From: Pu Lehui <pulehui@huawei.com>
Date: Thu, 21 Oct 2021 20:39:13 +0800
Subject: samples: bpf: Suppress readelf stderr when probing for BTF support
Patch-mainline: v5.16-rc1
Git-commit: 44ce0ac11e4e6dd1aee2e41e7d74f95f3b961cfb
References: jsc#PED-1377

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@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20211021123913.48833-1-pulehui@huawei.com
Acked-by: Shung-Hsi Yu <shung-hsi.yu@suse.com>
---
 samples/bpf/Makefile |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- 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
 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