Re: [PATCH] tests: Add -ldl to dwfl_proc_attach_LDFLAGS

["Dmitry V. Levin" <ldv@altlinux.org>]

On Thu, Nov 18, 2021 at 10:23:41PM +0100, Mark Wielaard wrote:
> dwfl-proc-attach uses (overrides) dlopen (so it does nothing).  This
> seems to cause a versioned dlopen symbol to be pulled in when building
> with LTO. Resulting in a link failure (when dlopen isn't integrated
> into libc):
> 
> /usr/bin/ld: dwfl-proc-attach.o (symbol from plugin): undefined
> reference to symbol 'dlopen@@GLIBC_2.2.5'
> /usr/bin/ld: /usr/lib64/libdl.so.2: error adding symbols: DSO missing
> from command line collect2: error: ld returned 1 exit status
> 
> So simply explicitly add -ldl to the LDFLAGS.
> 
> Signed-off-by: Mark Wielaard <mark@klomp.org>
> ---
>  tests/ChangeLog   | 4 ++++
>  tests/Makefile.am | 2 +-
>  2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/tests/ChangeLog b/tests/ChangeLog
> index a59cdd51..97cb3fa3 100644
> --- a/tests/ChangeLog
> +++ b/tests/ChangeLog
> @@ -1,3 +1,7 @@
> +2021-11-18  Mark Wielaard  <mark@klomp.org>
> +
> +	* Makefile.am (dwfl_proc_attach_LDFLAGS): Add -ldl.
> +
>  2021-11-05  Frank Ch. Eigler  <fche@redhat.com>
>  
>  	PR28430
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index bfb8b13a..f212f9fb 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -717,7 +717,7 @@ strptr_LDADD = $(libelf)
>  newdata_LDADD = $(libelf)
>  elfstrtab_LDADD = $(libelf)
>  dwfl_proc_attach_LDADD = $(libdw)
> -dwfl_proc_attach_LDFLAGS = -pthread $(AM_LDFLAGS)
> +dwfl_proc_attach_LDFLAGS = -pthread -ldl $(AM_LDFLAGS)

Let's make clear what's going on here.  First of all, dwfl-proc-attach.c
does not use dlopen so it doesn't pull it in and doesn't need -ldl.
In regular builds, dwfl-proc-attach.o is linked with ../libdw/libdw.so
which in turn uses dlopen and is already linked with -ldl.
When elfutils is configured with --enable-gprof or --enable-gcov,
BUILD_STATIC is enabled and dwfl-proc-attach.o is linked with
../libdw/libdw.a -lz $(zip_LIBS) $(libelf) $(libebl) -ldl -lpthread
which already contains -ldl.
In any case, I fail to understand why dwfl-proc-attach might need
an extra -ldl, especially in LDFLAGS which goes before LDADD
in the linking command.


-- 
ldv