. 7, 2023, 11:21 a.m. UTC | #1 
Hello,

John Moon <quic_johmoo@quicinc.com> a écrit:

> From: Dodji Seketeli <dodji@redhat.com>

First, thank you for putting together a proper patch from my quick
initial attempt.  That's really appreciated.

[...]

>
> 	* include/abg-fwd.h
> 	(ir::has_fake_flexible_array_data_member): Declare new accessor
> 	functions.
> 	* include/abg-suppression.h
> 	(type_suppression::{,set_}has_strict_fam_conversion): Declare new
> 	accessor functions.
> 	* src/abg-ir.cc
> 	(ir::has_fake_flexible_array_data_member): Define new accessor
> 	functions.
> 	* src/abg-suppression-priv.h
> 	(type_suppression::priv::has_strict_fam_conv_): Define new
> 	data member.
> 	* src/abg-suppression.cc
> 	(type_suppression::{,set_}has_strict_fam_conversion): Define new
> 	accessor functions.
> 	(type_suppression::suppresses_diff): For a type suppression to
> 	match a fake flex array conversion, has_size_change must be true
> 	and it must change from a fake flex array to a real flex array.
> 	(read_type_suppression): Parse the new
> 	'has_strict_flexible_array_data_member_conversion' property to
> 	set the type_suppression::set_has_strict_fam_conversion property.
> 	* doc/manuals/libabigail-concepts.rst: Add an entry for the new
> 	'has_strict_flexible_array_data_member_conversion' property.
> 	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-{1,2}.suppr:
> 	Add new test suppression files.
> 	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-{1,2}.txt:
> 	Add new test reference output files.
> 	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.c:
> 	Add source code for new binary test input files.
> 	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.o:
> 	Add new binary test input files.
> 	* tests/data/Makefile.am: Add the new test files to the source
> 	distribution.

Changes to the tests/data/Makefile.am file were not included in the
patch.  So make distcheck failed.  I have added those changes in.

[...]


> diff --git a/doc/manuals/libabigail-concepts.rst b/doc/manuals/libabigail-concepts.rst
> index 28e71684..f9e27ff9 100644
> --- a/doc/manuals/libabigail-concepts.rst
> +++ b/doc/manuals/libabigail-concepts.rst

Many thanks for adding documentation here.  It's really appreciated!

> @@ -619,9 +619,28 @@ names start with the string "private_data_member".
>  	  {72, end}
>       }
>  
> +.. _suppr_has_strict_flexible_array_data_member_conversion_label:
>  
>  
> - .. _suppr_has_size_change_property_label:
> +* ``has_strict_flexible_array_data_member_conversion``
> +
> + Usage:
> +
> +   ``has_strict_flexible_array_data_member_conversion`` ``=`` yes | no
> +
> + Suppresses change reports involving a type which has a "fake"
> + flexible array member at the end of the struct which is converted
> + to a real flexible array member. This would be a member like
> + ``data[1]`` being converted to ``data[]``.

Nice.

> +
> + Please note: a conversion to a flex array like this
> + will *always* result in the structure changing size,
> + so the suppression will not take effect unless the
> + :ref:`has_size_change<suppr_has_size_change_property_label>`
> + property is present and set to ``yes``.

I have just updated this slightly in regard of the discussion we've had
at https://sourceware.org/bugzilla/show_bug.cgi?id=31017#c3.

Here is what I have replaced the hunk above with:

    + Please note that if the size of the type changed, then the type
    + change will *NOT* be suppressed by the evaluation of this property,
    + unless the
    + :ref:`has_size_change<suppr_has_size_change_property_label>` property
    + is present and set to ``yes``.

[...]

> diff --git a/src/abg-ir.cc b/src/abg-ir.cc
> index 4a652b0f..7ba7f72d 100644
> --- a/src/abg-ir.cc
> +++ b/src/abg-ir.cc
> @@ -10822,6 +10822,34 @@ var_decl_sptr
>  has_flexible_array_data_member(const class_decl_sptr& klass)
>  {return has_flexible_array_data_member(klass.get());}
>  
> +var_decl_sptr
> +has_fake_flexible_array_data_member(const class_decl& klass)

I have added doxygen comments to this function as I haven't done it
initially.

[...]

> +
> +var_decl_sptr
> +has_fake_flexible_array_data_member(const class_decl* klass)

Likewise.

> +{return has_fake_flexible_array_data_member(*klass);}
> +
> +var_decl_sptr
> +has_fake_flexible_array_data_member(const class_decl_sptr& klass)

Likewise.

> +{return has_fake_flexible_array_data_member(klass.get());}
> +
>  /// Test wheter a type is a declaration-only class.
>  ///
>  /// @param t the type to considier.

[...]


> --- a/src/abg-suppression.cc
> +++ b/src/abg-suppression.cc
> @@ -808,6 +808,14 @@ void
>  type_suppression::set_changed_enumerators_regexp(const vector<regex::regex_t_sptr>& n)
>  {priv_->changed_enumerators_regexp_ = n;}
>  
> +bool
> +type_suppression::has_strict_fam_conversion () const

Likewise.

> +{return priv_->has_strict_fam_conv_;}
> +
> +void
> +type_suppression::set_has_strict_fam_conversion(bool f)

Likewise.

> +{priv_->has_strict_fam_conv_ = f;}
> +

[...]

