Re: [dpdk-dev] [PATCH 2/2] devtools: add path to additional shared object files

[Ruifeng Wang <Ruifeng.Wang@arm.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Wednesday, December 18, 2019 23:32
> To: Laatz, Kevin <kevin.laatz@intel.com>
> Cc: Ruifeng Wang <Ruifeng.Wang@arm.com>; Bruce Richardson
> <bruce.richardson@intel.com>; Aaron Conole <aconole@redhat.com>;
> Michael Santana <maicolgabriel@hotmail.com>; thomas@monjalon.net; Yigit,
> Ferruh <ferruh.yigit@intel.com>; Andrew Rybchenko
> <arybchenko@solarflare.com>; dev <dev@dpdk.org>; Gavin Hu
> <Gavin.Hu@arm.com>; Honnappa Nagarahalli
> <Honnappa.Nagarahalli@arm.com>; nd <nd@arm.com>
> Subject: Re: [dpdk-dev] [PATCH 2/2] devtools: add path to additional shared
> object files
> 
> On Wed, Dec 18, 2019 at 2:43 PM Laatz, Kevin <kevin.laatz@intel.com> wrote:
> >
> > On 18/12/2019 08:23, David Marchand wrote:
> > > On Wed, Dec 18, 2019 at 6:39 AM Ruifeng Wang <ruifeng.wang@arm.com>
> wrote:
> > >> librte_mempool_ring.so and librte_pmd_null.so are in 'drivers' folder.
> > >> Add 'drivers' into LD_LIBRARY_PATH so that testpmd can find and
> > >> make use of these shared libraries.
> > >>
> > >> Signed-off-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > >> Reviewed-by: Gavin Hu <gavin.hu@arm.com>
> > >> ---
> > >>   devtools/test-null.sh | 2 +-
> > >>   1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/devtools/test-null.sh b/devtools/test-null.sh index
> > >> f39af2c06..548de8113 100755
> > >> --- a/devtools/test-null.sh
> > >> +++ b/devtools/test-null.sh
> > >> @@ -20,7 +20,7 @@ if [ ! -f "$testpmd" ] ; then
> > >>   fi
> > >>
> > >>   if ldd $testpmd | grep -q librte_ ; then
> > >> -       export LD_LIBRARY_PATH=$build/lib:$LD_LIBRARY_PATH
> > >> +       export
> > >> + LD_LIBRARY_PATH=$build/drivers:$build/lib:$LD_LIBRARY_PATH
> > >>          libs='-d librte_mempool_ring.so -d librte_pmd_null.so'
> > >>   else
> > >>          libs=
> > >> --
> > >> 2.17.1
> > >>
> > > I'm surprised to see this.
> > > So far, the CI ran fine without it, so something is different in the
> > > environment.
> > >
> > > I can see that the RPATH entry disappeared from the testpmd binary.
> > > Xenial:
> > > # readelf -d build/app/dpdk-testpmd |grep RPATH
> > >   0x000000000000000f (RPATH)              Library rpath:
> > > [$ORIGIN/../lib:$ORIGIN/../drivers:XXXXXXXXXXXXX]
> > >
> > > (not sure what XXXX purpose is, but different topic)
> > >
> > > Bionic:
> > > # readelf -d build/app/dpdk-testpmd |grep RPATH
> >
> > It looks like RPATH just changed to be named RUNPATH in Bionic:
> >
> > # readelf -d build/app/dpdk-testpmd | grep R.*PATH
> >   0x000000000000001d (RUNPATH)            Library runpath:
> > [$ORIGIN/../lib:$ORIGIN/../drivers:XXXXXXXXXXXXX]
> 
> Did some experiment with some test program and .so of mine.
> TL;DR, if I understand correctly, RPATH on the binary applies to all lookups,
> even in a subsequent .so code.
> But RUNPATH only applies to the current ELF, meaning that the dlopen() in
> my intermediate .so does not get it.
> 
> dlopen() is called from librte_eal.so, and RUNPATH on testpmd is not enough.
> 
Thanks for your experiment and analysis. Really happy to know more around the issue.

