netdev - [PATCH bpf v1] tools/libbpf: avoid counting local symbols in ABI check

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Message-Id: <20200905214831.1565465-1-Tony.Ambardar@gmail.com>
Date:   Sat,  5 Sep 2020 14:48:31 -0700
From:   Tony Ambardar <tony.ambardar@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     Tony Ambardar <Tony.Ambardar@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrey Ignatov <rdna@...com>
Subject: [PATCH bpf v1] tools/libbpf: avoid counting local symbols in ABI check

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@...il.com>
---
 tools/lib/bpf/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index b78484e7a608..9ae8f4ef0aac 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -152,6 +152,7 @@ GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN_SHARED) | \
 			   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 '[^ ]+@...BPF_' | 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 '[^ ]+@...BPF_' | cut -d@ -f1 |		 \
 		    sort -u > $(OUTPUT)libbpf_versioned_syms.tmp; 	 \
 		diff -u $(OUTPUT)libbpf_global_syms.tmp			 \
-- 
2.25.1