> @@ -1027,6 +1037,28 @@ type_suppression::suppresses_diff(const diff* diff) const
>  	  else
>  	    return false;
>  	}
> +
> +      // Support for the
> +      // "has_strict_flexible_array_data_member_conversion = true"
> +      // clause.
> +      if (has_strict_fam_conversion())
> +	{
> +	  // Let's detect if the first class of the diff has a fake
> +	  // flexible array data member that got turned into a real
> +	  // flexible array data member.
> +	  if (!(
> +		(get_has_size_change())
> +		// This situation will always result in a size change,
> +		// so check that "has_size_change = true" before
> +		// processing further
> +		&&
> +		(has_fake_flexible_array_data_member(first_class)
> +		 && has_flexible_array_data_member(second_class))
> +		// A fake flexible array member has been changed into
> +		// a real flexible array ...
> +		))
> +	    return false;
> +	}

Following our discussion at
https://sourceware.org/bugzilla/show_bug.cgi?id=31017#c3, I replaced the
hunk above with this one:

+      if (has_strict_fam_conversion())
+	{
+	  // Let's detect if the first class of the diff has a fake
+	  // flexible array data member that got turned into a real
+	  // flexible array data member.
+	  if (!((get_has_size_change() || ((first_class->get_size_in_bits()
+					    == second_class->get_size_in_bits())))
+		&& filtering::has_strict_fam_conversion(klass_diff)))
+	    return false;
+	}

The new filtering::has_strict_fam_conversion function was introduced
to encapsulate the detection of a strict fam conversion and it's in
abg-comp-filter.cc.

>      }

[...]

> diff --git a/tests/test-diff-suppr.cc b/tests/test-diff-suppr.cc
> index 8c9ad070..119be55b 100644
> --- a/tests/test-diff-suppr.cc
> +++ b/tests/test-diff-suppr.cc
> @@ -2376,6 +2376,26 @@ InOutSpec in_out_specs[] =
>      "data/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt",
>      "output/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt"
>    },
> +  {
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
> +    "",
> +    "",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr",
> +    "--drop-private-types --no-default-suppression --non-reachable-types",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
> +    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
> +  },
> +  {
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
> +    "",
> +    "",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr",
> +    "--drop-private-types --no-default-suppression --non-reachable-types",
> +    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
> +    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
> +  },
>    // This should be the last entry
>    {NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL}
>  };

Thanks for adding these tests!  It's really appreciated!

Please find below the amended patch.  It passes "make distcheck" and I
have updated the WIP branch users/dodji/PR31017 with it. What do you
think?

From fe1dbee8e8c5211c910d9b72fccd1230600be4ab Mon Sep 17 00:00:00 2001
From: Dodji Seketeli <dodji@redhat.com>
Date: Fri, 3 Nov 2023 17:47:57 -0700
Subject: [PATCH] suppression: Add
 "has_strict_flexible_array_data_member_conversion" property

In the past, it was common to have a "fake flex array" at the end of a
structure. Like this:

Nowadays, with improved compiler support, it's more common to use a real
flex array. As this is a common change which changes ABI representation
in a compatible way, we should have a suppression for it.

For example, if you have a change like this:

struct foo {
    int x;
    int flex[1];
};

...

struct foo {
    int x;
    int flex[];
};

abidiff reports:

  [C] 'struct foo' changed:
    type size changed from 64 to 32 (in bits)
    1 data member change:
      type of 'int flex[1]' changed:
        type name changed from 'int[1]' to 'int[]'
        array type size changed from 32 to 'unknown'
        array type subrange 1 changed length from 1 to 'unknown'

With a new has_strict_flexible_array_data_member_conversion property,
users can specify a suppression which stops abidiff from emitting
this diff for any "fake" flex arrays being converted to real ones:

[suppress_type]
  type_kind = struct
  has_size_change = true
  has_strict_flexible_array_data_member_conversion = true

	* include/abg-comp-filter.h (has_strict_fam_conversion): Declare
	new functions.
	* include/abg-fwd.h
	(ir::has_fake_flexible_array_data_member): Declare new accessor
	functions.
	* include/abg-suppression.h
	(type_suppression::{,set_}has_strict_fam_conversion): Declare new
	accessor functions.
	* src/abg-comp-filter.cc (has_strict_fam_conversion): Define new
	functions.
	* src/abg-ir.cc
	(ir::has_fake_flexible_array_data_member): Define new accessor
	functions.
	* src/abg-suppression-priv.h
	(type_suppression::priv::has_strict_fam_conv_): Define new
	data member.
	* src/abg-suppression.cc
	(type_suppression::{,set_}has_strict_fam_conversion): Define new
	accessor functions.
	(type_suppression::suppresses_diff): For a type suppression to
	match a fake flex array conversion, either the size of the type
	hasn't change or has_size_change must be true and then the type
	must change from a fake flex array to a real flex array.
	(read_type_suppression): Parse the new
	'has_strict_flexible_array_data_member_conversion' property to
	set the type_suppression::set_has_strict_fam_conversion property.
	* doc/manuals/libabigail-concepts.rst: Add an entry for the new
	'has_strict_flexible_array_data_member_conversion' property.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-{1,2}.suppr:
	Add new test suppression files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-{1,2}.txt:
	Add new test reference output files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.c:
	Add source code for new binary test input files.
	* tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v{0,1}.o:
	Add new binary test input files.
	* tests/data/Makefile.am: Add the new test files to the source
	distribution.
	* tests/test-diff-suppr.cc (in_out_specs): Add the new test input
	files to this test harness.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>
Signed-off-by: John Moon <quic_johmoo@quicinc.com>
---
 doc/manuals/libabigail-concepts.rst           |  26 +++++-
 include/abg-comp-filter.h                     |   7 ++
 include/abg-fwd.h                             |   9 ++
 include/abg-suppression.h                     |   6 ++
 src/abg-comp-filter.cc                        |  49 +++++++++++
 src/abg-ir.cc                                 |  83 +++++++++++++++++-
 src/abg-suppression-priv.h                    |   6 +-
 src/abg-suppression.cc                        |  52 +++++++++--
 tests/data/Makefile.am                        |   8 ++
 ...xible-array-data-member-conversion-1.suppr |   4 +
 ...xible-array-data-member-conversion-2.suppr |   3 +
 ...-array-data-member-conversion-report-1.txt |   4 +
 ...-array-data-member-conversion-report-2.txt |  14 +++
 ...flexible-array-data-member-conversion-v0.c |  11 +++
 ...flexible-array-data-member-conversion-v0.o | Bin 0 -> 2440 bytes
 ...flexible-array-data-member-conversion-v1.c |  11 +++
 ...flexible-array-data-member-conversion-v1.o | Bin 0 -> 2432 bytes
 tests/test-diff-suppr.cc                      |  20 +++++
 18 files changed, 303 insertions(+), 10 deletions(-)
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
 create mode 100644 tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o

