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SubjectRe: [PATCH 5.8 35/99] tools/libbpf: Avoid counting local symbols in ABI check
[adding Michael Ellerman, linux-ppc maintainer]

Hello Justin,

On Tue, 29 Sep 2020 at 14:54, Justin Forbes <jmforbes@linuxtx.org> wrote:
>
> On Tue, Sep 29, 2020 at 6:53 AM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > From: Tony Ambardar <tony.ambardar@gmail.com>
> >
> > [ 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@gmail.com>
> > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > Acked-by: Andrii Nakryiko <andriin@fb.com>
> > Link: https://lore.kernel.org/bpf/20200905214831.1565465-1-Tony.Ambardar@gmail.com
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
>
> 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 \
> >
> >

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