From 927185c124d62a9a4d35878d7f6d432a166b74e3 Mon Sep 17 00:00:00 2001 From: George Rimar Date: Fri, 11 Jan 2019 12:10:12 -0800 Subject: [PATCH] x86/build: Specify elf_i386 linker emulation explicitly for i386 objects 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 \ realmode.lds 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: morbo@google.com Cc: ndesaulniers@google.com Cc: ruiu@google.com Cc: x86-ml Link: https://lkml.kernel.org/r/20190111201012.71210-1-trong@android.com --- 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 9b5adae9cc40..e2839b5c246c 100644 --- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE AFLAGS_header.o += -I$(objtree)/$(obj) $(obj)/header.o: $(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 4463fa72db94..96cb20de08af 100644 --- a/arch/x86/realmode/rm/Makefile +++ b/arch/x86/realmode/rm/Makefile @@ -47,7 +47,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE targets += realmode.lds $(obj)/realmode.lds: $(obj)/pasyms.h -LDFLAGS_realmode.elf := --emit-relocs -T +LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj) targets += realmode.elf