[tip:x86/urgent] x86, relocs: ignore R_386_NONE in kernel relocation entries

From: tip-bot for Tejun Heo
Date: Tue May 26 2009 - 02:11:34 EST

Commit-ID: 46176b4f6bac19454b7b5c35f68594b85850a600
Gitweb: http://git.kernel.org/tip/46176b4f6bac19454b7b5c35f68594b85850a600
Author: Tejun Heo <tj@xxxxxxxxxx>
AuthorDate: Tue, 26 May 2009 14:42:40 +0900
Committer: H. Peter Anvin <hpa@xxxxxxxxx>
CommitDate: Mon, 25 May 2009 22:52:49 -0700

x86, relocs: 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

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 tracked down to binutils behavior by Jan Beulich.

[ Impact: fix build with certain binutils by ignoring R_386_NONE ]

Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
LKML-Reference: <4A1B8150.40702@xxxxxxxxxx>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>

arch/x86/boot/compressed/relocs.c | 7 +++++--
1 files 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) {
- 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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