linux-kernel - [PATCH] x86/unwind/orc: Fix ORC unwind table alignment

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Message-Id: <d55027ee95fe73e952dcd8be90aebd31b0095c45.1551892041.git.jpoimboe@redhat.com>
Date:   Wed,  6 Mar 2019 11:07:24 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: [PATCH] x86/unwind/orc: Fix ORC unwind table alignment

The .orc_unwind section is a packed array of 6-byte structs.  It's
currently aligned to 6 bytes, which is causing warnings in the LLD
linker.

Six isn't a power of two, so it's not a valid alignment value.  The
actual alignment doesn't matter much because it's an array of packed
structs.  An alignment of two is sufficient.  In reality it always gets
aligned to four bytes because it comes immediately after the
4-byte-aligned .orc_unwind_ip section.

Link: https://github.com/ClangBuiltLinux/linux/issues/218
Fixes: ee9f8fce9964 ("x86/unwind: Add the ORC unwinder")
Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
Reported-by: Dmitry Golovin <dima@...ovin.in>
Reported-by: Sedat Dilek <sedat.dilek@...il.com>
Tested-by: Sedat Dilek <sedat.dilek@...il.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 include/asm-generic/vmlinux.lds.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 3d7a6a9c2370..f8f6f04c4453 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -733,7 +733,7 @@
 		KEEP(*(.orc_unwind_ip))					\
 		__stop_orc_unwind_ip = .;				\
 	}								\
-	. = ALIGN(6);							\
+	. = ALIGN(2);							\
 	.orc_unwind : AT(ADDR(.orc_unwind) - LOAD_OFFSET) {		\
 		__start_orc_unwind = .;					\
 		KEEP(*(.orc_unwind))					\
-- 
2.17.2