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Subject[PATCH 4.4 071/168] x86/build: Specify elf_i386 linker emulation explicitly for i386 objects
commit 927185c124d62a9a4d35878d7f6d432a166b74e3 upstream.

The kernel uses the OUTPUT_FORMAT linker script command in it's linker
scripts. Most of the time, the -m option is passed to the linker with
correct architecture, but sometimes (at least for x86_64) the -m option
contradicts the OUTPUT_FORMAT directive.

Specifically, arch/x86/boot and arch/x86/realmode/rm produce i386 object
files, but are linked with the -m elf_x86_64 linker flag when building
for x86_64.

The GNU linker manpage doesn't explicitly state any tie-breakers between
-m and OUTPUT_FORMAT. But with BFD and Gold linkers, OUTPUT_FORMAT
overrides the emulation value specified with the -m option.

LLVM lld has a different behavior, however. When supplied with
contradicting -m and OUTPUT_FORMAT values it fails with the following
error message:

ld.lld: error: arch/x86/realmode/rm/header.o is incompatible with elf_x86_64

Therefore, just add the correct -m after the incorrect one (it overrides
it), so the linker invocation looks like this:

ld -m elf_x86_64 -z max-page-size=0x200000 -m elf_i386 --emit-relocs -T \ header.o trampoline_64.o stack.o reboot.o -o realmode.elf

This is not a functional change for GNU ld, because (although not
explicitly documented) OUTPUT_FORMAT overrides -m EMULATION.

Tested by building x86_64 kernel with GNU gcc/ld toolchain and booting
it in QEMU.

[ bp: massage and clarify text. ]

Suggested-by: Dmitry Golovin <>
Signed-off-by: George Rimar <>
Signed-off-by: Tri Vo <>
Signed-off-by: Borislav Petkov <>
Tested-by: Tri Vo <>
Tested-by: Nick Desaulniers <>
Cc: "H. Peter Anvin" <>
Cc: Ingo Molnar <>
Cc: Michael Matz <>
Cc: Thomas Gleixner <>
Cc: x86-ml <>
[nc: Fix conflicts due to lack of commit 58ab5e0c2c40 ("Kbuild: arch:
look for generated headers in obtree") in this tree]
Signed-off-by: Nathan Chancellor <>
Signed-off-by: Sasha Levin <>
arch/x86/boot/Makefile | 2 +-
arch/x86/realmode/rm/Makefile | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
index 6da2cd0897f3..e94745321cac 100644
--- a/arch/x86/boot/Makefile
+++ b/arch/x86/boot/Makefile
@@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
AFLAGS_header.o += -I$(obj)
$(obj)/header.o: $(obj)/voffset.h $(obj)/zoffset.h

-LDFLAGS_setup.elf := -T
+LDFLAGS_setup.elf := -m elf_i386 -T
$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
$(call if_changed,ld)

diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
index 2730d775ef9a..228cb16962ba 100644
--- a/arch/x86/realmode/rm/Makefile
+++ b/arch/x86/realmode/rm/Makefile
@@ -43,7 +43,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE
targets +=
$(obj)/ $(obj)/pasyms.h

-LDFLAGS_realmode.elf := --emit-relocs -T
+LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T += -P -C -I$(obj)

targets += realmode.elf

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