> 
> Details:
> [dmarchan@dmarchan plop]$ cat main.c
> extern void loader(void);
> 
> int main(int argc, char *argv[])
> {
>     loader();
>     return 0;
> }
> [dmarchan@dmarchan plop]$ cat loader/loader.c #include <dlfcn.h>
> #include <stdio.h>
> 
> void loader(void)
> {
>     if (dlopen("lib.so", RTLD_NOW) == NULL)
>         fprintf(stderr, "%s\n", dlerror()); }
> 
> [dmarchan@dmarchan plop]$ cat lib/lib.c
> #include <stdio.h>
> 
> __attribute__((constructor))
> static void plop(void)
> {
>     fprintf(stdout, "plop\n");
> }
> 
> 
> # no rpath/runpath
> [dmarchan@dmarchan plop]$ gcc -o lib/lib.so -Wall -Werror -shared -fPIC
> lib/lib.c [dmarchan@dmarchan plop]$ gcc -o loader/loader.so -Wall -Werror -
> shared -fPIC loader/loader.c -ldl [dmarchan@dmarchan plop]$ gcc -o main -
> Wall -Werror main.c loader/loader.so [dmarchan@dmarchan plop]$ readelf -
> d main |grep R.*PATH [dmarchan@dmarchan plop]$ ./main
> lib.so: cannot open shared object file: No such file or directory
> 
> # using rpath on final binary
> [dmarchan@dmarchan plop]$ gcc -o main -Wall -Werror main.c
> loader/loader.so -Wl,-rpath,loader:lib [dmarchan@dmarchan plop]$ readelf -
> d main |grep R.*PATH
>  0x000000000000000f (RPATH)              Library rpath: [loader:lib]
> [dmarchan@dmarchan plop]$ ./main
> plop
> 
> # using runpath on final binary
> [dmarchan@dmarchan plop]$ gcc -o main -Wall -Werror main.c
> loader/loader.so -Wl,-enable-new-dtag,-rpath,loader:lib
> [dmarchan@dmarchan plop]$ readelf -d main |grep R.*PATH
>  0x000000000000001d (RUNPATH)            Library runpath: [loader:lib]
> [dmarchan@dmarchan plop]$ ./main
> lib.so: cannot open shared object file: No such file or directory
> 
> # using runpath on loader
> [dmarchan@dmarchan plop]$ gcc -o loader/loader.so -Wall -Werror -shared -
> fPIC loader/loader.c -ldl -Wl,-enable-new-dtag,-rpath,lib
> [dmarchan@dmarchan plop]$ readelf -d loader/loader.so |grep R.*PATH
>  0x000000000000001d (RUNPATH)            Library runpath: [lib]
> [dmarchan@dmarchan plop]$ gcc -o main -Wall -Werror main.c
> loader/loader.so -Wl,-enable-new-dtag,-rpath,loader
> [dmarchan@dmarchan plop]$ readelf -d main |grep R.*PATH
>  0x000000000000001d (RUNPATH)            Library runpath: [loader]
> [dmarchan@dmarchan plop]$ ./main
> plop
> 
> 
> > > Adding Bruce and Kevin, as I think this is the same issue than:
> > > http://mails.dpdk.org/archives/dev/2019-December/153627.html
> > > Could it be a change in meson?
> >
> > Yes, looks like the same error to me.
> >
> > I'm not sure this is solely a meson issue, I often need to pass -d
> > librte_mempool_ring.so when using make builds too. Maybe I'm missing
> > something here?
> 
> In a make build directory, all libraries ends up in the same lib/ directory and
> the test-null.sh script work with the current LD_LIBRARY_PATH.
> 
> 
> Ruifeng patch seems valid to me, but I would love some explanations in the
> commitlog.
> 
Sure. I will re-spin to add explanations.

> --
> David Marchand