linux-kernel - [PATCH AUTOSEL 5.16 032/109] libbpf: Fix build issue with llvm-readelf

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Date:   Fri,  1 Apr 2022 10:31:39 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Yonghong Song <yhs@...com>, Delyan Kratunov <delyank@...com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Sasha Levin <sashal@...nel.org>, ast@...nel.org,
        daniel@...earbox.net, nathan@...nel.org, ndesaulniers@...gle.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org, llvm@...ts.linux.dev
Subject: [PATCH AUTOSEL 5.16 032/109] libbpf: Fix build issue with llvm-readelf

From: Yonghong Song <yhs@...com>

[ Upstream commit 0908a66ad1124c1634c33847ac662106f7f2c198 ]

There are cases where clang compiler is packaged in a way
readelf is a symbolic link to llvm-readelf. In such cases,
llvm-readelf will be used instead of default binutils readelf,
and the following error will appear during libbpf build:

  Warning: Num of global symbols in
   /home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/build/libbpf/sharedobjs/libbpf-in.o (367)
   does NOT match with num of versioned symbols in
   /home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/build/libbpf/libbpf.so libbpf.map (383).
   Please make sure all LIBBPF_API symbols are versioned in libbpf.map.
  --- /home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/build/libbpf/libbpf_global_syms.tmp ...
  +++ /home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/build/libbpf/libbpf_versioned_syms.tmp ...
  @@ -324,6 +324,22 @@
   btf__str_by_offset
   btf__type_by_id
   btf__type_cnt
  +LIBBPF_0.0.1
  +LIBBPF_0.0.2
  +LIBBPF_0.0.3
  +LIBBPF_0.0.4
  +LIBBPF_0.0.5
  +LIBBPF_0.0.6
  +LIBBPF_0.0.7
  +LIBBPF_0.0.8
  +LIBBPF_0.0.9
  +LIBBPF_0.1.0
  +LIBBPF_0.2.0
  +LIBBPF_0.3.0
  +LIBBPF_0.4.0
  +LIBBPF_0.5.0
  +LIBBPF_0.6.0
  +LIBBPF_0.7.0
   libbpf_attach_type_by_name
   libbpf_find_kernel_btf
   libbpf_find_vmlinux_btf_id
  make[2]: *** [Makefile:184: check_abi] Error 1
  make[1]: *** [Makefile:140: all] Error 2

The above failure is due to different printouts for some ABS
versioned symbols. For example, with the same libbpf.so,
  $ /bin/readelf --dyn-syms --wide tools/lib/bpf/libbpf.so | grep "LIBBPF" | grep ABS
     134: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LIBBPF_0.5.0
     202: 0000000000000000     0 OBJECT  GLOBAL DEFAULT  ABS LIBBPF_0.6.0
     ...
  $ /opt/llvm/bin/readelf --dyn-syms --wide tools/lib/bpf/libbpf.so | grep "LIBBPF" | grep ABS
     134: 0000000000000000     0 OBJECT  GLOBAL DEFAULT   ABS LIBBPF_0.5.0@@LIBBPF_0.5.0
     202: 0000000000000000     0 OBJECT  GLOBAL DEFAULT   ABS LIBBPF_0.6.0@@LIBBPF_0.6.0
     ...
The binutils readelf doesn't print out the symbol LIBBPF_* version and llvm-readelf does.
Such a difference caused libbpf build failure with llvm-readelf.

The proposed fix filters out all ABS symbols as they are not part of the comparison.
This works for both binutils readelf and llvm-readelf.

Reported-by: Delyan Kratunov <delyank@...com>
Signed-off-by: Yonghong Song <yhs@...com>
Signed-off-by: Andrii Nakryiko <andrii@...nel.org>
Link: https://lore.kernel.org/bpf/20220204214355.502108-1-yhs@fb.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 tools/lib/bpf/Makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index b393b5e82380..d1b474f3c586 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -129,7 +129,7 @@ GLOBAL_SYM_COUNT = $(shell readelf -s --wide $(BPF_IN_SHARED) | \
 			   sort -u | wc -l)
 VERSIONED_SYM_COUNT = $(shell readelf --dyn-syms --wide $(OUTPUT)libbpf.so | \
 			      sed 's/\[.*\]//' | \
-			      awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}' | \
+			      awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}' | \
 			      grep -Eo '[^ ]+@...BPF_' | cut -d@ -f1 | sort -u | wc -l)
 
 CMD_TARGETS = $(LIB_TARGET) $(PC_FILE)
@@ -192,7 +192,7 @@ check_abi: $(OUTPUT)libbpf.so $(VERSION_SCRIPT)
 		    sort -u > $(OUTPUT)libbpf_global_syms.tmp;		 \
 		readelf --dyn-syms --wide $(OUTPUT)libbpf.so |		 \
 		    sed 's/\[.*\]//' |					 \
-		    awk '/GLOBAL/ && /DEFAULT/ && !/UND/ {print $$NF}'|  \
+		    awk '/GLOBAL/ && /DEFAULT/ && !/UND|ABS/ {print $$NF}'|  \
 		    grep -Eo '[^ ]+@...BPF_' | cut -d@ -f1 |		 \
 		    sort -u > $(OUTPUT)libbpf_versioned_syms.tmp; 	 \
 		diff -u $(OUTPUT)libbpf_global_syms.tmp			 \
-- 
2.34.1