On Mon, 2019-03-25 at 10:45 +0800, Ye Xiaolong wrote:
> On 03/24, Luca Boccassi wrote:
> > On Sun, 2019-03-17 at 11:34 +0800, Ye Xiaolong wrote:
> > > On 03/02, Ye Xiaolong wrote:
> > > > > > _LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_AF_PACKET) +=
> > > > > > -lrte_pmd_af_packet
> > > > > > +_LDLIBS-$(CONFIG_RTE_LIBRTE_PMD_AF_XDP) +=
> > > > > > -lrte_pmd_af_xdp
> > > > > > -lelf -lbpf
> > > > >
> > > > > Are symbols from libelf being used by the PMD?
> > > >
> > > > Hmm, it is a leftover of RFC, libelf is no longer needed in
> > > > this
> > > > version, will
> > > > remove it in next version.
> > > >
> > >
> > > Correction, libelf is needed for libbpf, so we still need to keep
> > > it.
> >
> > If libbpf needs libelf for its internal usage, it should be linked
> > against it itself. Unless symbols from libelf are used in static
> > functions defined in libbpf's public headers. Is this the case?
> >
>
> Yes, that's the case. without the libelf, it would have build error
> as below,
> and these symbols are used in static functions of libbpf.
>
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_nextscn'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_rawdata'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_memory'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `gelf_getrel'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_strptr'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_end'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_getscn'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_begin'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `gelf_getsym'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_version'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `gelf_getehdr'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `elf_getdata'
> /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../lib64/libbpf.so:
> undefined reference to `gelf_getshdr'
>
> Thanks,
> Xiaolong
Looking at that list, at least the very first symbol is not used by a
public header, but internally in libbpf:
$ grep -r elf_nextscn
libbpf.c: while ((scn = elf_nextscn(elf, scn)) != NULL) {
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/lib/bpf/libbpf.c#n793
None of those symbols are used from the public headers:
$ grep elf_ bpf.h libbpf.h btf.h
$
Therefore, this is an omission in libbpf's Makefile, as it must link
against libelf. Please raise a ticket or send a patch upstream, and
remove the -lelf from DPDK's makefiles.
--
Kind regards,
Luca Boccassi
