abicompat

abicompat checks that an application that links against a given shared library is still ABI compatible with a subsequent version of that library. If the new version of the library introduces an ABI incompatibility, then abicompat hints the user at what exactly that incompatibility is.

Invocation

abicompat [options] [<application> <shared-library-first-version> <shared-library-second-version>]

Options

• --help

  Display a short help about the command and exit.

• --list-undefined-symbols | -u

  Display the list of undefined symbols of the application and exit.

• --show-base-names | -b

  In the resulting report emitted by the tool, this option makes the application and libraries be referred to by their base names only; not by a full absolute name. This can be useful for use in scripts that wants to compare names of the application and libraries independently of what their directory names are.

• --app-debug-info-dir <path-to-app-debug-info-directory>

  Set the path to the directory under which the debug information of the application is supposed to be laid out. This is useful for application binaries for which the debug info is in a separate set of files.

• --lib-debug-info-dir1 <path-to-lib1-debug-info>

  Set the path to the directory under which the debug information of the first version of the shared library is supposed to be laid out. This is useful for shared library binaries for which the debug info is in a separate set of files.

• --lib-debug-info-dir2 <path-to-lib1-debug-info>

  Set the path to the directory under which the debug information of the second version of the shared library is supposed to be laid out. This is useful for shared library binaries for which the debug info is in a separate set of files.

• --weak-mode

  This triggers the weak mode of abicompat. In this mode, only one version of the library is required. That is, abicompat is invoked like this:

  abicompat --weak-mode <the-application> <the-library>
  

  Note that the --weak-mode option can even be omitted if only one version of the library is given, along with the application; in that case, abicompat automatically switches to operate in weak mode:

  abicompat <the-application> <the-library>
  

  In this weak mode, the types of functions and variables exported by the library and consumed by the application (as in, the symbols of the these functions and variables are undefined in the application and are defined and exported by the library) are compared to the version of these types as expected by the application. And if these two versions of types are different, abicompat tells the user what the differences are.

  In other words, in this mode, abicompat checks that the types of the functions and variables exported by the library mean the same thing as what the application expects, as far as the ABI is concerned.

  Note that in this mode, abicompat doesn’t detect exported functions or variables (symbols) that are expected by the application but that are removed from the library. That is why it is called weak mode.

Return values

The exit code of the abicompat command is either 0 if the ABI of the binaries being compared are equal, or non-zero if they differ or if the tool encountered an error.

In the later case, the exit code is a 8-bits-wide bit field in which each bit has a specific meaning.

The first bit, of value 1, named ABIDIFF_ERROR means there was an error.

The second bit, of value 2, named ABIDIFF_USAGE_ERROR means there was an error in the way the user invoked the tool. It might be set, for instance, if the user invoked the tool with an unknown command line switch, with a wrong number or argument, etc. If this bit is set, then the ABIDIFF_ERROR bit must be set as well.

The third bit, of value 4, named ABIDIFF_ABI_CHANGE means the ABI of the binaries being compared are different.

The fourth bit, of value 8, named ABIDIFF_ABI_INCOMPATIBLE_CHANGE means the ABI of the binaries compared are different in an incompatible way. If this bit is set, then the ABIDIFF_ABI_CHANGE bit must be set as well. If the ABIDIFF_ABI_CHANGE is set and the ABIDIFF_INCOMPATIBLE_CHANGE is NOT set, then it means that the ABIs being compared might or might not be compatible. In that case, a human being needs to review the ABI changes to decide if they are compatible or not.

The remaining bits are not used for the moment.

Usage examples

• Detecting a possible ABI incompatibility in a new shared library version:

  $ cat -n test0.h
       1  struct foo
       2  {
       3    int m0;
       4
       5    foo()
       6      : m0()
       7    {}
       8  };
       9
      10  foo*
      11  first_func();
      12
      13  void
      14  second_func(foo&);
      15
      16  void
      17  third_func();
  $
  
  $ cat -n test-app.cc
       1  // Compile with:
       2  //  g++ -g -Wall -o test-app -L. -ltest-0 test-app.cc
       3
       4  #include "test0.h"
       5
       6  int
       7  main()
       8  {
       9    foo* f = first_func();
      10    second_func(*f);
      11    return 0;
      12  }
  $
  
  $ cat -n test0.cc
       1  // Compile this with:
       2  //  g++ -g -Wall -shared -o libtest-0.so test0.cc
       3
       4  #include "test0.h"
       5
       6  foo*
       7  first_func()
       8  {
       9    foo* f = new foo();
      10    return f;
      11  }
      12
      13  void
      14  second_func(foo&)
      15  {
      16  }
      17
      18  void
      19  third_func()
      20  {
      21  }
  $
  
  $ cat -n test1.h
       1  struct foo
       2  {
       3    int  m0;
       4    char m1; /* <-- a new member got added here! */
       5
       6    foo()
       7    : m0(),
       8      m1()
       9    {}
      10  };
      11
      12  foo*
      13  first_func();
      14
      15  void
      16  second_func(foo&);
      17
      18  void
      19  third_func();
  $
  
  $ cat -n test1.cc
       1  // Compile this with:
       2  //  g++ -g -Wall -shared -o libtest-1.so test1.cc
       3
       4  #include "test1.h"
       5
       6  foo*
       7  first_func()
       8  {
       9    foo* f = new foo();
      10    return f;
      11  }
      12
      13  void
      14  second_func(foo&)
      15  {
      16  }
      17
      18  /* Let's comment out the definition of third_func()
      19     void
      20     third_func()
      21     {
      22     }
      23  */
  $
  

  • Compile the first and second versions of the libraries: libtest-0.so and libtest-1.so:

    $ g++ -g -Wall -shared -o libtest-0.so test0.cc
    $ g++ -g -Wall -shared -o libtest-1.so test1.cc
    

  • Compile the application and link it against the first version of the library, creating the test-app binary:

    $ g++ -g -Wall -o test-app -L. -ltest-0.so test-app.cc
    

  • Now, use abicompat to see if libtest-1.so is ABI compatible with app, with respect to the ABI of libtest-0.so:

    $ abicompat test-app libtest-0.so libtest-1.so
    ELF file 'test-app' might not be ABI compatible with 'libtest-1.so' due to differences with 'libtest-0.so' below:
    Functions changes summary: 0 Removed, 2 Changed, 0 Added functions
    Variables changes summary: 0 Removed, 0 Changed, 0 Added variable
    
    2 functions with some indirect sub-type change:
    
      [C]'function foo* first_func()' has some indirect sub-type changes:
        return type changed:
          in pointed to type 'struct foo':
            size changed from 32 to 64 bits
            1 data member insertion:
              'char foo::m1', at offset 32 (in bits)
      [C]'function void second_func(foo&)' has some indirect sub-type changes:
        parameter 0 of type 'foo&' has sub-type changes:
          referenced type 'struct foo' changed, as reported earlier
    
    $
    

  • Now use the weak mode of abicompat, that is, providing just the application and the new version of the library:

    $ abicompat --weak-mode test-app libtest-1.so
    functions defined in library
        'libtest-1.so'
    have sub-types that are different from what application
        'test-app'
    expects:
    
      function foo* first_func():
        return type changed:
          in pointed to type 'struct foo':
            size changed from 32 to 64 bits
            1 data member insertion:
              'char foo::m1', at offset 32 (in bits)
    
    $