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From: "woodard at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: libabigail@sourceware.org
Subject: [Bug default/27208] New: abicompat doesn't check back calls.
Date: Tue, 19 Jan 2021 21:54:31 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D27208

            Bug ID: 27208
           Summary: abicompat doesn't check back calls.
           Product: libabigail
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: default
          Assignee: dodji at redhat dot com
          Reporter: woodard at redhat dot com
                CC: libabigail at sourceware dot org
  Target Milestone: ---

Created attachment 13135
  --> https://sourceware.org/bugzilla/attachment.cgi?id=3D13135&action=3Ded=
it
reproducer code.

abicompat doesn't check calls from a library into functions provided by an
application. It only checks that calls from the app into a library provide =
the
same ABI. This is not sufficient to assert abi compatibility.

Say for example you have:

#include <stdio.h>

char *backcall( char *arg){
  return arg+1;
}

char *libcall( char *arg);

int main(int argc, char **argv){
  printf("%s\n", libcall(argv[0]));
  return 0;
}

and in a library you have:

// this would normally be in a header provided by the app
// it is just here to make the reproducer simple.
char *backcall( char *arg);=20

char *libcall( char *arg){
  return backcall(arg);
}

However an older or a newer version of the app provided a different interfa=
ce
and so the library is:

// notice this is different
int backcall( char *arg);

char *libcall( char *arg){
  return arg+backcall(arg);
}

So abicompat should point out that the second version of the library is not
compatible with the app but it doesn't.

$ abicompat app1 libt1.so libt2.so=20
$ echo $?
0

The problem is that abicompat doesn't perform 2 way comparison with the
library. it doesn't mark the call from the library to the application as ne=
eded
then compare that to what the application provides.

This programming style is not uncommon. It happens anytime there is a defin=
ed
plugin interface

--=20
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