Re: [RFC] elf: Implement filtering of symbols historically defined in libpthread

["H.J. Lu via Libc-alpha" <libc-alpha@sourceware.org>]

On Tue, May 4, 2021 at 5:04 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * H. J. Lu:
>
> > Since we want to detect the binaries which were linked against glibc
> > older than 2.34, we should use the glibc version to check the old
> > binaries.
>
> The patch attempts to detect old main programs by looking for the
> GLIBC_2.34 symbol version.  Since we added __libc_start_main@GLIBC_2.34
> (which is called from our version of _start), all standard main programs
> linked with glibc 2.34 or later will have this symbol version.
>
> > Of course, we should make a complete list of functions which are
> > really implemented in libpthread.so and will be moved to libc.so in
> > glibc 2.34.
>
> I'm not sure if it is necessary to do this for *all* symbols.  Formally,
> a symbol added after glibc 2.0 is not suitable for detecting the
> potential multi-threaded nature of a process because the application
> could be built for an earlier glibc version, where the symbol is not
> available, but pthread_create can still create new threads.  The use of
> pthread_mutexattr_gettype@@GLIBC_2.1 as the detection symbol does not
> follow the rule, of course.  With the explicit table approach (as in the
> patch), we can add additional lookup symbols later, so I think we can
> start out with the GLIBC_2.0 and GLIBC_2.1 symbols plus thrd_exit (the
> latter is also used by gnulib for some reason).
>

Can we invent a symbol or version to detect the older binaries?
If not, can GNU property, ABI note, .... help here?

-- 
H.J.