diff --git a/doc/manuals/libabigail-concepts.rst b/doc/manuals/libabigail-concepts.rst
index 28e71684..7b73aaa8 100644
--- a/doc/manuals/libabigail-concepts.rst
+++ b/doc/manuals/libabigail-concepts.rst
@@ -619,9 +619,28 @@ names start with the string "private_data_member".
 	  {72, end}
      }
 
+.. _suppr_has_strict_flexible_array_data_member_conversion_label:
 
 
- .. _suppr_has_size_change_property_label:
+* ``has_strict_flexible_array_data_member_conversion``
+
+ Usage:
+
+   ``has_strict_flexible_array_data_member_conversion`` ``=`` yes | no
+
+ Suppresses change reports involving a type which has a "fake"
+ flexible array member at the end of the struct which is converted
+ to a real flexible array member. This would be a member like
+ ``data[1]`` being converted to ``data[]``.
+
+ Please note that if the size of the type changed, then the type
+ change will *NOT* be suppressed by the evaluation of this property,
+ unless the
+ :ref:`has_size_change<suppr_has_size_change_property_label>` property
+ is present and set to ``yes``.
+
+.. _suppr_has_size_change_property_label:
+
 
 * ``has_size_change``
 
@@ -631,9 +650,10 @@ names start with the string "private_data_member".
 
 
 This property is to be used in conjunction with the properties
-:ref:`has_data_member_inserted_between<suppr_has_data_member_inserted_between_label>`
+:ref:`has_data_member_inserted_between<suppr_has_data_member_inserted_between_label>`,
+:ref:`has_data_members_inserted_between<suppr_has_data_members_inserted_between_label>`,
 and
-:ref:`has_data_members_inserted_between<suppr_has_data_members_inserted_between_label>`.
+:ref:`has_strict_flexible_array_data_member_conversion<suppr_has_strict_flexible_array_data_member_conversion_label>`
 Those properties will not match a type change if the size of the type
 changes, unless the ``has_size_changes`` property is set to ``yes``.
 
diff --git a/include/abg-comp-filter.h b/include/abg-comp-filter.h
index cd12b314..8d11fdd2 100644
--- a/include/abg-comp-filter.h
+++ b/include/abg-comp-filter.h
@@ -98,6 +98,13 @@ bool
 is_var_1_dim_unknown_size_array_change(const var_decl_sptr& var1,
 				       const var_decl_sptr& var2);
 
+bool
+has_strict_fam_conversion(const class_decl_sptr& first,
+			  const class_decl_sptr& second);
+
+bool
+has_strict_fam_conversion(const diff *d);
+
 struct filter_base;
 /// Convenience typedef for a shared pointer to filter_base
 typedef shared_ptr<filter_base> filter_base_sptr;
diff --git a/include/abg-fwd.h b/include/abg-fwd.h
index 7d6637b9..de5b72b0 100644
--- a/include/abg-fwd.h
+++ b/include/abg-fwd.h
@@ -490,6 +490,15 @@ has_flexible_array_data_member(const class_decl*);
 var_decl_sptr
 has_flexible_array_data_member(const class_decl_sptr&);
 
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl&);
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl*);
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl_sptr&);
+
 bool
 is_declaration_only_class_or_union_type(const type_base *t,
 					bool look_through_decl_only = false);
diff --git a/include/abg-suppression.h b/include/abg-suppression.h
index 996600bb..dd0870bc 100644
--- a/include/abg-suppression.h
+++ b/include/abg-suppression.h
@@ -336,6 +336,12 @@ public:
   void
   set_changed_enumerators_regexp(const vector<regex::regex_t_sptr>&);
 
+  bool
+  has_strict_fam_conversion () const;
+
+  void
+  set_has_strict_fam_conversion(bool);
+
   virtual bool
   suppresses_diff(const diff* diff) const;
 
diff --git a/src/abg-comp-filter.cc b/src/abg-comp-filter.cc
index e02e9430..82a819d6 100644
--- a/src/abg-comp-filter.cc
+++ b/src/abg-comp-filter.cc
@@ -712,6 +712,55 @@ is_var_1_dim_unknown_size_array_change(const diff* diff)
   return is_var_1_dim_unknown_size_array_change(f, s);
 }
 
