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Subject[PATCH 5.8 35/99] tools/libbpf: Avoid counting local symbols in ABI check
Date
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>
---
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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