linux-kernel - [PATCH x86/tip] x86: ignore R_386_NONE in kernel relocation entries

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Message-ID: <4A1B8150.40702@kernel.org>
Date:	Tue, 26 May 2009 14:42:40 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Linux Kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	the arch/x86 maintainers <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH x86/tip] x86: ignore R_386_NONE in kernel relocation entries

For relocatable 32bit kernels, boot/compressed/relocs.c processes
relocation entries in the kernel image and appends it to the kernel
image such that boot/compressed/head_32.S can relocate the kernel.
The kernel image is one statically linked object and only uses two
relocation types - R_386_PC32 and R_386_32, of the two only the latter
needs massaging during kernel relocation and thus handled by relocs.
R_386_PC32 is ignored and all other relocation types are considered
error.

When the target of a relocation resides in a discarded section,
binutils doesn't throw away the relocation record but nullifies it by
changing it to R_386_NONE, which unfortunately makes relocs fail.

The problem was triggered by yet out-of-tree x86 stack unwind patches
but given the binutils behavior, ignoring R_386_NONE is the right
thing to do.

The problem has been tracke down to binutils behavior by Jan Beulich.

[ Impact: relocs now ignores R_386_NONE ]

Signed-off-by: Tejun Heo <tj@...nel.org>
Cc: Jan Beulich <JBeulich@...ell.com>
Cc: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/boot/compressed/relocs.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/compressed/relocs.c b/arch/x86/boot/compressed/relocs.c
index 857e492..bbeb0c3 100644
--- a/arch/x86/boot/compressed/relocs.c
+++ b/arch/x86/boot/compressed/relocs.c
@@ -504,8 +504,11 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
 			if (sym->st_shndx == SHN_ABS) {
 				continue;
 			}
-			if (r_type == R_386_PC32) {
-				/* PC relative relocations don't need to be adjusted */
+			if (r_type == R_386_NONE || r_type == R_386_PC32) {
+				/*
+				 * NONE can be ignored and and PC relative
+				 * relocations don't need to be adjusted.
+				 */
 			}
 			else if (r_type == R_386_32) {
 				/* Visit relocations that need to be adjusted */
--
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