+/// Test if a class with a fake flexible data member got changed into
+/// a class with a real fexible data member.
+///
+/// A fake flexible array data member is a data member that is the
+/// last of the class/struct which type is an array of one element.
+/// This was used before C99 standardized flexible array data members.
+///
+/// @param first the first version of the class to consider.
+///
+/// @param second the second version of the class to consider.
+///
+/// @return true iff @p first has a fake flexible array data member
+/// that got changed into @p second with a real flexible array data
+/// member.
+bool
+has_strict_fam_conversion(const class_decl_sptr& first,
+			  const class_decl_sptr& second)
+{
+  if (has_fake_flexible_array_data_member(first)
+      && has_flexible_array_data_member(second))
+    // A fake flexible array member has been changed into
+    // a real flexible array ...
+    return true;
+  return false;
+}
+
+/// Test if a diff node carries a change from class with a fake
+/// flexible data member into a class with a real fexible data member.
+///
+/// A fake flexible array data member is a data member that is the
+/// last of the class/struct which type is an array of one element.
+/// This was used before C99 standardized flexible array data members.
+///
+/// @param the diff node to consider.
+///
+/// @return true iff @p dif carries a change from class with a fake
+/// flexible data member into a class with a real fexible data member.
+/// member.
+bool
+has_strict_fam_conversion(const diff *dif)
+{
+  const class_diff* d = is_class_diff(dif);
+  if (!d)
+    return false;
+
+  return has_strict_fam_conversion(d->first_class_decl(),
+				   d->second_class_decl());
+}
+
 /// Test if a class_diff node has static members added or removed.
 ///
 /// @param diff the diff node to consider.
diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 4a652b0f..50a4e0ab 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -10822,6 +10822,88 @@ var_decl_sptr
 has_flexible_array_data_member(const class_decl_sptr& klass)
 {return has_flexible_array_data_member(klass.get());}
 
+/// Test if the last data member of a class is an array with
+/// one element.
+///
+/// An array with one element is a way to mimic the flexible data
+/// member idiom that was later standardized in C99.
+///
+/// To learn more about the flexible data member idiom, please
+/// consider reading :
+/// https://en.wikipedia.org/wiki/Flexible_array_member.
+///
+/// The various ways of representing that idiom pre-standardization
+/// are presented in this article:
+/// https://developers.redhat.com/articles/2022/09/29/benefits-limitations-flexible-array-members#
+///
+/// @param klass the class to consider.
+///
+/// @return the data member which type is a fake flexible array, if
+/// any, or nil.
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl& klass)
+{
+  var_decl_sptr nil;
+  const class_or_union::data_members& dms = klass.get_data_members();
+  if (dms.empty())
+    return nil;
+
+  if (array_type_def_sptr array = is_array_type(dms.back()->get_type()))
+    {// The type of the last data member is an array.
+      if (array->get_subranges().size() == 1
+	  && array->get_subranges()[0]->get_length() == 1)
+	// The array has a size of one. We are thus looking at a
+	// "fake" flexible array data member.  Let's return it.
+	return dms.back();
+    }
+
+  return nil;
+}
+
+/// Test if the last data member of a class is an array with
+/// one element.
+///
+/// An array with one element is a way to mimic the flexible data
+/// member idiom that was later standardized in C99.
+///
+/// To learn more about the flexible data member idiom, please
+/// consider reading :
+/// https://en.wikipedia.org/wiki/Flexible_array_member.
+///
+/// The various ways of representing that idiom pre-standardization
+/// are presented in this article:
+/// https://developers.redhat.com/articles/2022/09/29/benefits-limitations-flexible-array-members#
+///
+/// @param klass the class to consider.
+///
+/// @return the data member which type is a fake flexible array, if
+/// any, or nil.
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl* klass)
+{return has_fake_flexible_array_data_member(*klass);}
+
+/// Test if the last data member of a class is an array with
+/// one element.
+///
+/// An array with one element is a way to mimic the flexible data
+/// member idiom that was later standardized in C99.
+///
+/// To learn more about the flexible data member idiom, please
+/// consider reading :
+/// https://en.wikipedia.org/wiki/Flexible_array_member.
+///
+/// The various ways of representing that idiom pre-standardization
+/// are presented in this article:
+/// https://developers.redhat.com/articles/2022/09/29/benefits-limitations-flexible-array-members#
+///
+/// @param klass the class to consider.
+///
+/// @return the data member which type is a fake flexible array, if
+/// any, or nil.
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl_sptr& klass)
+{return has_fake_flexible_array_data_member(klass.get());}
+
 /// Test wheter a type is a declaration-only class.
 ///
 /// @param t the type to considier.
@@ -10844,7 +10926,6 @@ is_declaration_only_class_or_union_type(const type_base *t,
   return false;
 }
 
-
 /// Test wheter a type is a declaration-only class.
 ///
 /// @param t the type to considier.
diff --git a/src/abg-suppression-priv.h b/src/abg-suppression-priv.h
index 351c5965..e4d65df8 100644
--- a/src/abg-suppression-priv.h
+++ b/src/abg-suppression-priv.h
@@ -586,6 +586,9 @@ class type_suppression::priv
   mutable regex::regex_t_sptr		source_location_to_keep_regex_;
   mutable vector<string>		changed_enumerator_names_;
   mutable vector<regex::regex_t_sptr>	changed_enumerators_regexp_;
+  // Whether the "has_strict_flexible_array_data_member_conversion"
+  // property was set.
+  bool					has_strict_fam_conv_;
 
   priv();
 
