Re: [PATCH 5.8 35/99] tools/libbpf: Avoid counting local symbols in ABI check

[Tony Ambardar]

[adding Michael Ellerman, linux-ppc maintainer]

Hello Justin,

On Tue, 29 Sep 2020 at 14:54, Justin Forbes <jmforbes@xxxxxxxxxxx> wrote:
>
> On Tue, Sep 29, 2020 at 6:53 AM Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> >
> > From: Tony Ambardar <tony.ambardar@xxxxxxxxx>
> >
> > [ Upstream commit 746f534a4809e07f427f7d13d10f3a6a9641e5c3 ]
> >
> > Encountered the following failure building libbpf from kernel 5.8.5 sources
> > with GCC 8.4.0 and binutils 2.34: (long paths shortened)
> >
> >   Warning: Num of global symbols in sharedobjs/libbpf-in.o (234) does NOT
> >   match with num of versioned symbols in libbpf.so (236). Please make sure
> >   all LIBBPF_API symbols are versioned in libbpf.map.
> > #  --- libbpf_global_syms.tmp    2020-09-02 07:30:58.920084380 +0000
> > #  +++ libbpf_versioned_syms.tmp 2020-09-02 07:30:58.924084388 +0000
> >   @@ -1,3 +1,5 @@
> >   +_fini
> >   +_init
> >    bpf_btf_get_fd_by_id
> >    bpf_btf_get_next_id
> >    bpf_create_map
> >   make[4]: *** [Makefile:210: check_abi] Error 1
> >
> > Investigation shows _fini and _init are actually local symbols counted
> > amongst global ones:
> >
> >   $ readelf --dyn-syms --wide libbpf.so|head -10
> >
> >   Symbol table '.dynsym' contains 343 entries:
> >      Num:    Value  Size Type    Bind   Vis      Ndx Name
> >        0: 00000000     0 NOTYPE  LOCAL  DEFAULT  UND
> >        1: 00004098     0 SECTION LOCAL  DEFAULT   11
> >        2: 00004098     8 FUNC    LOCAL  DEFAULT   11 _init@@LIBBPF_0.0.1
> >        3: 00023040     8 FUNC    LOCAL  DEFAULT   14 _fini@@LIBBPF_0.0.1
> >        4: 00000000     0 OBJECT  GLOBAL DEFAULT  ABS LIBBPF_0.0.4
> >        5: 00000000     0 OBJECT  GLOBAL DEFAULT  ABS LIBBPF_0.0.1
> >        6: 0000ffa4     8 FUNC    GLOBAL DEFAULT   12 bpf_object__find_map_by_offset@@LIBBPF_0.0.1
> >
> > A previous commit filtered global symbols in sharedobjs/libbpf-in.o. Do the
> > same with the libbpf.so DSO for consistent comparison.
> >
> > Fixes: 306b267cb3c4 ("libbpf: Verify versioned symbols")
> > Signed-off-by: Tony Ambardar <Tony.Ambardar@xxxxxxxxx>
> > Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> > Acked-by: Andrii Nakryiko <andriin@xxxxxx>
> > Link: https://lore.kernel.org/bpf/20200905214831.1565465-1-Tony.Ambardar@xxxxxxxxx
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> This seems to work everywhere else, but breaks PPC64LE.
>

I also ran into a PPC build error while working on some bpf problems,
but it seemed
like a pre-existing PPC issue. I did submit an upstream fix, which is
marked for stable
and being reviewed by Michael. See here for discussion and the patch:
https://lkml.org/lkml/2020/9/17/668.

Is that the same problem you encountered? Does that patch address your issue?

Thanks,
Tony

> Justin
>
> > ---
> >  tools/lib/bpf/Makefile |    2 ++
> >  1 file changed, 2 insertions(+)
> >
> > --- a/tools/lib/bpf/Makefile
> > +++ b/tools/lib/bpf/Makefile
> > @@ -152,6 +152,7 @@ GLOBAL_SYM_COUNT = $(shell readelf -s --
> >                            awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}' | \
> >                            sort -u | wc -l)
> >  VERSIONED_SYM_COUNT = $(shell readelf --dyn-syms --wide $(OUTPUT)libbpf.so | \
> > +                             awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}' | \
> >                               grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 | sort -u | wc -l)
> >
> >  CMD_TARGETS = $(LIB_TARGET) $(PC_FILE)
> > @@ -219,6 +220,7 @@ check_abi: $(OUTPUT)libbpf.so
> >                     awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}'|  \
> >                     sort -u > $(OUTPUT)libbpf_global_syms.tmp;           \
> >                 readelf --dyn-syms --wide $(OUTPUT)libbpf.so |           \
> > +                   awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}'|  \
> >                     grep -Eo '[^ ]+@LIBBPF_' | cut -d@ -f1 |             \
> >                     sort -u > $(OUTPUT)libbpf_versioned_syms.tmp;        \
> >                 diff -u $(OUTPUT)libbpf_global_syms.tmp                  \
> >
> >