Re: RTLD_DEEPBIND question

On Thu, Apr 24, 2025 at 08:56:44AM +0300, Andriy Gapon wrote:
> On 23/04/2025 21:56, Andriy Gapon wrote:
> > BTW, I've been wondering how illumos avoids the problem even though they
> > do not use any special dlopen flags.
> > It turns out that they link almost all system shared libraries with
> > -Bdirect option (which is Solaris/illumos specific).
> > It's somewhat similar to, but different from, -Bsymbolic.
> > https://docs.oracle.com/cd/E23824_01/html/819-0690/aehzq.html#scrolltoc
> > https://docs.oracle.com/cd/E36784_01/html/E36857/gejfe.html
> 
> Oh, and it looks like there is an even better explanation for illumos.
> There is a version map file for libdtrace which explicitly lists API
> functions and makes everything else local.
> https://github.com/illumos/illumos-gate/blob/master/usr/src/lib/libdtrace/common/mapfile-vers
> 
> I wonder why we didn't do the same when porting.
> Maybe we should do that now?

I don't have any objection, but I believe adding a version map after the
fact doesn't accomplish much, assuming that we care deeply about ABI
stability in libdtrace.so (I'm not sure we do though).

> > I think that on FreeBSD we should use symbol visibility attributes or a
> > symbol map to hide (make local) symbols that are not expected to be
> > interposed or have a high chance to be interposed by accident.
> > 
> > IMO, yyparse should definitely get that treatment.
> > 
> > I think that approach would be better than magic rtld tricks.
> > Especially because the tricks do not work with the current rtld.
> > I'd rather make a change to libdtrace.so than to rtld.
> 
> This, while not as nice as the illumos solution, fixes my specific issue:
> diff --git a/cddl/lib/libdtrace/Makefile b/cddl/lib/libdtrace/Makefile
> index d086fffb07bc..58054d129b49 100644
> --- a/cddl/lib/libdtrace/Makefile
> +++ b/cddl/lib/libdtrace/Makefile
> @@ -146,7 +146,8 @@ CFLAGS+=    -fsanitize=address -fsanitize=undefined
>  LDFLAGS+=      -fsanitize=address -fsanitize=undefined
>  .endif
> 
> -LIBADD=        ctf elf proc pthread rtld_db xo
> +VERSION_MAP=   ${.CURDIR}/Symbol.map
> +LIBADD=                ctf elf proc pthread rtld_db xo
> 
>  CLEANFILES=    dt_errtags.c dt_names.c
> 
> diff --git a/cddl/lib/libdtrace/Symbol.map b/cddl/lib/libdtrace/Symbol.map
> new file mode 100644
> index 000000000000..89ee9de65209
> --- /dev/null
> +++ b/cddl/lib/libdtrace/Symbol.map
> @@ -0,0 +1,4 @@
> +{
> +       local:
> +               yy*;
> +};

This just gives the lexer/parser symbols in libdtrace.so local
visibility?  I think that's fine.