[Bug 272474] lib/libc: bcmp may give wrong results on LP64 systems

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=272474

            Bug ID: 272474
           Summary: lib/libc: bcmp may give wrong results on LP64 systems
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: fuz@FreeBSD.org
             Flags: mfc-stable13?, mfc-stable12?

Created attachment 243358
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=243358&action=edit
fix bcmp() bug

bcmp() returns the number of remaining bytes when the main loop exits.
In case of a match, this is zero, else a positive integer.  On systems
where SIZE_MAX > INT_MAX, the implicit conversion from size_t to int in
the return value may cause the number of remaining bytes to overflow,
becoming zero and falsely indicating a successful comparison.

This bug affects any 64 bit system that doesn't have a machdep implementation
of bcmp().  This should be all except amd64.  OpenBSD has the same
implementation and is likely affected, too.  The bug has presumably been
present since ancient times.

The attached patch fixes the bug by always returning 0 on equality, 1
otherwise.

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