@@ -602,7 +605,8 @@ public:
       type_kind_(type_kind),
       consider_reach_kind_(consider_reach_kind),
       reach_kind_(reach_kind),
-      has_size_change_(false)
+      has_size_change_(false),
+      has_strict_fam_conv_(false)
   {}
 
   /// Get the regular expression object associated to the 'type_name_regex'
diff --git a/src/abg-suppression.cc b/src/abg-suppression.cc
index 326d003e..0fb6d057 100644
--- a/src/abg-suppression.cc
+++ b/src/abg-suppression.cc
@@ -808,6 +808,21 @@ void
 type_suppression::set_changed_enumerators_regexp(const vector<regex::regex_t_sptr>& n)
 {priv_->changed_enumerators_regexp_ = n;}
 
+/// Getter of the "has_string_fam_conversion" property.
+///
+/// @return the value of the "has_string_fam_conversion" property.
+bool
+type_suppression::has_strict_fam_conversion () const
+{return priv_->has_strict_fam_conv_;}
+
+/// Setter of the "has_string_fam_conversion" property.
+///
+/// @param f the new value of the "has_string_fam_conversion"
+/// property.
+void
+type_suppression::set_has_strict_fam_conversion(bool f)
+{priv_->has_strict_fam_conv_ = f;}
+
 /// Evaluate this suppression specification on a given diff node and
 /// say if the diff node should be suppressed or not.
 ///
@@ -967,6 +982,11 @@ type_suppression::suppresses_diff(const diff* diff) const
   const class_diff* klass_diff = dynamic_cast<const class_diff*>(d);
   if (klass_diff)
     {
+      const class_decl_sptr& first_class =
+	klass_diff->first_class_decl();
+      const class_decl_sptr& second_class =
+	klass_diff->second_class_decl();
+
       // We are looking at a class diff ...
       if (!get_data_member_insertion_ranges().empty())
 	{
@@ -981,9 +1001,6 @@ type_suppression::suppresses_diff(const diff* diff) const
 	      // that suppression applies to types that have size
 	      // change.
 
-	      const class_decl_sptr& first_type_decl =
-		klass_diff->first_class_decl();
-
 	      if (klass_diff->inserted_data_members().empty()
 		  && klass_diff->changed_data_members().empty())
 		// So there is a has_data_member_inserted_* clause,
@@ -1001,7 +1018,7 @@ type_suppression::suppresses_diff(const diff* diff) const
 		  for (const auto& range : get_data_member_insertion_ranges())
 		    if (is_data_member_offset_in_range(is_var_decl(member),
 						       range,
-						       first_type_decl.get()))
+						       first_class.get()))
 		      matched = true;
 
 		  if (!matched)
@@ -1017,7 +1034,7 @@ type_suppression::suppresses_diff(const diff* diff) const
 
 		  for (const auto& range : get_data_member_insertion_ranges())
 		    if (is_data_member_offset_in_range(member, range,
-						       first_type_decl.get()))
+						       first_class.get()))
 		      matched = true;
 
 		  if (!matched)
@@ -1027,6 +1044,20 @@ type_suppression::suppresses_diff(const diff* diff) const
 	  else
 	    return false;
 	}
+
+      // Support for the
+      // "has_strict_flexible_array_data_member_conversion = true"
+      // clause.
+      if (has_strict_fam_conversion())
+	{
+	  // Let's detect if the first class of the diff has a fake
+	  // flexible array data member that got turned into a real
+	  // flexible array data member.
+	  if (!((get_has_size_change() || ((first_class->get_size_in_bits()
+					    == second_class->get_size_in_bits())))
+		&& filtering::has_strict_fam_conversion(klass_diff)))
+	    return false;
+	}
     }
 
   const enum_diff* enum_dif = dynamic_cast<const enum_diff*>(d);
@@ -2321,6 +2352,14 @@ read_type_suppression(const ini::config::section& section)
       }
     }
 
+  // Support "has_strict_flexible_array_data_member_conversion"
+  ini::simple_property_sptr has_strict_fam_conv =
+    is_simple_property
+    (section.find_property("has_strict_flexible_array_data_member_conversion"));
+  string has_strict_fam_conv_str = has_strict_fam_conv
+    ? has_strict_fam_conv->get_value()->as_string()
+    : "";
+
   if (section.get_name() == "suppress_type")
     result.reset(new type_suppression(label_str, name_regex_str, name_str));
   else if (section.get_name() == "allow_type")
@@ -2388,6 +2427,9 @@ read_type_suppression(const ini::config::section& section)
       && !changed_enumerators_regexp.empty())
     result->set_changed_enumerators_regexp(changed_enumerators_regexp);
 
