linux-kernel - [PATCH bpf-next] samples: bpf: Suppress readelf stderr when probing for BTF support

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Date:   Thu, 21 Oct 2021 20:39:13 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     <ast@...nel.org>, <daniel@...earbox.net>, <andrii@...nel.org>,
        <kafai@...com>, <songliubraving@...com>, <yhs@...com>,
        <john.fastabend@...il.com>, <kpsingh@...nel.org>,
        <nathan@...nel.org>, <ndesaulniers@...gle.com>
CC:     <netdev@...r.kernel.org>, <bpf@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>,
        <pulehui@...wei.com>
Subject: [PATCH bpf-next] samples: bpf: Suppress readelf stderr when probing for BTF support

When compiling bpf samples, the following warning appears:

readelf: Error: Missing knowledge of 32-bit reloc types used in DWARF
sections of machine number 247
readelf: Warning: unable to apply unsupported reloc type 10 to section
.debug_info
readelf: Warning: unable to apply unsupported reloc type 1 to section
.debug_info
readelf: Warning: unable to apply unsupported reloc type 10 to section
.debug_info

Same problem was mentioned in commit 2f0921262ba9 ("selftests/bpf:
suppress readelf stderr when probing for BTF support"), let's use
readelf that supports btf.

Signed-off-by: Pu Lehui <pulehui@...wei.com>
---
 samples/bpf/Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index 2366242edb7c..a886dff1ba89 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -229,6 +229,7 @@ CLANG ?= clang
 OPT ?= opt
 LLVM_DIS ?= llvm-dis
 LLVM_OBJCOPY ?= llvm-objcopy
+LLVM_READELF ?= llvm-readelf
 BTF_PAHOLE ?= pahole
 
 # Detect that we're cross compiling and use the cross compiler
@@ -252,7 +253,7 @@ BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
 BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')
 BTF_LLVM_PROBE := $(shell echo "int main() { return 0; }" | \
 			  $(CLANG) -target bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
-			  readelf -S ./llvm_btf_verify.o | grep BTF; \
+			  $(LLVM_READELF) -S ./llvm_btf_verify.o | grep BTF; \
 			  /bin/rm -f ./llvm_btf_verify.o)
 
 BPF_EXTRA_CFLAGS += -fno-stack-protector
-- 
2.17.1