linux-kernel - [PATCH AUTOSEL 5.4 186/459] samples/bpf: Set -fno-stack-protector when building BPF programs

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Date:   Fri, 14 Feb 2020 10:57:16 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <sashal@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, clang-built-linux@...glegroups.com
Subject: [PATCH AUTOSEL 5.4 186/459] samples/bpf: Set -fno-stack-protector when building BPF programs

From: Toke Høiland-Jørgensen <toke@...hat.com>

[ Upstream commit 450278977acbf494a20367c22fbb38729772d1fc ]

It seems Clang can in some cases turn on stack protection by default, which
doesn't work with BPF. This was reported once before[0], but it seems the
flag to explicitly turn off the stack protector wasn't added to the
Makefile, so do that now.

The symptom of this is compile errors like the following:

error: <unknown>:0:0: in function bpf_prog1 i32 (%struct.__sk_buff*): A call to built-in function '__stack_chk_fail' is not supported.

[0] https://www.spinics.net/lists/netdev/msg556400.html

Signed-off-by: Toke Høiland-Jørgensen <toke@...hat.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Link: https://lore.kernel.org/bpf/20191216103819.359535-1-toke@redhat.com
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 samples/bpf/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index e7ad48c605e0f..6d1df7117e117 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -219,6 +219,7 @@ BTF_LLVM_PROBE := $(shell echo "int main() { return 0; }" | \
 			  readelf -S ./llvm_btf_verify.o | grep BTF; \
 			  /bin/rm -f ./llvm_btf_verify.o)
 
+BPF_EXTRA_CFLAGS += -fno-stack-protector
 ifneq ($(BTF_LLVM_PROBE),)
 	EXTRA_CFLAGS += -g
 else
-- 
2.20.1