+  if (has_strict_fam_conv_str == "yes" || has_strict_fam_conv_str == "true")
+    result->set_has_strict_fam_conversion(true);
+
   return result;
 }
 
diff --git a/tests/data/Makefile.am b/tests/data/Makefile.am
index 945831ff..28d767d5 100644
--- a/tests/data/Makefile.am
+++ b/tests/data/Makefile.am
@@ -1930,6 +1930,14 @@ test-diff-suppr/test-has-data-member-inserted-at-1-v0.o \
 test-diff-suppr/test-has-data-member-inserted-at-1-v1.c \
 test-diff-suppr/test-has-data-member-inserted-at-1-v1.o \
 test-diff-suppr/test-has-data-member-inserted-at-1.1.suppr \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o \
+test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o \
 \
 test-diff-dwarf-abixml/test0-pr19026-libvtkIOSQL-6.1.so.1 \
 test-diff-dwarf-abixml/test0-pr19026-libvtkIOSQL-6.1.so.1.abi \
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
new file mode 100644
index 00000000..5cb8d880
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
@@ -0,0 +1,4 @@
+[suppress_type]
+  type_kind = struct
+  has_size_change = true
+  has_strict_flexible_array_data_member_conversion = true
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
new file mode 100644
index 00000000..384409d0
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
@@ -0,0 +1,3 @@
+[suppress_type]
+  type_kind = struct
+  has_strict_flexible_array_data_member_conversion = true
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
new file mode 100644
index 00000000..b4ea5bf1
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
@@ -0,0 +1,4 @@
+Functions changes summary: 0 Removed, 0 Changed, 0 Added function
+Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
+Unreachable types summary: 0 removed, 0 changed (1 filtered out), 0 added type
+
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
new file mode 100644
index 00000000..2352dd4e
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
@@ -0,0 +1,14 @@
+Functions changes summary: 0 Removed, 0 Changed, 0 Added function
+Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
+Unreachable types summary: 0 removed, 1 changed, 0 added type
+
+1 changed type unreachable from any public interface:
+
+  [C] 'struct foo' changed:
+    type size changed from 64 to 32 (in bits)
+    1 data member change:
+      type of 'int flex[1]' changed:
+        type name changed from 'int[1]' to 'int[]'
+        array type size changed from 32 to 'unknown'
+        array type subrange 1 changed length from 1 to 'unknown'
+
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
new file mode 100644
index 00000000..1397cd52
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
@@ -0,0 +1,11 @@
+/*
+ * Compile this with:
+ *   gcc -g -c test-has-strict-flexible-array-data-member-conversion-v0.c
+ */
+struct foo
+{
+  int x;
+  int flex[1];
+};
+
+struct foo S;
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o
new file mode 100644
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diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
new file mode 100644
index 00000000..95386d41
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
@@ -0,0 +1,11 @@
+/*
+ * Compile this with:
+ *   gcc -g -c test-has-strict-flexible-array-data-member-conversion-v1.c
+ */
+struct foo
+{
+  int x;
+  int flex[];
+};
+
+struct foo S;
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o
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zagkTxq^G%x_!<wu|Mlp7knfM)7`b<8?;{Sbkdh!dKfQZt@jv+Y`<#d+QI7uuX6xT{

literal 0
HcmV?d00001

diff --git a/tests/test-diff-suppr.cc b/tests/test-diff-suppr.cc
index 8c9ad070..119be55b 100644
--- a/tests/test-diff-suppr.cc
+++ b/tests/test-diff-suppr.cc
@@ -2376,6 +2376,26 @@ InOutSpec in_out_specs[] =
     "data/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt",
     "output/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt"
   },
+  {
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
+    "",
+    "",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr",
+    "--drop-private-types --no-default-suppression --non-reachable-types",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
+    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
+  },
+  {
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
+    "",
+    "",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr",
+    "--drop-private-types --no-default-suppression --non-reachable-types",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
+    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
+  },
   // This should be the last entry
   {NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL}
 };
diff mbox series

Patch

diff --git a/doc/manuals/libabigail-concepts.rst b/doc/manuals/libabigail-concepts.rst
index 28e71684..f9e27ff9 100644
--- a/doc/manuals/libabigail-concepts.rst
+++ b/doc/manuals/libabigail-concepts.rst
@@ -619,9 +619,28 @@  names start with the string "private_data_member".
 	  {72, end}
      }
 
+.. _suppr_has_strict_flexible_array_data_member_conversion_label:
 
 
- .. _suppr_has_size_change_property_label:
+* ``has_strict_flexible_array_data_member_conversion``
+
+ Usage:
+
+   ``has_strict_flexible_array_data_member_conversion`` ``=`` yes | no
+
+ Suppresses change reports involving a type which has a "fake"
+ flexible array member at the end of the struct which is converted
+ to a real flexible array member. This would be a member like
+ ``data[1]`` being converted to ``data[]``.
+
+ Please note: a conversion to a flex array like this
+ will *always* result in the structure changing size,
+ so the suppression will not take effect unless the
+ :ref:`has_size_change<suppr_has_size_change_property_label>`
+ property is present and set to ``yes``.
+
+.. _suppr_has_size_change_property_label:
+
 
 * ``has_size_change``
 
@@ -631,9 +650,10 @@  names start with the string "private_data_member".
 
