Re: [PATCH] ld.so: Support moving versioned symbols between sonames [BZ #24741]

[Yann Droneaud <ydroneaud at opteya dot com>]

Hi,

Le jeudi 27 juin 2019 à 19:13 +0200, Florian Weimer a écrit :
> * Yann Droneaud:
> 
> > > diff --git a/elf/Makefile b/elf/Makefile
> > > index 27a2fa8c14..76b0565054 100644
> > > --- a/elf/Makefile
> > > +++ b/elf/Makefile
> > > @@ -191,7 +191,8 @@ tests += restest1 preloadtest loadfail multiload origtest resolvfail \
> > >  	 tst-nodelete2 tst-audit11 tst-audit12 tst-dlsym-error tst-noload \
> > >  	 tst-latepthread tst-tls-manydynamic tst-nodelete-dlclose \
> > >  	 tst-debug1 tst-main1 tst-absolute-sym tst-absolute-zero tst-big-note \
> > > -	 tst-unwind-ctor tst-unwind-main tst-audit13
> > > +	 tst-unwind-ctor tst-unwind-main tst-audit13 \
> > > +	 tst-sonamemove tst-sonamemove-dlopen
> > 
> > tst-sonamemove could be name tst-sonamemove-link to make obvious the
> > difference with -dlopen.
> 
> Good idea.
> 
> > > +$(objpfx)tst-sonamemove-dlopen: $(libdl)
> > > +$(objpfx)tst-sonamemove.out: \
> > > +  $(objpfx)tst-sonamemove-runmod1.so \
> > > +  $(objpfx)tst-sonamemove-runmod2.so
> > > +
> > 
> > The last three lines duplicate those above.
> 
> Fixed.
> 
> > > +/* moved_function is linked against tst-sonamemove-runmod1.so, but the
> > > +   actual implementation is in tst-sonamemove-runmod1.so. */
> > 
> > I found this comment unclear. tst-sonamemove is linked against tst-
> > sonamemove-linkmod1.so, which has tst-sonamemove-runmod1.so soname.
> > When tst-sonamemove is run, tst-sonamemove-runmod1.so is loaded, which
> > imply loading tst-sonamemove-runmod2.so as a dependency. tst-
> > sonamemove-runmod2.so is where move_function's implementation is.
> 
> I tried to explain this more explictly:
> 
> /* At link time, moved_function is bound to the symbol version
>    SONAME_MOVE in tst-sonamemove-runmod1.so, using the
>    tst-sonamemove-linkmod1.so stub object.
> 
>    At run time, the process loads the real tst-sonamemove-runmod1.so,
>    which depends on tst-sonamemove-runmod2.so.
>    tst-sonamemove-runmod1.so does not define moved_function, but
>    tst-sonamemove-runmod2.so does.
> 
>    The net effect is that the versioned symbol
>    moved_function@SONAME_MOVE moved from the soname
>    tst-sonamemove-linkmod1.so at link time to the soname
>    tst-sonamemove-linkmod2.so at run time. */
> 

Thanks.

LGTM.

Reviewed-by: Yann Droneaud <ydroneaud@opteya.com>

Regards.

-- 
Yann Droneaud
OPTEYA