mirror of https://gitee.com/openkylin/linux.git
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 <dima@golovin.in> Signed-off-by: George Rimar <grimar@accesssoftek.com> Signed-off-by: Tri Vo <trong@android.com> Signed-off-by: Borislav Petkov <bp@suse.de> Tested-by: Tri Vo <trong@android.com> Tested-by: Nick Desaulniers <ndesaulniers@google.com> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Michael Matz <matz@suse.de> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: morbo@google.com Cc: ndesaulniers@google.com Cc: ruiu@google.com Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20190111201012.71210-1-trong@android.com
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@ -100,7 +100,7 @@ $(obj)/zoffset.h: $(obj)/compressed/vmlinux FORCE
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AFLAGS_header.o += -I$(objtree)/$(obj)
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AFLAGS_header.o += -I$(objtree)/$(obj)
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$(obj)/header.o: $(obj)/zoffset.h
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$(obj)/header.o: $(obj)/zoffset.h
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LDFLAGS_setup.elf := -T
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LDFLAGS_setup.elf := -m elf_i386 -T
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$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
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$(obj)/setup.elf: $(src)/setup.ld $(SETUP_OBJS) FORCE
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$(call if_changed,ld)
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$(call if_changed,ld)
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@ -47,7 +47,7 @@ $(obj)/pasyms.h: $(REALMODE_OBJS) FORCE
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targets += realmode.lds
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targets += realmode.lds
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$(obj)/realmode.lds: $(obj)/pasyms.h
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$(obj)/realmode.lds: $(obj)/pasyms.h
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LDFLAGS_realmode.elf := --emit-relocs -T
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LDFLAGS_realmode.elf := -m elf_i386 --emit-relocs -T
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CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj)
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CPPFLAGS_realmode.lds += -P -C -I$(objtree)/$(obj)
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targets += realmode.elf
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targets += realmode.elf
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