 
 This property is to be used in conjunction with the properties
-:ref:`has_data_member_inserted_between<suppr_has_data_member_inserted_between_label>`
+:ref:`has_data_member_inserted_between<suppr_has_data_member_inserted_between_label>`,
+:ref:`has_data_members_inserted_between<suppr_has_data_members_inserted_between_label>`,
 and
-:ref:`has_data_members_inserted_between<suppr_has_data_members_inserted_between_label>`.
+:ref:`has_strict_flexible_array_data_member_conversion<suppr_has_strict_flexible_array_data_member_conversion_label>`
 Those properties will not match a type change if the size of the type
 changes, unless the ``has_size_changes`` property is set to ``yes``.
 
diff --git a/include/abg-fwd.h b/include/abg-fwd.h
index 7d6637b9..de5b72b0 100644
--- a/include/abg-fwd.h
+++ b/include/abg-fwd.h
@@ -490,6 +490,15 @@  has_flexible_array_data_member(const class_decl*);
 var_decl_sptr
 has_flexible_array_data_member(const class_decl_sptr&);
 
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl&);
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl*);
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl_sptr&);
+
 bool
 is_declaration_only_class_or_union_type(const type_base *t,
 					bool look_through_decl_only = false);
diff --git a/include/abg-suppression.h b/include/abg-suppression.h
index 996600bb..dd0870bc 100644
--- a/include/abg-suppression.h
+++ b/include/abg-suppression.h
@@ -336,6 +336,12 @@  public:
   void
   set_changed_enumerators_regexp(const vector<regex::regex_t_sptr>&);
 
+  bool
+  has_strict_fam_conversion () const;
+
+  void
+  set_has_strict_fam_conversion(bool);
+
   virtual bool
   suppresses_diff(const diff* diff) const;
 
diff --git a/src/abg-ir.cc b/src/abg-ir.cc
index 4a652b0f..7ba7f72d 100644
--- a/src/abg-ir.cc
+++ b/src/abg-ir.cc
@@ -10822,6 +10822,34 @@  var_decl_sptr
 has_flexible_array_data_member(const class_decl_sptr& klass)
 {return has_flexible_array_data_member(klass.get());}
 
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl& klass)
+{
+  var_decl_sptr nil;
+  const class_or_union::data_members& dms = klass.get_data_members();
+  if (dms.empty())
+    return nil;
+
+  if (array_type_def_sptr array = is_array_type(dms.back()->get_type()))
+    {// The type of the last data member is an array.
+      if (array->get_subranges().size() == 1
+	  && array->get_subranges()[0]->get_length() == 1)
+	// The array has a size of one. We are thus looking at a
+	// "fake" flexible array data member.  Let's return it.
+	return dms.back();
+    }
+
+  return nil;
+}
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl* klass)
+{return has_fake_flexible_array_data_member(*klass);}
+
+var_decl_sptr
+has_fake_flexible_array_data_member(const class_decl_sptr& klass)
+{return has_fake_flexible_array_data_member(klass.get());}
+
 /// Test wheter a type is a declaration-only class.
 ///
 /// @param t the type to considier.
diff --git a/src/abg-suppression-priv.h b/src/abg-suppression-priv.h
index 351c5965..e4d65df8 100644
--- a/src/abg-suppression-priv.h
+++ b/src/abg-suppression-priv.h
@@ -586,6 +586,9 @@  class type_suppression::priv
   mutable regex::regex_t_sptr		source_location_to_keep_regex_;
   mutable vector<string>		changed_enumerator_names_;
   mutable vector<regex::regex_t_sptr>	changed_enumerators_regexp_;
+  // Whether the "has_strict_flexible_array_data_member_conversion"
+  // property was set.
+  bool					has_strict_fam_conv_;
 
   priv();
 
@@ -602,7 +605,8 @@  public:
       type_kind_(type_kind),
       consider_reach_kind_(consider_reach_kind),
       reach_kind_(reach_kind),
-      has_size_change_(false)
+      has_size_change_(false),
+      has_strict_fam_conv_(false)
   {}
 
   /// Get the regular expression object associated to the 'type_name_regex'
diff --git a/src/abg-suppression.cc b/src/abg-suppression.cc
index 326d003e..91199629 100644
--- a/src/abg-suppression.cc
+++ b/src/abg-suppression.cc
@@ -808,6 +808,14 @@  void
 type_suppression::set_changed_enumerators_regexp(const vector<regex::regex_t_sptr>& n)
 {priv_->changed_enumerators_regexp_ = n;}
 
+bool
+type_suppression::has_strict_fam_conversion () const
+{return priv_->has_strict_fam_conv_;}
+
+void
+type_suppression::set_has_strict_fam_conversion(bool f)
+{priv_->has_strict_fam_conv_ = f;}
+
 /// Evaluate this suppression specification on a given diff node and
 /// say if the diff node should be suppressed or not.
 ///
@@ -967,6 +975,11 @@  type_suppression::suppresses_diff(const diff* diff) const
   const class_diff* klass_diff = dynamic_cast<const class_diff*>(d);
   if (klass_diff)
     {
+      const class_decl_sptr& first_class =
+	klass_diff->first_class_decl();
+      const class_decl_sptr& second_class =
+	klass_diff->second_class_decl();
+
       // We are looking at a class diff ...
       if (!get_data_member_insertion_ranges().empty())
 	{
@@ -981,9 +994,6 @@  type_suppression::suppresses_diff(const diff* diff) const
 	      // that suppression applies to types that have size
 	      // change.
 
