linux-kernel - [PATCH 5.4 18/85] bpf: Prevent .BTF section elimination

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Message-Id: <20201012132633.725047120@linuxfoundation.org>
Date:   Mon, 12 Oct 2020 15:26:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Tony Ambardar <Tony.Ambardar@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH 5.4 18/85] bpf: Prevent .BTF section elimination

From: Tony Ambardar <tony.ambardar@...il.com>

commit 65c204398928f9c79f1a29912b410439f7052635 upstream.

Systems with memory or disk constraints often reduce the kernel footprint
by configuring LD_DEAD_CODE_DATA_ELIMINATION. However, this can result in
removal of any BTF information.

Use the KEEP() macro to preserve the BTF data as done with other important
sections, while still allowing for smaller kernels.

Fixes: 90ceddcb4950 ("bpf: Support llvm-objcopy for vmlinux BTF")
Signed-off-by: Tony Ambardar <Tony.Ambardar@...il.com>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Andrii Nakryiko <andriin@...com>
Link: https://lore.kernel.org/bpf/a635b5d3e2da044e7b51ec1315e8910fbce0083f.1600417359.git.Tony.Ambardar@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/asm-generic/vmlinux.lds.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -599,7 +599,7 @@
 #define BTF								\
 	.BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {				\
 		__start_BTF = .;					\
-		*(.BTF)							\
+		KEEP(*(.BTF))						\
 		__stop_BTF = .;						\
 	}
 #else