Bug 28664 - misinterpretation of default template instantiation naming idioms.
Summary: misinterpretation of default template instantiation naming idioms.
Status: NEW
Alias: None
Product: libabigail
Classification: Unclassified
Component: default (show other bugs)
Version: unspecified
: P2 normal
Target Milestone: ---
Assignee: Dodji Seketeli
URL:
Keywords:
Depends on:
Blocks: 27019
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Reported: 2021-12-07 00:50 UTC by Ben Woodard
Modified: 2021-12-07 00:53 UTC (History)
1 user (show)

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Description Ben Woodard 2021-12-07 00:50:26 UTC 
When comparing gcc compiled libabigail.so.0.0.0 to to the clang compiled version one commonly reported error is something like this:

  [C] 'function void abigail::comparison::apply_filters(abigail::comparison::corpus_diff_sptr)' has some indirect sub-type changes:
    parameter 1 of type 'typedef abigail::comparison::corpus_diff_sptr' has sub-type changes:
      underlying type 'class std::shared_ptr<abigail::comparison::corpus_diff>' at shared_ptr.h:122:1 changed:
        type size hasn't changed
        1 base class deletion:
          class std::__shared_ptr<abigail::comparison::corpus_diff, (__gnu_cxx::_Lock_policy)2> at shared_ptr_base.h:1052:1
        1 base class insertion:
          class std::__shared_ptr<abigail::comparison::corpus_diff, __gnu_cxx::_S_atomic> at shared_ptr_base.h:1052:1

$ abidiff g5/lib/libabigail.so.0.0.0 l5/lib/libabigail.so.0.0.0 

the gcc object can be found: http://ssh.bencoyote.net/~ben/libabigail.so.0.0.0.gcc.bz2 while the clang object can be found: https://sourceware.org/bugzilla/attachment.cgi?id=13812

This seems to be a case where libabigail is optimizing the comparison a bit too much by using the textual representative of the template value parameter rather than following down into the type.

In the GCC DWARF you see:

 [5673ec]      class_type           abbrev: 75
               name                 (strp) "__shared_ptr<abigail::comparison::corpus_diff, (__gnu_cxx::_Lock_policy)2>"
               byte_size            (data1) 16
               decl_file            (data1) shared_ptr_base.h (3)
               decl_line            (data2) 1052
               decl_column          (data1) 11
               sibling              (ref4) [567686]
 [5673fa]        inheritance          abbrev: 56
                 type                 (ref4) [567333]
                 data_member_location (implicit_const) 0
                 accessibility        (data1) public (1)
...
 [56767b]        template_value_parameter abbrev: 58
                 name                 (string) "_Lp"
                 type                 (ref4) [5ca886]
                 const_value          (data1) 2

 [5ca886]      enumeration_type     abbrev: 239
               name                 (strp) "_Lock_policy"
               encoding             (data1) unsigned (7)
               byte_size            (implicit_const) 4
               type                 (ref4) [51049d]
               decl_file            (data1) concurrence.h (83)
               decl_line            (data1) 49
               decl_column          (implicit_const) 8
               sibling              (ref4) [5ca8aa]
 [5ca897]        enumerator           abbrev: 108
                 name                 (strp) "_S_single"
                 const_value          (data1) 0
 [5ca89d]        enumerator           abbrev: 108
                 name                 (strp) "_S_mutex"
                 const_value          (data1) 1
 [5ca8a3]        enumerator           abbrev: 108
                 name                 (strp) "_S_atomic"
                 const_value          (data1) 2

While clang emits:

 [3037c0]      class_type           abbrev: 14
               calling_convention   (data1) pass_by_reference (4)
               name                 (strx2) "__shared_ptr<abigail::comparison::corpus_diff, __gnu_cxx::_S_atomic>"
               byte_size            (data1) 16
               decl_file            (data1) shared_ptr_base.h (28)
               decl_line            (data2) 1052
 [3037c8]        template_type_parameter abbrev: 15
                 type                 (ref4) [384ce8]
                 name                 (strx1) "_Tp"
 [3037ce]        template_value_parameter abbrev: 92
                 type                 (ref4) [37737f]
                 name                 (strx2) "_Lp"
                 default_value        (flag_present) yes
                 const_value          (sdata) 2 (2)
...
[37737f]      enumeration_type     abbrev: 175
               type                 (ref4) [384331]
               name                 (strx1) "_Lock_policy"
               byte_size            (data1) 4
               decl_file            (data1) concurrence.h (3)
               decl_line            (data1) 49
 [377389]        enumerator           abbrev: 176
                 name                 (strx1) "_S_single"
                 const_value          (udata) 0
 [37738d]        enumerator           abbrev: 176
                 name                 (strx1) "_S_mutex"
                 const_value          (udata) 1
 [377391]        enumerator           abbrev: 176
                 name                 (strx1) "_S_atomic"
                 const_value          (udata) 2

It looks to me like libabigail is relying on the class name when comparing the template instantiation rather than actually comparing the template value parameters. This confuses libabigail into believing the template instantiation is difference when it is in fact the same.