-	      const class_decl_sptr& first_type_decl =
-		klass_diff->first_class_decl();
-
 	      if (klass_diff->inserted_data_members().empty()
 		  && klass_diff->changed_data_members().empty())
 		// So there is a has_data_member_inserted_* clause,
@@ -1001,7 +1011,7 @@  type_suppression::suppresses_diff(const diff* diff) const
 		  for (const auto& range : get_data_member_insertion_ranges())
 		    if (is_data_member_offset_in_range(is_var_decl(member),
 						       range,
-						       first_type_decl.get()))
+						       first_class.get()))
 		      matched = true;
 
 		  if (!matched)
@@ -1017,7 +1027,7 @@  type_suppression::suppresses_diff(const diff* diff) const
 
 		  for (const auto& range : get_data_member_insertion_ranges())
 		    if (is_data_member_offset_in_range(member, range,
-						       first_type_decl.get()))
+						       first_class.get()))
 		      matched = true;
 
 		  if (!matched)
@@ -1027,6 +1037,28 @@  type_suppression::suppresses_diff(const diff* diff) const
 	  else
 	    return false;
 	}
+
+      // Support for the
+      // "has_strict_flexible_array_data_member_conversion = true"
+      // clause.
+      if (has_strict_fam_conversion())
+	{
+	  // Let's detect if the first class of the diff has a fake
+	  // flexible array data member that got turned into a real
+	  // flexible array data member.
+	  if (!(
+		(get_has_size_change())
+		// This situation will always result in a size change,
+		// so check that "has_size_change = true" before
+		// processing further
+		&&
+		(has_fake_flexible_array_data_member(first_class)
+		 && has_flexible_array_data_member(second_class))
+		// A fake flexible array member has been changed into
+		// a real flexible array ...
+		))
+	    return false;
+	}
     }
 
   const enum_diff* enum_dif = dynamic_cast<const enum_diff*>(d);
@@ -2321,6 +2353,14 @@  read_type_suppression(const ini::config::section& section)
       }
     }
 
+  // Support "has_strict_flexible_array_data_member_conversion"
+  ini::simple_property_sptr has_strict_fam_conv =
+    is_simple_property
+    (section.find_property("has_strict_flexible_array_data_member_conversion"));
+  string has_strict_fam_conv_str = has_strict_fam_conv
+    ? has_strict_fam_conv->get_value()->as_string()
+    : "";
+
   if (section.get_name() == "suppress_type")
     result.reset(new type_suppression(label_str, name_regex_str, name_str));
   else if (section.get_name() == "allow_type")
@@ -2388,6 +2428,9 @@  read_type_suppression(const ini::config::section& section)
       && !changed_enumerators_regexp.empty())
     result->set_changed_enumerators_regexp(changed_enumerators_regexp);
 
+  if (has_strict_fam_conv_str == "yes" || has_strict_fam_conv_str == "true")
+    result->set_has_strict_fam_conversion(true);
+
   return result;
 }
 
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
new file mode 100644
index 00000000..5cb8d880
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr
@@ -0,0 +1,4 @@ 
+[suppress_type]
+  type_kind = struct
+  has_size_change = true
+  has_strict_flexible_array_data_member_conversion = true
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
new file mode 100644
index 00000000..384409d0
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr
@@ -0,0 +1,3 @@ 
+[suppress_type]
+  type_kind = struct
+  has_strict_flexible_array_data_member_conversion = true
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
new file mode 100644
index 00000000..b4ea5bf1
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt
@@ -0,0 +1,4 @@ 
+Functions changes summary: 0 Removed, 0 Changed, 0 Added function
+Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
+Unreachable types summary: 0 removed, 0 changed (1 filtered out), 0 added type
+
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
new file mode 100644
index 00000000..2352dd4e
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt
@@ -0,0 +1,14 @@ 
+Functions changes summary: 0 Removed, 0 Changed, 0 Added function
+Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
+Unreachable types summary: 0 removed, 1 changed, 0 added type
+
+1 changed type unreachable from any public interface:
+
+  [C] 'struct foo' changed:
+    type size changed from 64 to 32 (in bits)
+    1 data member change:
+      type of 'int flex[1]' changed:
+        type name changed from 'int[1]' to 'int[]'
+        array type size changed from 32 to 'unknown'
+        array type subrange 1 changed length from 1 to 'unknown'
+
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
new file mode 100644
index 00000000..1397cd52
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.c
@@ -0,0 +1,11 @@ 
+/*
+ * Compile this with:
+ *   gcc -g -c test-has-strict-flexible-array-data-member-conversion-v0.c
+ */
+struct foo
+{
+  int x;
+  int flex[1];
+};
+
+struct foo S;
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o
new file mode 100644
index 0000000000000000000000000000000000000000..8d0a755d353d580e6afb96dc55a021322caf5a93
GIT binary patch
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diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
--- /dev/null
+++ b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.c
@@ -0,0 +1,11 @@ 
+/*
+ * Compile this with:
+ *   gcc -g -c test-has-strict-flexible-array-data-member-conversion-v1.c
+ */
+struct foo
+{
+  int x;
+  int flex[];
+};
+
+struct foo S;
diff --git a/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o b/tests/data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o
new file mode 100644
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GIT binary patch
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diff --git a/tests/test-diff-suppr.cc b/tests/test-diff-suppr.cc
--- a/tests/test-diff-suppr.cc
+++ b/tests/test-diff-suppr.cc
@@ -2376,6 +2376,26 @@  InOutSpec in_out_specs[] =
     "data/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt",
     "output/test-diff-suppr/test-has-data-member-inserted-at-2-report.3.txt"
   },
+  {
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
+    "",
+    "",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-1.suppr",
+    "--drop-private-types --no-default-suppression --non-reachable-types",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
+    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-1.txt",
+  },
+  {
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v0.o",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-v1.o",
+    "",
+    "",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-2.suppr",
+    "--drop-private-types --no-default-suppression --non-reachable-types",
+    "data/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
+    "output/test-diff-suppr/test-has-strict-flexible-array-data-member-conversion-report-2.txt",
+  },
   // This should be the last entry
   {NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL}
 };